When a person is exposed to infestation, the trouble manifests itself

after eight or ten days, though there usually elapses a period of twenty

to thirty days before there is a suspicion of anything serious. The

first symptom is an intense itching which increases when the patient is

in bed. When the point of irritation is examined the galleries may

usually be seen as characteristic sinuous lines, at first whitish in

color but soon becoming blackish because of the contained eggs and

excrement. The galleries, which may not be very distinct in some cases,

may measure as much as four centimeters in length. Little vesicles, of

the size of a pin head are produced by the secretions of the feeding

mite; they are firm, and projecting, and contain a limpid fluid. Figures

58 and 59 show the typical appearance of scabies on the hands, while

figure 60 shows a severe general infestation. The intolerable itching

induces scratching and through this various complications may arise. The

lesions are not normally found on the face and scalp, and are rare on

the back.

[Illustration: 59. Scabies on the hand. After Duhring.]

[Illustration: 60. Generalized infection of Scabies. After Morrow.]

Formerly, scabies was considered a very serious disease, for its cause

and method of treatment were unknown, and potentially it may continue

indefinitely. Generation after generation of the mites may develop and

finally their number become so great that the general health of the

individual is seriously affected. Now that the true cause of the disease

is known, it is easily controlled.

Treatment usually consists in softening the skin by friction with soap

and warm water, followed by a warm bath, and then applying some

substance to kill the mites. Stiles gives the following directions,

modified from Bourguignon's, as "a rather radical guide, to be modified

according to facilities and according to the delicacy of the skin or

condition of the patient":

1. The patient, stripped naked, is energetically rubbed all over (except

the head) for twenty minutes, with green soap and warm water. 2. He is

then placed in a warm bath for thirty minutes, during which time the

rubbing is continued. 3. The parasiticide is next rubbed in for twenty

minutes and is allowed to remain on the body for four or five hours; in

the meantime the patient's clothes are sterilized, to kill the eggs or

mites attached to them. 4. A final bath is taken to remove the

parasiticide.

The parasiticide usually relied on is the officinal sulphur ointment of

the United States pharmacopoeia. When infestation is severe it is

necessary to repeat treatment after three or four days in order to kill

mites which have hatched from the eggs.

The above treatment is too severe for some individuals and may, of

itself, produce a troublesome dermatitis. We have seen cases where the

treatment was persisted in and aggravated the condition because it was

supposed to be due to the parasite. For delicate-skinned patients the

use of balsam of Peru is very satisfactory, and usually causes no

irritation whatever. Of course, sources of reinfection should be

carefully guarded against.

_Sarcoptes scabiei crustosae_, which is a distinct variety, if not

species, of the human itch mite, is the cause of so-called Norwegian

itch. This disease is very contagious, and is much more resistant than

the ordinary scabies. Unlike the latter, it may occur on the face and

scalp.

_Sarcoptes scabiei_ not only attacks man but also occurs on a large

number of mammals. Many species, based on choice of host, and minute

differences in size and secondary characters, have been established, but

most students of the subject relegate these to varietal rank. Many of

them readily attack man, but they have become sufficiently adapted to

their normal host so that they are usually less persistent on man.

_Notoedres cati_ (usually known as _Sarcoptes minor_) is a species of

itch mites which produce an often fatal disease of cats. The body is

rounded and it is considerably smaller than _Sarcoptes scabiei_, the

female (fig. 61) measuring 215-230u long and 165-175u wide; the males

145-150u by 120-125u. The most important character separating

_Notoedres_ from _Sarcoptes_ is the position of the anus, which is

dorsal instead of terminal. The mite readily transfers to man but does

not persist, the infestation usually disappearing spontaneously in about

two weeks. Infested cats are very difficult to cure, unless treatment is

begun at the very inception of the outbreak, and under ordinary

circumstances it is better to kill them promptly, to avoid spread of the

disease to children and others who may be exposed.

[Illustration: 61. Notoedres cati, male and female. After Railliet.]

Demodecidae

The DEMODECIDAE are small, elongate, vermiform mites which live in the

hair follicles of mammals. The family characteristics will be brought

out in the discussion of the species infesting man, _Demodex

folliculorum_.

[Illustration: 62. Demodex folliculorum. (x200) After Blanchard.]

_Demodex folliculorum_ (fig. 62) is to be found very commonly in the

hair follicles and sebaceous glands of man. It is vermiform in

appearance, and with the elongate abdomen transversely striated so as to

give it the appearance of segmentation. The female is 380-400u long by

45u; the male 300u by 40u. The three-jointed legs, eight in number, are

reduced to mere stubs in the adult. The larval form is hexopod. These

mites thus show in their form a striking adaptation to their

environment. In the sebaceous glands and hair follicles they lie with

their heads down (fig. 63). Usually there are only a few in a gland, but

Gruby has counted as many as two hundred.

[Illustration: 63. Demodex folliculorum. Section through skin showing

the mites in situ. Magnification of Nos. 1, 2, 6 and 7, x150; Nos, 3,

4, 5, x450. After Megnin.]

The frequency with which they occur in man is surprising. According to

European statistics they are found in 50 per cent to 60 per cent or even

more. Gruby found them in forty out of sixty persons examined. These

figures are very commonly quoted, but reliable data for the United

States seem to be lacking. Our studies indicate that it is very much

less common in this country than is generally assumed.

The Demodex in man does not, as a rule, cause the slightest

inconvenience to its host. It is often stated that they give rise to

comedons or "black-heads" but there is no clear evidence that they are

ever implicated. Certain it is that they are not the usual cause. A

variety of the same, or a very closely related species of _Demodex_, on

the dog gives rise to the very resistant and often fatal follicular

mange.

HEXAPODA OR TRUE INSECTS

The HEXAPODA, or true insects, are characterized by the fact that the

adult possesses three pairs of legs. The body is distinctly segmented

and is divided into head, thorax, and abdomen.

The mouth-parts in a generalized form, consist of an upper lip, or

_labrum_, which is a part of the head capsule, and a central unpaired

_hypopharynx_, two _mandibles_, two _maxillae_ and a lower lip, or

_labium_, made up of the fused pair of second maxillae. These parts may

be greatly modified, dependent upon whether they are used for biting,

sucking, piercing and sucking, or a combination of biting and sucking.

Roughly speaking, insects may be grouped into those which undergo

_complete metamorphosis_ and those which have _incomplete

metamorphosis_. They are said to undergo complete metamorphosis when the

young form, as it leaves the egg, bears no resemblance to the adult. For

example, the maggot changes to a quiescent pupa and from this emerges

the winged active fly. They undergo incomplete metamorphosis, when the

young insect, as it leaves the egg, resembles the adult to a greater or

less extent, and after undergoing a certain number of molts becomes

sexually mature.

Representatives of several orders have been reported as accidental or

faculative parasites of man, but the true parasites are restricted to

four orders. These are the Siphunculata; the Hemiptera, the Diptera and

the Siphonaptera.

SIPHUNCULATA

The order SIPHUNCULATA was established by Meinert to include the true

sucking lice. These are small wingless insects, with reduced

mouth-parts, adapted for sucking; thorax apparently a single piece due

to indistinct separation of its three segments: the compound eyes

reduced to a single ommatidium on each side. The short, powerful legs

are terminated by a single long claw. Metamorphosis incomplete.

There has been a great deal of discussion regarding the structure of the

mouth-parts, and the relationships of the sucking lice, and the

questions cannot yet be regarded as settled. The conflicting views are

well represented by Cholodkovsky (1904 and 1905) and by Enderlein

(1904).

[Illustration: 64. Pediculus showing the blind sac (_b_) containing the

mouth parts (_a_) beneath the alimentary canal (_p_). After Pawlowsky.]

Following Graber, it is generally stated that the mouth-parts consist of

a short tube furnished with hooks in front, which constitutes the lower

lip, and that within this is a delicate sucking tube derived from the

fusion of the labrum and the mandibles. Opposed to this, Cholodkovsky

and, more recently, Pawlowsky, (1906), have shown that the piercing

apparatus lies in a blind sac under the pharynx and opening into the

mouth cavity (fig. 64). It does not form a true tube but a furrow with

its open surface uppermost. Eysell has shown that, in addition, there is

a pair of chitinous rods which he regards as the homologues of the

maxillae.

When the louse feeds, it everts the anterior part of the mouth cavity,

with its circle of hooks. The latter serve for anchoring the bug, and

the piercing apparatus is then pushed out.

[Illustration: 65. Pediculus humanus, ventral aspect of male. (x10)]

Most writers have classed the sucking lice as a sub-order of the

Hemiptera, but the more recent anatomical and developmental studies

render this grouping untenable. An important fact, bearing on the

question, is that, as shown by Gross, (1905), the structure of the

ovaries is radically different from that of the Hemiptera.

Lice infestation and its effects are known medically as _pediculosis_.

Though their continued presence is the result of the grossest neglect

and filthiness, the original infestation may be innocently obtained and

by people of the most careful habits.

Three species commonly attack man. Strangely enough, there are very few

accurate data regarding their life history.

_Pediculus humanus_ (fig. 65), the head louse, is the most widely

distributed. It is usually referred to in medical literature as

_Pediculus capitis_, but the Linnean specific name has priority. In

color it is of a pale gray, blackish on the margins. It is claimed by

some authors that the color varies according to the color of the skin of

the host. The abdomen is composed of seven distinct segments, bearing

spiracles laterally. There is considerable variation in size. The males

average 1.8 mm. and the females 2.7 mm. in length.

The eggs, fifty to sixty in number, stick firmly to the hairs of the

host and are known as nits. They are large and conspicuous, especially

on dark hair and are provided with an operculum, or cap, at the free

end, where the nymphs emerge. They hatch in about six days and about the

eighteenth day the young lice are sexually mature.

[Illustration: 66. Pediculosis of the head. The illustration shows the

characteristic indications of the presence of lice, viz: the occipital

eczema gluing the hairs together, the swollen cervical glands, and the

porrigo, or eruption of contagious pustules upon the neck. After Fox.]

The head lice live by preference on the scalp of their host but

occasionally they are found on the eyelashes and beard, or in the pubic

region. They may also occur elsewhere on the body. The penetration of

the rostrum into the skin and the discharge of an irritating saliva

produce a severe itching, accompanied by the formation of an eczema-like

eruption (fig. 66). When the infestation is severe, the discharge from

the pustules mats down the hair, and scabs are formed, under which the

insects swarm. "If allowed to run, a regular carapace may form, called

_trichoma_, and the head exudes a foetid odor. Various low plants may

grow in the trichoma, the whole being known as _plica

palonica_."--Stiles.

Sources of infestation are various. School children may obtain the lice

from seatmates, by wearing the hats or caps of infested mates, or by the

use, in common, of brushes and combs. They may be obtained from infested

beds or sleeper berths. Stiles reports an instance in which a large

number of girls in a fashionable boarding school developed lousiness a

short time after traveling in a sleeping car.

Treatment is simple, for the parasites may readily be controlled by

cleanliness and washing the head with a two per cent solution of

carbolic acid or even kerosene. The latter is better used mixed with

equal parts of olive oil, to avoid irritation. The treatment should be

applied at night and followed the next morning by a shampoo with soap

and warm water. It is necessary to repeat the operation in a few days.

Xylol, used pure, or with the addition of five per cent of vaseline, is

also very efficacious. Of course, the patient must be cautioned to stay

away from a lighted lamp or fire while using either the kerosene or

xylol. While these treatments will kill the eggs or nits, they will not

remove them from the hairs. Pusey recommends repeated washings with

vinegar or 25 per cent of acetic acid in water, for the purpose of

loosening and removing the nits.

Treatment of severe infestations in females is often troublesome on

account of long hair. For such cases the following method recommended by

Whitfield (1912) is especially applicable:

The patient is laid on her back on the bed with her head over the edge,

and beneath the head is placed a basin on a chair so that the hair lies

in the basin. A solution of 1 in 40 carbolic acid is then poured over

the hair into the basin and sluiced backwards and forwards until the

whole of the hair is thoroughly soaked with it. It is especially

necessary that care should be taken to secure thorough saturation of the

hair over the ears and at the nape of the neck, since these parts are

not only the sites of predilection of the parasites but they are apt to

escape the solution. This sluicing is carried out for ten minutes by the

clock. At the end of ten minutes the hair is lifted from the basin and

allowed to drain, but is not dried or even thoroughly wrung out. The

whole head is then swathed with a thick towel or better, a large piece

of common house flannel, which is fastened up to form a sort of turban,

and is allowed to remain thus for an hour. It can then be washed or

simply allowed to dry, as the carbolic quickly disperses. At the end of

this period every pediculus and what is better, every ovum is dead and

no relapse will occur unless there is exposure to fresh contagion.

Whitfield states that there seem to be no disadvantages in this method,

which he has used for years. He has never seen carboluria result from

it, but would advise first cutting the hair of children under five years

of age.

_Pediculus corporis_ (= _P. vestimenti_) the body louse, is larger than

the preceding species, the female measuring 3.3 mm., and the male 3 mm.

in length. The color is a dirty white, or grayish. _P. corporis_ has

been regarded by some authorities as merely a variety of _P. humanus_

but Piaget maintains there are good characters separating the two

species.

The body louse lives in the folds and seams of the clothing of its host,

passing to the skin only when it wishes to feed. Brumpt states that he

has found enormous numbers of them in the collars of glass-ware or

grains worn by certain naked tribes in Africa.

Exact data regarding the life-history of this species have been

supplied, in part, by the work of Warburton (1910), cited by Nuttall. He

found that _Pediculus corporis_ lives longer than _P. humanus_ under

adverse conditions. This is doubtless due to its living habitually on

the clothing, whereas _humanus_ lives upon the head, where it has more

frequent opportunities of feeding. He reared a single female upon his

own person, keeping the louse enclosed in a cotton-plugged tube with a

particle of cloth to which it could cling. The tube was kept next to his

body, thus simulating the natural conditions of warmth and moisture

under which the lice thrive. The specimen was fed twice daily, while it

clung to the cloth upon which it rested. Under these conditions she

lived for one month. Copulation commenced five days after the female had

hatched and was repeated a number of times, sexual union lasting for

hours. The female laid one hundred and twenty-four eggs within

twenty-five days.

The eggs hatched after eight days, under favorable conditions, such as

those under which the female was kept. They did not hatch in the cold.

Eggs kept near the person during the day and hung in clothing by the

bedside at night, during the winter, in a cold room, did not hatch until

the thirty-fifth day. When the nymphs emerge from the eggs, they feed at

once, if given a chance to do so. They are prone to scatter about the

person and abandon the fragment of cloth to which the adult clings.

The adult stage is reached on the eleventh day, after three molts, about

four days apart. Adults enter into copulation about the fifth day and as

the eggs require eight days for development, the total cycle, under

favorable conditions, is about twenty-four days. Warburton's data differ

considerably from those commonly quoted and serve to emphasize the

necessity for detailed studies of some of the commonest of parasitic

insects.

Body lice are voracious feeders, producing by their bites and the

irritating saliva which they inject, rosy elevations and papules which

become covered with a brownish crust. The intense itching provokes

scratching, and characteristic white scars (fig. 67) surrounded by

brownish pigment (fig. 68) are formed. The skin may become thickened and

take on a bronze tinge. This melanoderma is especially marked in the

region between the shoulders but it may become generalized, a prominent

characteristic of "vagabond's disease." According to Dubre and Beille,

this melanoderma is due to a toxic substance secreted by the lice, which

indirectly provokes the formation of pigment.

[Illustration: 67. Pediculosis in man caused by the body louse. After

Morrow.]

Control measures, in the case of the body louse, consist in boiling or

steaming the clothes or in some cases, sterilizing by dry heat. The

dermatitis may be relieved by the use of zinc-oxide ointment, to which

Pusey recommends that there be added, on account of their parasiticidal

properties, sulphur and balsam of Peru, equal parts, 15 to 30 grains to

the ounce.

_Phthirius pubis_ (= _P. inguinalis_), the pubic louse, or so-called

"crab louse," differs greatly from the preceding in appearance. It is

characterized by its relatively short head which fits into a broad

depression in the thorax. The latter is broad and flat and merges into

the abdomen. The first pair of legs is slender and terminated by a

straight claw. The second and third pairs of legs are thicker and are

provided with powerful claws fitted for clinging to hairs. The females

(fig. 69) measure 1.5 to 2 mm. in length by 1.5 mm. in breadth. The male

averages a little over half as large. The eggs, or nits, are fixed at

the base of the hairs. Only a few, ten to fifteen are deposited by a

single female, and they hatch in about a week's time. The young lice

mature in two weeks.

The pubic louse usually infests the hairs of the pubis and the perineal

region. It may pass to the arm pits or even to the beard or moustache.

Rarely, it occurs on the eyelids, and it has even been found, in a very

few instances, occurring in all stages, on the scalp. Infestation may be

contracted from beds or even from badly infested persons in a crowd. We

have seen several cases which undoubtedly were due to the use of public

water closets. It produces papular eruption and an intense pruritis.

When abundant, there occurs a grayish discoloration of the skin which

Duguet has shown is due to a poisonous saliva injected by the louse, as

is the melanoderma caused by the body louse.

[Illustration: 68. Melanoderma caused by the body louse. From Portfolio

of Dermochromes, by permission of Rebman & Co., New York, Publishers.]

The pubic louse may be exterminated by the measures recommended for the

head louse, or by the use of officinal mercurial ointment.

[Illustration: 69. Phthirius pubis. Ventral aspect of female. (x12).]

HEMIPTERA

Several species of HEMIPTERA-HETEROPTERA are habitual parasites of man,

and others occur as occasional or accidental parasites. Of all these,

the most important and widespread are the bed-bugs, belonging to the

genus _Cimex_ (= _Acanthia_).

THE BED-BUGS--The bed-bugs are characterized by a much flattened oval

body, with the short, broad head unconstricted behind, and fitting into

the strongly excavated anterior margin of the thorax. The compound eyes

are prominent, simple eyes lacking. Antennae four-jointed, the first

segment short, the second long and thick, and the third and fourth

slender. The tarsi are short and three segmented.

It is often assumed in the literature of the subject that there is but a

single species of _Cimex_ attacking man, but several such species are to

be recognized. These are distinguishable by the characters given in

Chapter XII. We shall consider especially _Cimex lectularius_, the most

common and widespread species.

_Cimex lectularius_ (= _Acanthia lectularia_, _Clinocoris

lectularius_), is one of the most cosmopolitan of human parasites but,

like the lice, it has been comparatively little studied until recent

years, when the possibility that it may be concerned with the

transmission of various diseases has awakened interest in the details of

its life-history and habits.

[Illustration: 70. Cimex lectularius adult and eggs. Photograph by M. V.

S.]

The adult insect (fig. 70) is 4-5 mm. long by 3 mm. broad, reddish brown

in color, with the beak and body appendages lighter in color. The short,

broad and somewhat rectangular head has no neck-like constriction but

fits into the broadly semilunar prothorax. The four segmented labium or

proboscis encloses the lancet-like maxillae and mandibles. The distal

of the four antennal segments is slightly club-shaped. The prothorax is

characteristic of the species, being deeply incised anteriorly and with

its thin lateral margins somewhat turned up. The mesothorax is

triangular, with the apex posteriorly, and bears the greatly atrophied

first pair of wings. There is no trace of the metathoracic pair. The

greatly flattened abdomen has eight visible segments, though in reality

the first is greatly reduced and has been disregarded by most writers.

The body is densely covered with short bristles and hairs, the former

being peculiarly saber-shaped structures sharply toothed at the apex and

along the convex side (fig. 159_b_).

The peculiar disagreeable odor of the adult bed-bug is due to the

secretion of the stink glands which lie on the inner surface of the

mesosternum and open by a pair of orifices in front of the metacoxae,

near the middle line. In the nymphs, the thoracic glands are not

developed but in the abdomen there are to be found three unpaired dorsal

stink glands, which persist until the fifth molt, when they become

atrophied and replaced by the thoracic glands. The nymphal glands occupy

the median dorsal portion of the abdomen, opening by paired pores at the

anterior margin of the fourth, fifth and sixth segments. The secretion

is a clear, oily, volatile fluid, strongly acid in reaction. Similar

glands are to be found in most of the Hemiptera-Heteroptera and their

secretion is doubtless protective, through being disagreeable to the

birds. In the bed-bug, as Marlatt points out, "it is probably an

illustration of a very common phenomenon among animals, i.e., the

persistence of a characteristic which is no longer of any special value

to the possessor." In fact, its possession is a distinct disadvantage to

the bed-bug, as the odor frequently reveals the presence of the bugs,

before they are seen.

The eggs of the bed-bug (fig. 70) are pearly white, oval in outline,

about a millimeter long, and possess a small operculum or cap at one

end, which is pushed off when the young hatches. They are laid

intermittently, for a long period, in cracks and crevices of beds and

furniture, under seams of mattresses, under loose wall paper, and

similar places of concealment of the adult bugs. Girault (1905) observed

a well-fed female deposit one hundred and eleven eggs during the

sixty-one days that she was kept in captivity. She had apparently

deposited some of her eggs before being captured.

The eggs hatch in six to ten days, the newly emerged nymphs being about

1.5 mm. in length and of a pale yellowish white color. They grow slowly,

molting five times. At the last molt the mesathoracic wing pads appear,

characteristic of the adult. The total length of the nymphal stage

varies greatly, depending upon conditions of food supply, temperature

and possibly other factors. Marlatt (1907) found under most favorable

conditions a period averaging eight days between molting which, added to

an equal egg period, gave a total of about seven weeks from egg to adult

insect. Girault (1912) found the postembryonic period as low as

twenty-nine days and as high as seventy days under apparently similar

and normal conditions of food supply. Under optimum and normal

conditions of food supply, beginning August 27, the average nymphal life

was 69.9 days; average number of meals 8.75 and the molts 5. Under

conditions allowing about half the normal food supply the average

nymphal life was from 116.9 to 139 days. Nymphs starved from birth lived

up to 42 days. We have kept unfed nymphs, of the first stage, alive in a

bottle for 75 days. The interesting fact was brought out that under

these conditions of minimum food supply there were sometimes six molts

instead of the normal number.

The adults are remarkable for their longevity, a factor which is of

importance in considering the spread of the insect and methods of

control. Dufour (1833) (not De Geer, as often stated) kept specimens for

a year, in a closed vial, without food. This ability, coupled with their

willingness to feed upon mice, bats, and other small mammals, and even

upon birds, accounts for the long periods that deserted houses and camps

may remain infested. There is no evidence that under such conditions

they are able to subsist on the starch of the wall paper, juices of

moistened wood, or the moisture in the accumulations of dust, as is

often stated.

There are three or four generations a year, as Girault's breeding

experiments have conclusively shown. He found that the bed-bug does not

hibernate where the conditions are such as to allow it to breed and that

breeding is continuous unless interrupted by the lack of food or, during

the winter, by low temperature.

Bed-bugs ordinarily crawl from their hiding places and attack the face

and neck or uncovered parts of the legs and arms of their victims. If

undisturbed, they will feed to repletion. We have found that the young

nymph would glut itself in about six minutes, though some individuals

fed continuously for nine minutes, while the adult required ten to

fifteen minutes for a full meal. When gorged, it quickly retreats to a

crack or crevice to digest its meal, a process which requires two or

three days. The effect of the bite depends very greatly on the

susceptibility of the individual attacked. Some persons are so little

affected that they may be wholly ignorant of the presence of a large

number of bugs. Usually the bite produces a small hard swelling, or

wheal, whitish in color. It may even be accompanied by an edema and a

disagreeable inflammation, and in such susceptible individuals the

restlessness and loss of sleep due to the presence of the insects may be

a matter of considerable importance. Stiles (1907) records the case of a

young man who underwent treatment for neurasthenia, the diagnosis being

agreed upon by several prominent physicians; all symptoms promptly

disappeared, however, immediately following a thorough fumigation of

his rooms, where nearly a pint of bed-bugs were collected.

It is natural to suppose that an insect which throughout its whole life

is in such intimate relationship with man should play an important role

in the transmission of disease. Yet comparatively little is definitely

known regarding the importance of the bed-bug in this respect. It has

been shown that it is capable of transmitting the bubonic plague, and

South American trypanosomiasis. Nuttall succeeded in transmitting

European relapsing fever from mouse to mouse by its bite. It has been

claimed that Oriental sore, tuberculosis, and even syphilis may be so

carried. These phases of the subject will be considered later.

The sources of infestation are many, and the invasion of a house is not

necessarily due to neglect, though the continued presence of the pests

is quite another matter. In apartments and closely placed houses they

are known to invade new quarters by migration. They are frequently to be

met with in boat and sleeper berths, and even the plush seats of day

coaches, whence a nucleus may be carried in baggage to residences. They

may be brought in the laundry or in clothes of servants.

Usually they are a great scourge in frontier settlements and it is

generally believed that they live in nature under the bark of trees, in

lumber, and under similar conditions. This belief is founded upon the

common occurrence of bugs resembling the bed-bug, in such places. As a

matter of fact, they are no relation to bed-bugs but belong to

plant-feeding forms alone (fig. 19 _c_, _d_).

It is also often stated that bed-bugs live in poultry houses, in

swallows nests, and on bats, and that it is from these sources that they

gain access to dwellings. These bugs are specifically distinct from the

true bed-bug, but any of them may, rarely, invade houses. Moreover,

chicken houses are sometimes thoroughly infested with the true _Cimex

lectularius_.

Control measures consist in the use of iron bedsteads and the reduction

of hiding places for the bugs. If the infestation is slight they may be

exterminated by a vigilant and systematic hunt, and by squirting

gasoline or alcohol into cracks and crevices of the beds, and furniture.

Fumigation must be resorted to in more general infestations.

The simplest and safest method of fumigation is by the use of flowers of

sulphur at the rate of two pounds to each one thousand cubic feet of

room space. The sulphur should be placed in a pan, a well made in the

top of the pile and a little alcohol poured in, to facilitate burning.

The whole should be placed in a larger pan and surrounded by water so as

to avoid all danger of fire. Windows should be tightly closed, beds,

closets and drawers opened, and bedding spread out over chairs in order

to expose them fully to the fumes. As metal is tarnished by the sulphur

fumes, ornaments, clocks, instruments, and the like should be removed.

When all is ready the sulphur should be fired, the room tightly closed

and left for twelve to twenty-four hours. Still more efficient in large

houses, or where many hiding places favor the bugs, is fumigation with

hydrocyanic acid gas. This is a deadly poison and must be used under

rigid precautions. Through the courtesy of Professor Herrick, who has

had much experience with this method, we give in the Appendix, the clear

and detailed directions taken from his bulletin on "Household Insects."

Fumigation with formaldehyde gas, either from the liquid or "solid"

formalin, so efficient in the case of contagious diseases, is useless

against bed-bugs and most other insects.

OTHER BED-BUGS--_Cimex hemipterus_ (= _C. rotundatus_) is a tropical and

subtropical species, occurring in both the old and new world. Patton and

Cragg state that it is distributed throughout India, Burma, Assam, the

Malay Peninsula, Aden, the Island of Mauritius, Reunion, St. Vincent and

Porto Rico. "It is widely distributed in Africa, and is probably the

common species associated there with man." Brumpt also records it for

Cuba, the Antilles, Brazil, and Venezuela.

This species, which is sometimes called the Indian bed-bug, differs from

_C. lectularius_ in being darker and in having a more elongate abdomen.

The head also is shorter and narrower, and the prothorax has rounded

borders.

It has the same habits and practically the same life cycle as _Cimex

lectularius_. Mackie, in India, has found that it is capable of

transmitting the Asiatic type of recurrent fever. Roger suggested that

it was also capable of transmitting Kala-azar and Patton has described

in detail the developmental stages of _Leishmania_, the causative

organism of Kala-azar, in the stomach of this bug, but Brumpt declares

that the forms described are those of a common, non-pathogenic

flagellate to be found in the bug, and have nothing to do with the

human disease. Brumpt has shown experimentally that _Cimex hemipterus_

may transmit _Trypanosoma cruzi_ in its excrement.

_Cimex boueti_, occurring in French Guinea, is another species attacking

man. Its habits and general life history are the same as for the above

species. It is 3 to 4.5 mm. in length, has vestigial elytra, and much

elongated antennae and legs. The extended hind legs are about as long as

the body.

_Cimex columbarius_, a widely distributed species normally living in

poultry houses and dove cotes, _C. inodorus_, infesting poultry in

Mexico, _C. hirundinis_, occurring in the nests of swallows in Europe

and _Oeciacus vicarius_ (fig. 19i) occurring in swallows' nests in this

country, are species which occasionally infest houses and attack man.

[Illustration: 71. Conorhinus sanguisugus.]

_Conorhinus sanguisugus_, the cone-nosed bed-bug. We have seen in our

consideration of poisonous insects, that various species of Reduviid

bugs readily attack man. Certain of these are nocturnal and are so

commonly found in houses that they have gained the name, of "big

bed-bugs." The most noted of these, in the United States, is _Conorhinus

sanguisugus_ (fig. 71), which is widely distributed in our Southern

States.

Like its near relatives, _Conorhinus sanguisugus_ is carnivorous in

habit and feeds upon insects as well as upon mammalian and human blood.

It is reported as often occurring in poultry houses and as attacking

horses in barns. The life history has been worked out in considerable

detail by Marlatt, (1902), from whose account we extract the following.

[Illustration: 72. Beak of Conorhinus sanguisugus. After Marlatt.]

The eggs are white, changing to yellow and pink before hatching. The

young hatch within twenty days and there are four nymphal stages. In all

these stages the insect is active and predaceous, the mouth-parts (fig.

72) being powerfully developed. The eggs are normally deposited, and the

early stages are undoubtedly passed, out of doors, the food of the

immature forms being other insects. Immature specimens are rarely found

indoors. It winters both in the partly grown and adult stage, often

under the bark of trees or in any similar protection, and only in its

nocturnal spring and early summer flights does it attack men. Marlatt

states that this insect seems to be decidedly on the increase in the

region which it particularly infests,--the plains region from Texas

northward and westward. In California a closely related species of

similar habits is known locally as the "monitor bug."

The effect of the bite of the giant bed-bug on man is often very severe,

a poisonous saliva apparently being injected into the wound. We have

discussed this phase of the subject more fully under the head of

poisonous insects.

_Conorhinus megistus_ is a Brazilian species very commonly attacking

man, and of special interest since Chagas has shown that it is the

carrier of a trypanosomiasis of man. Its habits and life history have

been studied in detail by Neiva, (1910).

This species is now pre-eminently a household insect, depositing its

eggs in cracks and crevices in houses, though this is a relatively

recent adaptation. The nymphs emerge in from twenty to forty days,

depending upon the temperature. There are five nymphal stages, and as in

the case of true bed-bugs, the duration of these is very greatly

influenced by the availability of food and by temperature. Neiva reckons

the entire life cycle, from egg to egg, as requiring a minimum of three

hundred and twenty-four days.

The nymphs begin to suck blood in three to five days after hatching.

They usually feed at night and in the dark, attacking especially the

face of sleeping individuals. The bite occasions but little pain. The

immature insects live in cracks and crevices in houses and invade the

beds which are in contact with walls, but the adults are active flyers

and attack people sleeping in hammocks. The males as well as the females

are blood suckers.

Like many blood-sucking forms, _Conorhinus megistus_ can endure for long

periods without food. Neiva received a female specimen which had been

for fifty-seven days alive in a tightly closed box. They rarely feed on

two consecutive days, even on small quantities of blood, and were never

seen to feed on three consecutive days.

Methods of control consist in screening against the adult bugs, and the

elimination of crevices and such hiding places of the nymphs. Where the

infestation is considerable, fumigation with sulphur is advisable.

PARASITIC DIPTERA OR FLIES

Of the DIPTERA or two-winged flies, many species occasionally attack

man. Of these, a few are outstanding pests, many of them may also serve

to disseminate disease, a phase of our subject which will be considered

later. We shall now consider the most important of the group from the

viewpoint of their direct attacks on man.

Psychodidae or Moth-Flies

The PSYCHODIDAE or Moth-flies, include a few species which attack man,

and at least one species, _Phlebotomus papatasii_, is known to transmit

the so-called "three-day fever" of man. Another species is supposed to

be the vector of Peruvian verruga.

The family is made up of small, sometimes very small, nematocerous

Diptera, which are densely covered with hairs, giving them a moth-like

appearance. The wings are relatively large, oval or lanceolate in shape,

and when at rest are held in a sloping manner over the abdomen, or are

held horizontally in such a way as to give the insect a triangular

outline. Not only is the moth-like appearance characteristic, but the

venation of the wings (fig. 163, d) is very peculiar and, according to

Comstock, presents an extremely generalized form. All of the

longitudinal veins separate near the base of the wing except veins R_2

and R_3 and veins M_1 and M_2. Cross veins are wanting in most cases.

Comparatively little is known regarding the life-history and habits of

the Psychodidae, but one genus, _Phlebotomus_, contains minute,

blood-sucking species, commonly known as sand-flies. The family is

divided into two subfamilies, the PSYCHODINAE and the PHLEBOTOMINAE.

The second of these, the PHLEBOTOMINAE, is of interest to us.

THE PHLEBOTOMINAE--The Phlebotominae differ from the Psychodinae

in that the radical sector branches well out into the wing rather than

at the base of the wing. They are usually less hairy than the

Psychodinae. The ovipositor is hidden and less strongly chitinized.

The species attacking man belong to the genus _Phlebotomus_, small forms

with relatively large, hairy wings which are held upright, and with

elongate proboscis. The mandibles and maxillae are serrated and fitted

for biting.

According to Miss Summers (1913) there are twenty-nine known species of

the genus _Phlebotomus_, five European, eleven Asiatic, seven African

and six American. One species only, _Phlebotomus vexator_, has been

reported for the United States. This was described by Coquillett,

(1907), from species taken on Plummer's Island, Maryland. It measures

only 1.5 mm. in length. As it is very probable that this species is much

more widely distributed, and that other species of these minute flies

will be found to occur in our fauna, we quote Coquillett's description.

_Phlebotomus vexator_, Coq.: Yellow, the mesonotum brown, hairs chiefly

brown; legs in certain lights appear brown, but are covered with a white

tomentum; wings hyaline, unmarked; the first vein (R_1) terminates

opposite one-fifth of the length of the first submarginal cell (cell

R_2); this cell is slightly over twice as long as its petiole; terminal,

horny portion of male claspers slender, bearing many long hairs; the

apex terminated by two curved spines which are more than one-half as

long as the preceding part, and just in front of these are two similar

spines, while near the middle of the length of this portion is a fifth

spine similar to the others. Length 1.5 mm.

The life-history of the Phlebotomus flies has been best worked out for

the European _Phlebotomus papatasii_ and we shall briefly summarize the

account of Doerr and Russ (1913) based primarily on work on this

species. The European Phlebotomus flies appear at the beginning of the

warm season, a few weeks after the cessation of the heavy rains and

storms of springtime. They gradually become more abundant until they

reach their first maximum, which in Italy is near the end of July

(Grassi). They then become scarcer but reach a second maximum in

September. At the beginning of winter they vanish completely,

hibernating individuals not being found.

After fertilization there is a period of eight to ten days before

oviposition. The eggs are then deposited, the majority in a single mass

covered by a slimy secretion from the sebaceous glands. The larvae emerge

in fourteen to twenty days. There is uncertainty as to the length of

larval life, specimens kept in captivity remaining fifty or more days

without transforming. Growth may be much more rapid in nature. The larvae

do not live in fluid media but in moist detritus in dark places. Marett

believes that they live chiefly on the excrement of pill-bugs (Oniscidae)

and lizards. Pupation always occurs during the night. The remnants of

the larval skin remain attached to the last two segments of the

quiescent pupa and serve to attach it to the stone on which it lives.

The pupal stage lasts eleven to sixteen days, the adult escaping at

night.

Only the females suck blood. They attack not only man but all

warm-blooded animals and, according to recent workers, also cold-blooded

forms, such as frogs, lizards, and larvae. Indeed, Townsend (1914)

believes that there is an intimate relation between _Phlebotomus_ and

lizards, or other reptiles the world over. The Phlebotomus passes the

daylight hours within the darkened recesses of the loose stone walls and

piles of rock in order to escape wind and strong light. Lizards inhabit

the same places, and the flies, always ready to suck blood in the

absence of light and wind, have been found more prone to suck reptilian

than mammalian blood.

On hot summer nights, when the wind is not stirring, the Phlebotomus

flies, or sand-flies, as they are popularly called, invade houses and

sleeping rooms in swarms and attack the inmates. As soon as light begins

to break the flies either escape to the breeding places, or cool, dark

places protected from the wind, or a part of them remain in the rooms,

hiding behind pictures, under garments, and in similar places. Wherever

the Phlebotomus flies occur they are an intolerable nuisance. On account

of their small size they can easily pass through the meshes of ordinary

screens and mosquito curtains. They attack silently and inflict a very

painful, stinging bite, followed by itching. The ankles, dorsum of the

feet, wrists, inner elbow, knee joint and similar places are favorite

places of attack, possibly on account of their more delicate skin.

Special interest has been attracted to these little pests in recent

years, since it has been shown that they transmit the European

"pappatici fever" or "three day fever." More recently yet, it appears

that they are the carriers of the virus of the Peruvian "verruga." This

phase of the subject will be discussed later.

Control measures have not been worked out. As Newstead says, "In

consideration of the facts which have so far been brought to light

regarding the economy of Phlebotomus, it is clearly evident that the

task of suppressing these insects is an almost insurmountable one. Had

we to deal with insects as large and as accessible as mosquitoes, the

adoption of prophylactic measures would be comparatively easy, but owing

to the extremely minute size and almost flea-like habits of the adult

insects, and the enormous area over which the breeding-places may occur,

we are faced with a problem which is most difficult of solution." For

these reasons, Newstead considers that the only really prophylactic

measures which can at present be taken, are those which are considered

as precautionary against the bites of the insects.

Of repellents, he cites as one of the best a salve composed of the

following:

Ol. Anisi 3 grs.

Ol. Eucalypti 3 grs.

Ol. Terebenth 3 grs.

Unq. Acid Borac.

Of sprays he recommends as the least objectionable and at the same time

one of the most effective, formalin. "The dark portions and angles of

sleeping apartments should be sprayed with a one per cent. solution of

this substance every day during the season in which the flies are

prevalent. A fine spraying apparatus is necessary for its application

and an excessive amount must not be applied. It is considered an

excellent plan also to spray the mosquito curtains regularly every day

towards sunset; nets thus treated are claimed to repel the attacks of

these insects." This effectiveness of formalin is very surprising for,

as we have seen, it is almost wholly ineffective against bed-bugs,

mosquitoes, house flies and other insects, where it has been tried.

A measure which promises to be very effective, where it can be adopted,

is the use of electric fans so placed as to produce a current of air in

the direction of the windows of sleeping apartments. On account of the

inability of the Phlebotomus flies to withstand even slight breezes, it

seems very probable that they would be unable to enter a room so

protected.

Culicidae or Mosquitoes

From the medical viewpoint, probably the most interesting and important

of the blood-sucking insects are the mosquitoes. Certainly this is true

of temperate zones, such as those of the United States. The result is

that no other group of insects has aroused such widespread interest, or

has been subjected to more detailed study than have the mosquitoes,

since their role as carriers of disease was made known. There is an

enormous literature dealing with the group, but fortunately for the

general student, this has been well summarized by a number of workers.

The most important and helpful of the general works are those of Howard

(1901), Smith (1904), Blanchard (1905), Mitchell (1907), and especially

of Howard, Dyar, and Knab, whose magnificent monograph is still in

course of publication.

Aside from their importance as carriers of disease, mosquitoes are

notorious as pests of man, and the earlier literature on the group is

largely devoted to references to their enormous numbers and their

blood-thirstiness in certain regions. They are to be found in all parts

of the world, from the equator to the Arctic and Antarctic regions.

Linnaeus, in the "Flora Lapponica," according to Howard, Dyar and Knab,

"dwells at some length upon the great abundance of mosquitoes in Lapland

and the torments they inflicted upon man and beast. He states that he

believes that nowhere else on earth are they found in such abundance and

he compares their numbers to the dust of the earth. Even in the open,

you cannot draw your breath without having your mouth and nostrils

filled with them; and ointments of tar and cream or of fish grease are

scarcely sufficient to protect even the case-hardened cuticle of the

Laplander from their bite. Even in their cabins, the natives cannot take

a mouthful of food or lie down to sleep unless they are fumigated almost

to suffocation." In some parts of the Northwestern and Southwestern

United States it is necessary to protect horses working in the fields by

the use of sheets or burlaps, against the ferocious attacks of these

insects. It is a surprising fact that even in the dry deserts of the

western United States they sometimes occur in enormous numbers.

Until comparatively recent years, but few species of mosquitoes were

known and most of the statements regarding their life-history were based

upon the classic work of Reaumur (1738) on the biology of the rain

barrel mosquito, _Culex pipiens_. In 1896, Dr. Howard refers to

twenty-one species in the United States, now over fifty are known;

Giles, in 1900, gives a total of two hundred and forty-two for the world

fauna, now over seven hundred species are known. We have found eighteen

species at Ithaca, N. Y.

All of the known species of mosquitoes are aquatic in the larval stage,

but in their life-histories and habits such great differences occur that

we now know that it is not possible to select any one species as typical

of the group. For our present purpose we shall first discuss the general

characteristics and structure of mosquitoes, and shall then give the

life-history of a common species, following this by a brief

consideration of some of the more striking departures from what have

been supposed to be the typical condition.

The CULICIDAE are slender, nematocerous Diptera with narrow wings,

antennae plumose in the males, and usually with the proboscis much longer

than the head, slender, firm and adapted for piercing in the female.

The most characteristic feature is that the margins of the wings and, in

most cases, the wing veins possess a fringe of scale-like hairs. These

may also cover in part, or entirely, the head, thorax, abdomen and legs.

The females, only, suck blood.

On account of the importance of the group in this country and the

desirability of the student being able to determine material in various

stages, we show in the accompanying figures the characters most used in

classification.

The larvae (fig. 73) are elongate, with the head and thorax sharply

distinct. The larval antennae are prominent, consisting of a single

cylindrical and sometimes curved segment. The outer third is often

narrower and bears at its base a fan-shaped tuft of hairs, the

arrangement and abundance of which is of systematic importance. About

the mouth are the so-called rotary mouth brushes, dense masses of long

hairs borne by the labrum and having the function of sweeping food into

the mouth. The form and arrangement of thoracic, abdominal, and anal

tufts of hair vary in different species and present characteristics of

value. On either side of the eighth abdominal segment is a patch of

scales varying greatly in arrangement and number and of much value in

separating species. Respiration is by means of tracheae which open at the

apex of the so-called anal siphon, when it is present. In addition,

there are also one or two pairs of tracheal gills which vary much in

appearance in different species. On the ventral side of the anal siphon

is a double row of flattened, toothed spines whose number and shape are

likewise of some value in separating species. They constitute the comb

or pecten.

[Illustration: 73. Culex larva showing details of external structure.]

The pupa (fig. 139, b) unlike that of most insects, is active, though it

takes no food. The head and thorax are not distinctly separated, but the

slender flexible abdomen in sharply marked off. The antennae,

mouth-parts, legs, and wings of the future adult are now external, but

enclosed in chitinous cases. On the upper surface, near the base of the

wings are two trumpets, or breathing tubes, for the pupal spiracles are

towards the anterior end instead of at the caudal end, as in the larva.

At the tip of the abdomen is a pair of large chitinous swimming paddles.

As illustrative of the life cycle of a mosquito we shall discuss the

development of a common house mosquito, _Culex pipiens_, often referred

to in the Northern United States as the rain barrel mosquito. Its life

cycle is often given as typical for the entire group, but, as we have

already emphasized, no one species can serve this purpose.

The adults of _Culex pipiens_ hibernate throughout the winter in

cellars, buildings, hollow trees, or similar dark shelters. Early in the

spring they emerge and deposit their eggs in a raft-like mass. The

number of eggs in a single mass is in the neighborhood of two hundred,

recorded counts varying considerably. A single female may deposit

several masses during her life time. The duration of the egg stage is

dependent upon temperature. In the warm summer time the larvae may emerge

within a day. The larvae undergo four molts and under optimum conditions

may transform into pupae in about a week's time. Under the same favorable

conditions, the pupal stage may be completed in a day's time. The total

life cycle of _Culex pipiens_, under optimum conditions, may thus be

completed in a week to ten days. This period may be considerably

extended under less favorable conditions of temperature and food supply.

_Culex pipiens_ breeds continuously throughout the summer, developing in

rain barrels, horse troughs, tin cans, or indeed in any standing water

about houses, which lasts for a week or more. The catch basins of sewers

furnish an abundant supply of the pests under some conditions. Such

places, the tin gutters on residences, and all possible breeding places

must be considered in attempts to exterminate this species.

Other species of mosquitoes may exhibit radical departures from _Culex

pipiens_ in life-history and habits. To control them it is essential

that the biological details be thoroughly worked out for, as Howard,

Dyar, and Knab have emphasized, "much useless labor and expense can be

avoided by an accurate knowledge of the habits of the species." For a

critical discussion of the known facts the reader is referred to their

monograph. We shall confine ourselves to a few illustrations.

The majority of mosquitoes in temperate climates hibernate in the egg

stage, hatching in the spring or even mild winter days in water from

melting snow. It is such single-brooded species which appear in

astounding numbers in the far North. Similarly, in dry regions the eggs

may stand thorough dessication, and yet hatch out with great promptness

when submerged by the rains. "Another provision to insure the species

against destruction in such a case, exists in the fact * * * that not

all the eggs hatch, a part of them lying over until again submerged by

subsequent rains." In temperate North America, a few species pass the

winter in the larval state. An interesting illustration of this is

afforded by _Wyeomia smithii_, whose larvae live in pitcher plants and

are to be found on the coldest winter days imbedded in the solid ice.

Late in the spring, the adults emerge and produce several broods during

the summer.

In the United States, one of the most important facts which has been

brought out by the intensive studies of recent years is that certain

species are migratory and that they can travel long distances and become

an intolerable pest many miles from their breeding places. This was

forcibly emphasized in Dr. Smith's work in New Jersey, when he found

that migratory mosquitoes, developing in the salt marshes along the

coast, are the dominant species largely responsible for the fame of the

New Jersey mosquito. The species concerned are _Aedes sollicitans_, _A.

cantator_ and _A. taeniorhynchus_. Dr. Smith decided that the first of

these might migrate at least forty miles inland. It is obvious that

where such species are the dominant pest, local control measures are a

useless waste of time and money. Such migratory habits are rare,

however, and it is probable that the majority of mosquitoes do not fly

any great distance from their breeding places.

While mosquitoes are thought of primarily as a pest of man, there are

many species which have never been known to feed upon human or mammalian

blood, no matter how favorable the opportunity. According to Howard,

Dyar, and Knab, this is true of _Culex territans_, one of the common

mosquitoes in the summer months in the Northern United States. There are

some species, probably many, in which the females, like the males, are

plant feeders. In experimental work, both sexes are often kept alive for

long periods by feeding them upon ripe banana, dried fig, raisins, and

the like, and in spite of sweeping assertions that mosquitoes must have

a meal of blood in order to stimulate the ovaries to development, some

of the common blood-sucking species, notably _Culex pipiens_, have been

bred repeatedly without opportunity to feed upon blood.

The effect of the bite varies greatly with different species and depends

upon the susceptibility of the individual bitten. Some persons are

driven almost frantic by the attacks of the pests when their companions

seem almost unconscious of any inconvenience. Usually, irritation and

some degree of inflammation appear shortly following the bite. Not

infrequently a hardened wheal or even a nodule forms, and sometimes

scratching leads to secondary infection and serious results.

The source of the poison is usually supposed to be the salivary glands

of the insect. As we have already pointed out, (p. 34), Macloskie

believed that one lobe of the gland, on each side, was specialized for

forming the poison, while a radically different view is that of

Schaudinn, who believed that the irritation is due to the expelled

contents of the oesophageal diverticula, which contain a gas and a

peculiar type of fungi or bacteria. In numerous attempts, Schaudinn was

unable to produce any irritation by applying the triturated salivary

glands to a wound, but obtained the typical result when he used the

isolated diverticula.

The irritation of the bite may be relieved to some extent by using

ammonia water, a one per cent. alcoholic solution of menthol, or

preparations of cresol, or carbolic acid. Dr. Howard recommends rubbing

the bite gently with a piece of moist toilet soap. Castellani and

Chalmers recommend cleansing inflamed bites with one in forty carbolic

lotion, followed by dressing with boracic ointment. Of course,

scratching should be avoided as much as possible.

Repellents of various kinds are used, for warding off the attacks of the

insects. We have often used a mixture of equal parts of oil of

pennyroyal and kerosene, applied to the hands and face. Oil of

citronella is much used and is less objectionable to some persons. A

recommended formula is, oil of citronella one ounce, spirits of camphor

one ounce, oil of cedar one-half ounce. A last resort would seem to be

the following mixture recommended by Howard, Dyar, and Knab for use by

hunters and fishermen in badly infested regions, against mosquitoes and

blackflies.

Take 2-1/4 lbs. of mutton tallow and strain it. While still hot add 1/2

lb. black tar (Canadian tar). Stir thoroughly and pour into the

receptacle in which it is to be contained. When nearly cool stir in

three ounces of oil of citronella and 1-1/4 oz. of pennyroyal.

At night the surest protection is a good bed net. There are many types

of these in use, but in order to be serviceable and at the same time

comfortable it should be roomy and hung in such a way as to be stretched

tightly in every direction. We prefer one suspended from a broad, square

frame, supported by a right-angled standard which is fastened to the

head of the bed. It must be absolutely free from rents or holes and

tucked in securely under the mattress or it will serve merely as a

convenient cage to retain mosquitoes which gain an entrance. While such

nets are a convenience in any mosquito ridden community, they are

essential in regions where disease-carrying species abound. Screening of

doors, windows and porches, against the pests is so commonly practiced

in this country that its importance and convenience need hardly be

urged.

Destruction of mosquitoes and prevention of breeding are of fundamental

importance. Such measures demand first, as we have seen, the correct

determination of the species which is to be dealt with, and a knowledge

of its life-history and habits. If it prove to be one of the migratory

forms, it is beyond mere local effort and becomes a problem demanding

careful organization and state control. An excellent illustration of the

importance and effectiveness of work along these lines is afforded by

that in New Jersey, begun by the late Dr. John B. Smith and being pushed

with vigor by his successor, Dr. Headlee.

In any case, there is necessity for community action. Even near the

coast, where the migratory species are dominant, there are the local

species which demand attention and which cannot be reached by any

measures directed against the species of the salt marshes. The most

important of local measures consist in the destruction of breeding

places by filling or draining ponds and pools, clearing up of more

temporary breeding places, such as cans, pails, water barrels and the

like. Under conditions where complete drainage of swamps is

impracticable or undesirable, judicious dredging may result in a pool or

series of steep-sided pools deep enough to maintain a supply of fish,

which will keep down the mosquito larvae. Where water receptacles are

needed for storage of rain water, they should be protected by careful

screening or a film of kerosene over the top of the water, renewed every

two weeks or so, so as to prevent mosquitoes from depositing their eggs.

When kerosene is used, Water drawn from the bottom of the receptacle

will not be contaminated by it to any injurious extent. Where ponds

cannot be drained much good will be accomplished by spraying kerosene

oil on the surface of the water, or by the introduction of fish which

will feed on the larvae.

Detailed consideration of the most efficient measures for controlling

mosquitoes is to be found in Dr. Howard's Bulletin No. 88 of the Bureau

of Entomology, "Preventive and remedial work against mosquitoes" or, in

more summarized form, in Farmers' Bulletin No. 444. One of these should

be obtained by any person interested in the problems of mosquito control

and public health.

[Illustration: 74. Mouth parts of Simulium. After Grunberg.]

The Simuliidae, or Black Flies

The SIMULIIDAE, or black flies, are small, dark, or black flies, with a

stout body and a hump-back appearance. The antennae are short but

eleven-segmented, the wings broad, without scales or hairs, and with the

anterior veins stout but the others very weak. The mouth-parts (fig. 74)

are fitted for biting.

The larvae of the Simuliidae (fig. 75) are aquatic and, unlike those of

mosquitoes, require a well aerated, or swiftly running water. Here they

attach to stones, logs, or vegetation and feed upon various

micro-organisms. They pupate in silken cocoons open at the top. Detailed

life-histories have not been worked out for most of the species. We

shall consider as typical that of _Simulium pictipes_, an inoffensive

species widely distributed in the Eastern United States, which has been

studied especially at Ithaca, N.Y. (Johannsen, 1903).

[Illustration: 75. Larva of Simulium, (x8). After Garman.]

The eggs are deposited in a compact yellowish layer on the surface of

rock, on the brinks of falls and rapids where the water is flowing

swiftly. They are elongate ellipsoidal in shape, about .4 by .18 mm. As

myriads of females deposit in the same place the egg patches may be

conspicuous coatings of a foot or much more in diameter. When first laid

they are enveloped in a yellowish white slime, which becomes darker,

until finally it becomes black just before the emerging of the larvae.

The egg stage lasts a week.

The larvae (fig. 75) are black, soft skinned, somewhat cylindrical in

shape, enlarged at both ends and attenuated in the middle. The posterior

half is much stouter than the anterior part and almost club-shaped. The

head bears two large fan-shaped organs which aid in procuring food.

Respiration is accomplished by means of three so-called blood gills

which are pushed out from the dorsal part of the rectum. The larvae occur

in enormous numbers, in moss-like patches. If removed from their natural

habitat and placed in quiet water they die within three or four hours.

Fastened to the rock by means of a disk-like sucker at the caudal end of

the body, they ordinarily assume an erect position. They move about on

the surface of the rocks, to a limited extent, with a looping gait

similar to that of a measuring worm, and a web is secreted which

prevents their being washed away by the swiftly flowing water. They feed

chiefly upon algae and diatoms.

The complete larval stage during the summer months occupies about four

weeks, varying somewhat with the temperature and velocity of the water.

At the end of this period they spin from cephalic glands, boot-shaped

silken cocoons within which they pupate. The cocoon when spun is firmly

attached to the rock and also to adjacent cocoons. Clustered

continuously over a large area and sometimes one above another, they

form a compact, carpet-like covering on the rocks, the reddish-brown

color of which is easily distinguishable from the jet-black appearance

of the larvae. The pupal stage lasts about three weeks. The adult fly,

surrounded by a bubble of air, quickly rises to the surface of the water

and escapes. The adults (fig. 76) are apparently short lived and thus

the entire life cycle, from egg to egg is completed in approximately

eight weeks.

[Illustration: 76. Simulium venustum, (x8). After Garman.]

In the case of _Simulium pictipes_ at Ithaca, N. Y., the first brood of

adults emerges early in May and successive generations are produced

throughout the summer and early autumn. This species winters in the

larval condition. Most of the other species of _Simulium_ which have

been studied seem to be single brooded.

While _Simulium pictipes_ does not attack man, there are a number of the

species which are blood-sucking and in some regions they are a veritable

scourge. In recent years the greatest interest in the group has been

aroused by Sambon's hypothesis that they transmit pellagra from man to

man. This has not been established, and, indeed, seems very doubtful,

but the importance of these insects as pests and the possibility that

they may carry disease make it urgent that detailed life-histories of

the hominoxious species be worked out.

As pests a vivid account of their attacks is in Agassiz's "Lake

Superior" (p. 61), quoted by Forbes (1912).

"Neither the love of the picturesque, however, nor the interests of

science, could tempt us into the woods, so terrible were the black

flies. This pest of flies which all the way hither had confined our

ramblings on shore pretty closely to the rocks and the beach, and had

been growing constantly worse, here reached its climax. Although

detained nearly two days, * * * we could only sit with folded hands, or

employ ourselves in arranging specimens, and such other operations as

could be pursued in camp, and under the protection of a 'smudge.' One,

whom scientific ardor tempted a little way up the river in a canoe,

after water plants, came back a frightful spectacle, with blood-red

rings round his eyes, his face bloody, and covered with punctures. The

next morning his head and neck were swollen as if from an attack of

erysipelas."

There are even well authenticated accounts on record of death of humans

from the attacks of large swarms of these gnats. In some regions, and

especially in the Mississippi Valley in this country, certain species of

black flies have been the cause of enormous losses to farmers and

stockmen, through their attacks on poultry and domestic animals. C. V.

Riley states that in 1874 the loss occasioned in one county in Tennessee

was estimated at $500,000.

The measures of prevention and protection against these insects have

been well summarized by Forbes (1912). They are of two kinds: "the use

of repellents intended to drive away the winged flies, and measures for

the local destruction of the aquatic larvae. The repellents used are

either smudges, or surface applications made to keep the flies from

biting. The black-fly will not endure a dense smoke, and the well-known

mosquito smudge seems to be ordinarily sufficient for the protection of

man. In the South, leather, cloth, and other materials which will make

the densest and most stifling smoke, are often preserved for this use in

the spring. Smudges are built in pastures for the protection of stock,

and are kept burning before the doors of barns and stables. As the

black-flies do not readily enter a dark room, light is excluded from

stables as much as possible during the gnat season. If teams must be

used in the open field while gnats are abroad, they may be protected

against the attacks of the gnats by applying cotton-seed oil or axle

grease to the surface, especially to the less hairy parts of the

animals, at least twice a day. A mixture of oil and tar and, indeed,

several other preventives, are of practical use in badly infested

regions; but no definite test or exact comparison has been made with any

them in a way to give a record of the precise results."

"It is easy to drive the flies from houses or tents by burning pyrethrum

powder inside; this either kills the flies or stupifies them so that

they do not bite for some time thereafter." * * * "Oil of tar is

commonly applied to the exposed parts of the body for the purpose of

repelling the insects, and this preparation is supplied by the Hudson

Bay Company to its employees. Minnesota fishermen frequently grease

their faces and hands with a mixture of kerosene and mutton tallow for

the same purpose." We have found a mixture of equal parts of kerosene

and oil of pennyroyal efficient.

Under most circumstances very little can be done to destroy this insect

in its early stage, but occasionally conditions are such that a

larvicide can be used effectively. Weed (1904), and Sanderson (1910)

both report excellent results from the use of phinotas oil, a

proprietary compound. The first-mentioned also found that in some places

the larvae could be removed by sweeping them loose in masses with stiff

stable brooms and then catching them downstream on wire netting

stretched in the water.

Chironomidae or Midges

The flies of this family, commonly known as midges, resemble mosquitoes

in form and size but are usually more delicate, and the wing-veins,

though sometimes hairy, are not fringed with scales. The venation is

simpler than in the mosquitoes and the veins are usually less distinct.

These midges, especially in spring or autumn, are often seen in immense

swarms arising like smoke over swamps and producing a humming noise

which can be heard for a considerable distance. At these seasons they

are frequently to be found upon the windows of dwellings, where they are

often mistaken for mosquitoes.

The larvae are worm-like, but vary somewhat in form in the different

genera. Most of them are aquatic, but a few live in the earth, in

manure, decaying wood, under bark, or in the sap of trees, especially in

the sap which collects in wounds.

[Illustration: 77. Culicoides guttipennis; (_a_) adult, (x15); (_b_)

head of same; (_c_) larva; (_d_) head; (_e_) pupa. After Pratt.]

Of the many species of CHIRONOMIDAE, (over eight hundred known), the vast

majority are inoffensive. The sub-family Ceratopogoninae, however, forms

an exception, for some of the members of this group, known as sandflies,

or punkies, suck blood and are particularly troublesome in the

mountains, along streams, and at the seashore. Most of these have been

classed under the genus _Ceratopogon_, but the group has been broken up

into a number of genera and _Ceratopogon_, in the strict sense, is not

known to contain any species which sucks the blood of vertebrates.

THE CERATOPOGONINAE--The Ceratopogoninae are among the smallest of the

Diptera, many of them being hardly a millimeter long and some not even

so large. They are Chironomidae in which the thorax is not prolonged over

the head. The antennae are filiform with fourteen (rarely thirteen)

segments in both sexes, those of the male being brush-like. The basal

segment is enlarged, the last segment never longer than the two

preceding combined, while the last five are sub-equal to, or longer than

the preceding segment. The legs are relatively stouter than in the other

Chironomidae. The following three genera of this subfamily are best known

as blood suckers in this country.

Of the genus _Culicoides_ there are many species occurring in various

parts of the world. A number are known to bite man and animals and it is

probable that all are capable of inflicting injury. In some localities

they are called punkies, in others, sand-flies, a name sometimes also

applied to the species of _Simulium_ and _Phlebotomus_. Owing to their

very small size they are known by some tribes of Indians as No-see-ums.

The larvae are found in ponds, pools, water standing in hollow tree

stumps, and the like. Though probably living chiefly in fresh water, we

have found a species occurring in salt water. The larvae are small,

slender, legless, worm-like creatures (fig. 77_c_) with small brown head

and twelve body segments. The pupae (fig. 77_e_) are slender, more

swollen at the anterior end and terminating in a forked process. They

float nearly motionless in a vertical position, the respiratory tubes in

contact with the surface film. The adults are all small, rarely

exceeding 2-1/4 mm. in length. The wings are more or less covered with

erect setulae or hairs and in many species variously spotted and marked

with iridescent blotches. The antennae have fourteen segments, the palpi

usually five. The wing venation and mouth-parts are shown in figures 77

and 78. Of the twenty or more species of this genus occurring in the

United States the following are known to bite: _C. cinctus_, _C.

guttipennis_, _C. sanguisuga_, _C. stellifer_, _C. variipennis_, _C.

unicolor_.

[Illustration: 78. Culicoides guttipennis; mouth parts of adult. After

Pratt.]

One of the most widely distributed and commonest species in the Eastern

States is _C. guttipennis_ (fig. 77a). It is black with brown legs, a

whitish ring before the apex of each femur and both ends of each tibia;

tarsi yellow, knobs of halteres yellow. Mesonotum opaque, brown, two

vittae in the middle, enlarging into a large spot on the posterior half,

also a curved row of three spots in front of each wing, and the narrow

lateral margins, light gray pruinose. Wings nearly wholly covered with

brown hairs, gray, with markings as shown in the figure. Length one mm.

_Johannseniella_ Will. is a wide-spread genus related to the foregoing.

Its mouth-parts are well adapted for piercing and it is said to be a

persistent blood sucker, particularly in Greenland. This genus is

distinguished from _Culicoides_ by its bare wings, the venation (fig.

163, c), and the longer tarsal claws. There are over twenty North

American species.

[Illustration: 79. Chrysops univittatus, (x4). After Osborn.]

In the Southwestern United States, _Tersesthes torrens_ Towns. occurs, a

little gnat which annoys horses, and perhaps man also, by its bite. It

is related to _Culicoides_ but differs in the number of antennal

segments and in its wing venation (fig. 163, e). The fly measures but

two mm. in length and is blackish in color. The antennae of the female

have thirteen segments, the palpi but three, of which the second is

enlarged and swollen.

Tabanidae or Horse-Flies

The TABANIDAE,--horse-flies, ear-flies, and deer-flies,--are well-known

pests of cattle and horses and are often extremely annoying to man. The

characteristics of the family and of the principal North American genera

are given in the keys of Chapter XII. There are over 2500 recorded

species. As in the mosquitoes, the females alone are blood suckers. The

males are flower feeders or live on plant juices. This is apparently

true also of the females of some of the genera.

The eggs are deposited in masses on water plants or grasses and sedges

growing in marshy or wet ground. Those of a common species of _Tabanus_

are illustrated in figure 80, _a_. They are placed in masses of several

hundred, light colored when first deposited but turning black. In a week

or so the cylindrical larvae, tapering at both ends (fig. 80, _b_),

escape to the water, or damp earth, and lead an active, carnivorous

life, feeding mainly on insect larvae, and worms. In the forms which have

been best studied the larval life is a long one, lasting for months or

even for more than a year. Until recently, little was known concerning

the life-histories of this group, but the studies of Hart (1895), and

Hine (1903 +) have added greatly to the knowledge concerning North

American forms.

Many of the species attack man with avidity and are able to inflict

painful bites, which may smart for hours. In some instances the wound is

so considerable that blood will continue to flow after the fly has left.

We have seen several cases of secondary infection following such bites.

[Illustration: 80. (_a_) Eggs of Tabanus. Photograph by J. T. Lloyd.]

[Illustration: 80. (_b_) Larva of Tabanus. Photograph by M. V. S.]

The horse-flies have been definitely convicted of transferring the

trypanosome of surra from diseased to healthy animals and there is good

evidence that they transfer anthrax. The possibility of their being

important agents in the conveyal of human diseases should not be

overlooked. Indeed, Leiper has recently determined that a species of

_Chrysops_ transfers the blood parasite _Filaria diurna_.

Leptidae or Snipe-Flies

The family LEPTIDAE is made up of moderate or large sized flies,

predaceous in habit. They are sufficiently characterized in the keys of

Chapter XII. Four blood-sucking species belonging to three genera have

been reported. Of these _Symphoromyia pachyceras_ is a western species.

Dr. J. C. Bradley, from personal experience, reports it as a vicious

biter.

[Illustration: 80. (_c_) Mouth parts of Tabanus. After Grunberg.]

Oestridae or Bot-flies

To the family OESTRIDAE belong the bot and warble-flies so frequently

injurious to animals. The adults are large, or of medium size, heavy

bodied, rather hairy, and usually resemble bees in appearance.

The larvae live parasitically in various parts of the body of mammals,

such as the stomach (horse bot-fly), the subcutaneous connective tissue

(warble-fly of cattle), or the nasal passage (sheep bot-fly or head

maggot).

There are on record many cases of the occurrence of the larvae of

Oestridae as occasional parasites of man. A number of these have been

collected and reviewed in a thesis by Mme. Petrovskaia (1910). The

majority of them relate to the following species.

_Gastrophilus haemorrhoidalis_, the red tailed bot-fly, is one of the

species whose larvae are most commonly found in the stomach of the horse.

Schoch (1877) cites the case of a woman who suffered from a severe case

of chronic catarrh of the stomach, and who vomited, and also passed from

the anus, larvae which apparently belonged to this species. Such cases

are exceedingly rare but instances of subcutaneous infestation are

fairly numerous. In the latter type these larvae are sometimes the cause

of the peculiar "creeping myasis." This is characterized at its

beginning by a very painful swelling which gradually migrates, producing

a narrow raised line four to twenty-five millimeters broad. When the

larva is mature, sometimes after several months, it becomes stationary

and a tumor is formed which opens and discharges the larva along with

pus and serum.

_Gastrophilus equi_ is the most widespread and common of the horse

bot-flies. Portschinsky reports it as commonly causing subcutaneous

myasis of man in Russia.

_Hypoderma bovis_ (= _Oestrus bovis_), and _Hypoderma lineata_ are the

so-called warble-flies of cattle. The latter species is the more common

in North America but Dr. C. G. Hewitt has recently shown that _H. bovis_

also occurs. Though warbles are very common in cattle in this country,

the adult flies are very rarely seen. They are about half an inch in

length, very hairy, dark, and closely resemble common honey-bees.

They deposit their eggs on the hairs of cattle and the animals in

licking themselves take in the young larvae. These pass out through the

walls of the oesophagus and migrate through the tissues of the animal,

to finally settle down in the subcutaneous tissue of the back. The

possibility of their entering directly through the skin, especially in

case of infestation of man, is not absolutely precluded, although it is

doubtful.

For both species of _Hypoderma_ there are numerous cases on record of

their occurrence in man. Hamilton (1893) saw a boy, six years of age,

who had been suffering for some months from the glands on one side of

his neck being swollen and from a fetid ulceration around the back teeth

of the lower jaw of the same side. Three months' treatment was of no

avail and the end seemed near; one day a white object, which was seen to

move, was observed in the ulcer at the root of the tongue, and on being

extracted was recognized as a full grown larva of _Hypoderma_. It was of

usual tawny color, about half an inch long when contracted, about one

third that thickness, and quite lively. The case resulted fatally. The

boy had been on a dairy farm the previous fall, where probably the egg

(or larva) was in some way taken into his mouth, and the larva found

between the base of the tongue and the jaw suitable tissue in which to

develop.

Topsent (1901) reports a case of "creeping myasis" caused by _H.

lineata_ in the skin of the neck and shoulders of a girl eight years of

age. The larva travelled a distance of nearly six and a half inches. The

little patient suffered excruciating pain in the place occupied by the

larva.

_Hypoderma diana_ infests deer, and has been known to occur in man.

_Oestris ovis_, the sheep bot-fly, or head maggot, is widely distributed

in all parts of the world. In mid-summer the flies deposit living

maggots in the nostrils of sheep. These larvae promptly pass up the nasal

passages into the frontal and maxillary sinuses, where they feed on the

mucous to be found there. In their migrations they cause great

irritation to their host, and when present in numbers may cause vertigo,

paroxysms, and even death. Portschinsky in an important monograph on

this species, has discussed in detail its relation to man. He shows that

it is not uncommon for the fly to attack man and that the minute living

larvae are deposited in the eyes, nostrils, lips, or mouth. A typical

case in which the larvae were deposited in the eye was described by a

German oculist Kayser, in 1905. A woman brought her six year old

daughter to him and said that the day before, about noontime, a flying

insect struck the eye of the child and that since then she had felt a

pain which increased towards evening. In the morning the pain ceased but

the eye was very red. She was examined at about noon, at which time she

was quiet and felt no pain. She was not sensitive to light, and the only

thing noticed was a slight congestion and accumulation of secretion in

the corner of the right eye. A careful examination of the eye disclosed

small, active, white larvae that crawled out from the folds of the

conjunctiva and then back and disappeared. Five of these larvae were

removed and although an uncomfortable feeling persisted for a while, the

eye became normal in about three weeks.

Some of the other recorded cases have not resulted so favorably, for the

eyesight has been seriously affected or even lost.

According to Edmund and Etienne Sergent (1907), myasis caused by the

larvae of _Oestris ovis_ is very common among the shepherds in Algeria.

The natives say that the fly deposits its larvae quickly, while on the

wing, without pause. The greatest pain is caused when these larvae

establish themselves in the nasal cavities. They then produce severe

frontal headaches, making sleep impossible. This is accompanied by

continuous secretion from the nasal cavities and itching pains in the

sinuses. If the larvae happen to get into the mouth, the throat becomes

inflamed, swallowing is painful, and sometimes vomiting results. The

diseased condition may last for from three to ten days or in the case of

nasal infection, longer, but recovery always follows. The natives remove

the larvae from the eye mechanically by means of a small rag. When the

nose is infested, tobacco fumigations are applied, and in case of throat

infestation gargles of pepper, onion, or garlic extracts are used.

_Rhinoestrus nasalis_, the Russian gad-fly, parasitizes the

nasopharyngeal region of the horse. According to Portschinsky, it not

infrequently attacks man and then, in all the known cases deposits its

larvae in the eye, only. This is generally done while the person is

quiet, but not during sleep. The fly strikes without stopping and

deposits its larva instantaneously. Immediately after, the victim

experiences lancinating pains which without intermission increase in

violence. There is an intense conjunctivitis and if the larvae are not

removed promptly the envelopes of the eye are gradually destroyed and

the organ lost.

[Illustration: 81. Larvae of Dermatobia cyaniventris. After Blanchard.]

[Illustration: 82. Young larva of Dermatobia cyaniventris. After

Surcouf.]

_Dermatobia cyaniventris_--This fly (fig. 83) is widely distributed

throughout tropical America, and in its larval stage is well known as a

parasite of man. The larvae (figs. 81 and 82) which are known as the "ver

macaque," "torcel," "ver moyocuil" or by several other local names,

enter the skin and give rise to a boil-like swelling, open at the top,

and comparable with the swelling produced by the warble fly larvae, in

cattle. They cause itching and occasional excruciating pain. When

mature, nearly an inch in length, they voluntarily leave their host,

drop to the ground and complete their development. The adult female is

about 12 mm. in length. The face is yellow, the frons black with a

grayish bloom; antennae yellow, the third segment four times as long as

the second, the arista pectinate. The thorax is bluish black with

grayish bloom; the abdomen depressed, brilliant metallescent blue with

violet tinge. The legs are yellowish, the squamae and wings brownish.

The different types of larvae represented in figure 81 were formerly

supposed to belong to different species but Blanchard regards them as

merely various stages of the same species. It is only very recently that

the early stage and the method by which man becomes infested were made

known.

[Illustration: 83. Dermatobia cyaniventris (x1-3/4). After Manson.]

[Illustration: 84. Mosquito carrying eggs of Dermatobia cyaniventris.

After Surcouf.]

About 1900, Blanchard observed the presence of packets of large-sized

eggs under the abdomen of certain mosquitoes from Central America; and

in 1910, Dr. Morales, of Costa Rica, declared that the Dermatobia

deposited its eggs directly under the abdomen of the mosquito and that

they were thus carried to vertebrates. Dr. Nunez Tovar observed the

mosquito carriers of the eggs and placing larvae from this source on

animals, produced typical tumors and reared the adult flies. It remained

for Surcouf (1913) to work out the full details. He found that the

Dermatobia deposits its eggs in packets covered by a very viscid

substance, on leaves. These become attached to mosquitoes of the species

_Janthinosoma lutzi_ (fig. 84) which walk over the leaves. The eggs

which adhere to the abdomen, remain attached and are thus transported.

The embryo develops, but the young larva (fig. 82) remains in the egg

until it has opportunity to drop upon a vertebrate fed upon by the

mosquito.

Muscidae

The following MUSCIDAE, characterized elsewhere, deserve special mention

under our present grouping of parasitic species. Other important species

will be considered as facultative parasites.

_Stomoxys calcitrans_, the stable-fly, or the biting house-fly, is often

confused with _Musca domestica_ and therefore is discussed especially in

our consideration of the latter species as an accidental carrier of

disease. Its possible relation to the spread of infantile paralysis is

also considered later.

The _tsetse flies_, belonging to the genus _Glossina_, are African

species of blood-sucking Muscidae which have attracted much attention

because of their role in transmitting various trypanosome diseases of

man and animals. They are characterized in Chapter XII and are also

discussed in connection with the diseases which they convey.

_Chrysomyia macellaria_, (= _Compsomyia_), the "screw worm"-fly is one

of the most important species of flies directly affecting man, in North

America. It is not normally parasitic, however, and hence will be

considered with other facultative parasites in Chapter IV.

[Illustration: 85. Larva of Auchmeromyia luteola. After Graham-Smith.]

[Illustration: 86. Auchmeromyia luteola (x4). After Graham-Smith.]

_Auchmeromyia luteola_, the Congo floor maggot. This is a muscid of

grewsome habits, which has a wide distribution throughout Africa. The

fly (fig. 86) deposits its eggs on the ground of the huts of the

natives. The whitish larvae (fig. 85) on hatching are slightly flattened

ventrally, and each segment bears posteriorly three foot-pads

transversely arranged. At night the larvae find their way into the low

beds or couches of the natives and suck their blood. The adult flies do

not bite man and, as far as known, the larvae do not play any role in the

transmission of sleeping sickness or other diseases.

This habit of blood-sucking by muscid larvae is usually referred to as

peculiar to _Auchmeromyia luteola_ but it should be noted that the larvae

of _Protocalliphora_ frequent the nests of birds and feed upon the

young. Mr. A. F. Coutant has studied especially the life-history and

habits of _P. azurea_, whose larvae he found attacking young crows at

Ithaca, N.Y. He was unable to induce the larvae to feed on man.

[Illustration: 87. Cordylobia anthropophaga (x3). After Fulleborn.]

[Illustration: 88. Larva of Cordylobia anthropophaga. After Blanchard.]

_Cordylobia anthropophaga_, (_Ochromyia anthropophaga_), or Tumbu-fly

(fig. 87) is an African species whose larvae affect man much as do those

of _Dermatobia cyniventris_, of Central and South America. The larva

(fig. 88), which is known as "ver du Cayor" because it was first

observed in Cayor, in Senegambia, develops in the skin of man and of

various animals, such as dogs, cats, and monkeys. It is about 12 mm. in

length, and of the form of the larvae of other muscids. Upon the

intermediate segments are minute, brownish recurved spines which give to

the larva its characteristic appearance. The life-history is not

satisfactorily worked out, but Fuller (1914), after reviewing the

evidence believes that, as a rule, it deposits its young in the sleeping

places of man and animals, whether such be a bed, a board, the floor, or

the bare ground. In the case of babies, the maggots may be deposited on

the scalp. The minute maggots bore their way painlessly into the skin.

As many as forty parasites have been found in one individual and one

author has reported finding more than three hundred in a spaniel puppy.

Though their attacks are at times extremely painful, it is seldom that

any serious results follow.

THE SIPHONAPTERA OR FLEAS

The SIPHONAPTERA, or fleas (fig. 89) are wingless insects, with highly

chitinized and laterally compressed bodies. The mouth-parts are formed

for piercing and sucking. Compound eyes are lacking but some species

possess ocelli. The metamorphosis is complete.

This group of parasites, concerning which little was known until

recently, has assumed a very great importance since it was learned that

fleas are the carriers of bubonic plague. Now over four hundred species

are known. Of these, several species commonly attack man. The most

common hominoxious species are _Pulex irritans_, _Xenopsylla cheopis_,

_Ctenocephalus canis_, _Ctenocephalus felis_, _Ceratophyllus fasciatus_

and _Dermatophilus penetrans_, but many others will feed readily on

human blood if occasion arises.

[Illustration: 89. Xenopsylla cheopis, male (x25). After Jordan and

Rothschild.]

We shall treat in this place of the general biology and habits of the

hominoxious forms and reserve for the systematic section the discussion

of the characteristics of the different genera.

The most common fleas infesting houses in the Eastern United States are

the cosmopolitan dog and cat fleas, _Ctenocephalus canis_ (fig. 90) and

_C. felis_. Their life cycles will serve as typical. These two species

have until recently been considered as one, under the name _Pulex

serraticeps_. See figure 92.

[Illustration: 90. Dog flea (x15). After Howard.]

The eggs are oval, slightly translucent or pearly white, and measure

about .5 mm. in their long diameter. They are deposited loosely in the

hairs of the host and readily drop off as the animal moves around.

Howard found that these eggs hatch in one to two days. The larvae are

elongate, legless, white, worm-like creatures. They are exceedingly

active, and avoid the light in every way possible. They cast their first

skin in from three to seven days and their second in from three to four

days. They commenced spinning in from seven to fourteen days after

hatching and the imago appeared five days later. Thus in summer, at

Washington, the entire life cycle may be completed in about two weeks.

(cf. fig. 91, 92).

Strickland's (1914) studies on the biology of the rat flea,

_Ceratophyllus fasciatus_, have so important a general bearing that we

shall cite them in considerable detail.

[Illustration: 91. Larva of Xenopsylla cheopis. After Bacot and

Ridewood.]

He found, to begin with, that there is a marked inherent range in the

rate of development. Thus, of a batch of seventy-three eggs, all laid in

the same day and kept together under the same conditions, one hatched in

ten days; four in eleven days; twenty-five in twelve days; thirty-one in

thirteen days; ten in fourteen days; one in fifteen days; and one in

sixteen days. Within these limits the duration of the egg period seems

to depend mainly on the degree of humidity. The incubation period is

never abnormally prolonged as in the case of lice, (Warburton) and

varying conditions of temperature and humidity have practically no

effect on the percentage of eggs which ultimately hatch.

The same investigator found that the most favorable condition for the

larva is a low temperature, combined with a high degree of humidity; and

that the presence of rubbish in which the larva may bury itself is

essential to its successful development. When larvae are placed in a

bottle containing either wood-wool soiled by excrement, or with feathers

or filter paper covered with dried blood they will thrive readily and

pupate. They seem to have no choice between dried blood and powdered rat

feces for food, and also feed readily on flea excrement. They possess

the curious habit of always devouring their molted skins.

[Illustration: 92. Head and pronotum of (_a_) dog flea; (_b_) of cat

flea; (_c_) of hen flea. After Rothschild. (_d_) Nycteridiphilus

(Ischnopsyllus) hexactenus. After Oudemans.]

An important part of Strickland's experiments dealt with the question of

duration of the pupal stage under the influence of temperature and with

the longevity and habits of the adult. In October, he placed a batch of

freshly formed cocoons in a small dish that was kept near a white rat in

a deep glass jar in the laboratory. Two months later one small and

feeble flea had emerged, but no more until February, four months after

the beginning of the experiment. Eight cocoons were then dissected and

seven more found to contain the imago fully formed but in a resting

state. The remainder of the batch was then placed at 70^o F. for one

night, near a white rat. The next day all the cocoons were empty and the

fleas were found on the white rat.

Thus, temperature greatly influences the duration of the pupal period,

which in _Ceratophyllus fasciatus_ averages seventeen days. Moreover,

when metamorphosis is complete a low temperature will cause the imago to

remain within the cocoon.

Sexually mature and ovipositing fleas, he fed at intervals and kept

alive for two months, when the experiment was discontinued. In the

presence of rubbish in which they could bury themselves, unfed rat fleas

were kept alive for many months, whereas in the absence of any such

substratum they rarely lived a month. In the former case, it was found

that the length of life is influenced to some degree by the temperature

and humidity. In an experiment carried out at 70^o F. and 45 per cent

humidity, the fleas did not live for more than four months, while in an

experiment at 60^o F. and 70 per cent humidity they lived for at least

seventeen months. There was no indication that fleas kept under these

conditions sucked moisture from surrounding objects, and those kept in

bell jars, with an extract of flea-rubbish on filter paper, did not live

any longer than those which were not so supplied.

Curiously enough, although the rat is the normal host of _Ceratophyllus

fasciatus_, it was found that when given the choice these fleas would

feed upon man in preference to rats. However, none of the fleas laid

eggs unless they fed on rat blood.

The experiments of Strickland on copulation and oviposition in the rat

flea showed that fleas do not copulate until they are sexually mature

and that, at least in the case of _Ceratophyllus fasciatus_, the

reproductive organs are imperfectly developed for some time (more than a

week) after emerging from the pupa. When mature, copulation takes place

soon after the fleas have fed on their true host--the rat--but not if

they have fed on a facultative host only, such as man. Copulation is

always followed by oviposition within a very short time.

The effect of the rat's blood on the female with regard to egg-laying,

Strickland concludes, is stimulating rather than nutritive, as fleas

that were without food for many months were observed to lay eggs

immediately after one feed. Similarly, the male requires the stimulus of

a meal of rat's blood before it displays any copulatory activity.

Mitzmain (1910) has described in detail the act of biting on man, as

observed in the squirrel flea, _Ceratophyllus acutus_. "The flea when

permitted to walk freely on the arm selects a suitable hairy space where

it ceases abruptly in its locomotion, takes a firm hold with the tarsi,

projects its proboscis, and prepares to puncture the skin. A puncture is

drilled by the pricking epipharynx, the saw-tooth mandibles

supplementing the movement by lacerating the cavity formed. The two

organs of the rostrum work alternately, the middle piece boring, while

the two lateral elements execute a sawing movement. The mandibles, owing

to their basal attachments, are, as is expressed by the advisory

committee on plague investigations in India (_Journal of Hygiene_, vol.

6, No. 4, p. 499), 'capable of independent action, sliding up and down

but maintaining their relative positions and preserving the lumen of the

aspiratory channel.' The labium doubles back, the V-shaped groove of

this organ guiding the mandibles on either side."

"The action of the proboscis is executed with a forward movement of the

head and a lateral and downward thrust of the entire body. As the

mouth-parts are sharply inserted, the abdomen rises simultaneously. The

hind and middle legs are elevated, resembling oars. The forelegs are

doubled under the thorax, the tibia and tarsi resting firmly on the

epidermis serve as a support for the body during the feeding. The

maxillary palpi are retracted beneath the head and thorax. The labium

continues to bend, at first acting as a sheath for the sawing mandibles,

and as these are more deeply inserted, it bends beneath the head with

the elasticity of a bow, forcing the mandibles into the wound until the

maxillae are embedded in the skin of the victim. When the proboscis is

fully inserted, the abdomen ceases for a time its lateral swinging."

"The acute pain of biting is first felt when the mandibles have not

quite penetrated and subsequently during each distinct movement of the

abdomen. The swinging of the abdomen gradually ceases as it becomes

filled with blood. The sting of the biting gradually becomes duller and

less sensitive as feeding progresses. The movements of the elevated

abdomen grow noticeably feebler as the downward thrusts of the springy

bow-like labium becomes less frequent."

"As the feeding process advances one can discern through the translucent

walls of the abdomen a constant flow of blood, caudally from the

pharynx, accompanied by a peristaltic movement. The end of the meal is

signified in an abrupt manner. The flea shakes its entire body, and

gradually withdraws its proboscis by lowering the abdomen and legs and

violently twisting the head."

"When starved for several days the feeding of the rat fleas is conducted

in a rather vigorous manner. As soon as the proboscis is buried to the

full length the abdomen is raised and there ensues a gradual lateral

swaying motion, increasing the altitude of the raised end of the abdomen

until it assumes the perpendicular. The flea is observed at this point

to gain a better foothold by advancing the fore tarsi, and then,

gradually doubling back the abdomen, it turns with extreme agility,

nearly touching with its dorsal side the skin of the hand upon which it

is feeding. Meanwhile, the hungry parasite feeds ravenously."

"It is interesting to note the peculiar nervous action which the rodent

fleas exhibit immediately when the feeding process is completed or when

disturbed during the biting. Even while the rostrum is inserted to the

fullest the parasite shakes its head spasmodically; in a twinkling the

mouth is withdrawn and then the flea hops away."

A habit of fleas which we shall see is of significance in considering

their agency in the spread of bubonic plague, is that of ejecting blood

from the anus as they feed.

Fleas are famous for their jumping powers, and in control measures it is

of importance to determine their ability along this line. It is often

stated that they can jump about four inches, or, according to the Indian

Plague Commission _Xenopsylla cheopis_ cannot hop farther than five

inches. Mitzmain (1910) conducted some careful experiments in which he

found that the human flea, _Pulex irritans_, was able to jump as far as

thirteen inches on a horizontal plane. The mean average of five

specimens permitted to jump at will was seven and three-tenths inches.

The same species was observed to jump perpendicularly to a height of at

least seven and three-fourths inches. Other species were not able to

equal this record.

The effect of the bite of fleas on man varies considerably according to

the individual susceptibility. According to Patton and Cragg, this was

borne out in a curious manner by the experiments of Chick and Martin.

"In these, eight human hosts were tried; in seven, little or no

irritation was produced, while in one quite severe inflammation was set

up around each bite." Of two individuals, equally accustomed to the

insects, going into an infested room, one may be literally tormented by

them while the other will not notice them. Indeed it is not altogether

a question of susceptibility, for fleas seem to have a special

predilection for certain individuals. The typical itching wheals

produced by the bites are sometimes followed, especially after

scratching, by inflammatory papules.

The itching can be relieved by the use of lotions of carbolic acid (2-3

per cent), camphor, menthol lotion, or carbolated vaseline. If forced to

sleep in an infested room, protection from attacks can be in a large

measure gained by sprinkling pyrethrum, bubach, or California insect

powder between the sheets. The use of camphor, menthol, or oil of

eucalyptus, or oil of pennyroyal is also said to afford protection to a

certain extent.

In the Eastern United States the occurrence of fleas as household pests

is usually due to infested cats and dogs which have the run of the

house. We have seen that the eggs are not attached to the host but drop

to the floor when they are laid. Verrill, cited by Osborn, states that

on one occasion he was able to collect fully a teaspoonful of eggs from

the dress of a lady in whose lap a half-grown kitten had been held for a

short time. Patton and Cragg record seeing the inside of a hat in which

a kitten had spent the night, so covered with flea eggs that it looked

"as if it had been sprinkled with sugar from a sifter." It is no wonder

that houses in which pets live become overrun with the fleas.

One of the first control measures, then, consists in keeping such

animals out of the house or in rigorously keeping them free from fleas.

The latter can best be accomplished by the use of strong tar soap or

Armour's "Flesope," which may be obtained from most druggists. The use

of a three per cent solution of creolin, approximately four teaspoonfuls

to a quart of warm water, has also been recommended. While this is

satisfactory in the case of dogs, it is liable to sicken cats, who will

lick their fur in an effort to dry themselves. Howard recommends

thoroughly rubbing into the fur a quantity of pyrethrum powder. This

partially stupifies the fleas which should be promptly swept up and

burned.

He also recommends providing a rug for the dog or cat to sleep on and

giving this rug a frequent shaking and brushing, afterwards sweeping up

and burning the dust thus removed.

Since the larvae of fleas are very susceptible to exposure, the use of

bare floors, with few rugs, instead of carpets or matting, is to be

recommended. Thorough sweeping, so as to allow no accumulation of dust

in cracks and crevices will prove efficient. If a house is once

infested it may be necessary to thoroughly scrub the floors with hot

soapsuds, or to spray them with gasoline. If the latter method is

adopted, care must be taken to avoid the possibility of fire.

To clear a house of fleas Skinner recommends the use of flake

naphthalene. In a badly infested house he took one room at a time,

scattering on the floor five pounds of flake naphthalene, and closed it

for twenty-four hours. It proved to be a perfect and effectual remedy

and very inexpensive, as the naphthalene could be swept up and

transferred to other rooms. Dr. Skinner adds, "so far as I am concerned,

the flea question is solved and if I have further trouble I know the

remedy. I intend to keep the dog and cat."

The late Professor Slingerland very effectively used hydrocyanic acid

gas fumigation in exterminating fleas in houses. In one case, where

failure was reported, he found on investigation that the house had

become thoroughly reinfested from pet cats, which had been left

untreated. Fumigation with sulphur is likewise efficient.

The fact that adult fleas are usually to be found on the floor, when not

on their hosts, was ingeniously taken advantage of by Professor S. H.

Gage in ridding an animal room at Cornell University of the pests. He

swathed the legs of a janitor with sticky fly-paper and had him walk

back and forth in the room. Large numbers of the fleas were collected in

this manner.

In some parts of the southern United States hogs are commonly infested

and in turn infest sheds, barns and even houses. Mr. H. E. Vick informs

us that it is a common practice to turn sheep into barn-lots and sheds

in the spring of the year to collect in their wool, the fleas which

abound in these places after the hogs have been turned out.

It is a common belief that adult fleas are attracted to fresh meat and

that advantage of this can be taken in trapping them. Various workers,

notably Mitzman (1910), have shown that there is no basis for such a

belief.

THE TRUE CHIGGERS--The chigoes, or true chiggers, are the most

completely parasitic of any of the fleas. Of the dozen or more known

species, one commonly attacks man. This is _Dermatophilus penetrans_,

more commonly known as _Sarcopsylla penetrans_ or _Pulex penetrans_.

This species occurs in Mexico, the West Indies, Central and South

America. There are no authentic records of its occurrence in the United

States although, as Baker has pointed out, there is no reason why it

should not become established in Florida and Texas. It is usually

believed that Brazil was its original home. Sometime about the middle of

the nineteenth century it was introduced into West Africa and has spread

across that continent.

The males and the immature females of _Dermatophilus penetrans_ (fig.

93) closely resemble those of other fleas. They are very active little

brown insects about 1-1.2 mm. in size, which live in the dust of native

huts and stables, and in dry, sandy soil. In such places they often

occur in enormous numbers and become a veritable plague.

[Illustration: 93. Dermatophilus penetrans. Much enlarged. After

Karsten.]

They attack not only man but various animals. According to Castellani

and Chalmers, "Perhaps the most noted feature is the way in which it

attacks pigs. On the Gold Coast it appeared to be largely kept in

existence by these animals. It is very easily captured in the free state

by taking a little pig with a pale abdomen, and placing it on its back

on the ground on which infected pigs are living. After watching a few

moments, a black speck will appear on the pig's abdomen, and quickly

another and another. These black specks are jiggers which can easily be

transferred to a test tube. On examination they will be found to be

males and females in about equal numbers."

Both the males and females suck blood. That which characterizes this

species as distinguished from other fleas attacking man is that when the

impregnated female attacks she burrows into the skin and there swells

until in a few days she has the size and appearance of a small pea (fig.

94). Where they are abundant, hundreds of the pests may attack a single

individual (fig. 95). Here they lie with the apex of the abdomen

blocking the opening. According to Fulleborn (1908) they do not

penetrate beneath the epidermis. The eggs are not laid in the flesh of

the victim, as is sometimes stated, but are expelled through this

opening. The female then dies, withers and falls away or is expelled by

ulceration. According to Brumpt, she first quits the skin and then,

falling to the ground, deposits her eggs. The subsequent development in

so far as known, is like that of other fleas.

[Illustration: 94. Dermatophilus penetrans, gravid female. After

Moniez.]

[Illustration: 95. Chiggers in the sole of foot of man. Manson's

Tropical Diseases. Permission of Cassell and Co.]

The chigoe usually enters between the toes, the skin about the roots of

the nails, or the soles of the feet, although it may attack other parts

of the body. Mense records the occurrence in folds of the epidermis, as

in the neighborhood of the anus. They give rise to irritation and unless

promptly and aseptically removed there often occurs pus formation and

the development of a more or less serious abscess. Gangrene and even

tetanus may ensue.

Treatment consists in the careful removal of the insect, an operation

more easily accomplished a day or two after its entrance, than at first,

when it is unswollen. The ulcerated point should then be treated with

weak carbolic acid, or tincture of iodine, or dusted thoroughly with an

antiseptic powder.

[Illustration: 96. Echidnophaga gallinacea.]

[Illustration: 97. Echidnophaga gallinacea infesting head of chicken.

After Enderlein.]

Castellani and Chalmers recommend as prophylactic measures, keeping the

house clean and keeping pigs, poultry, and cattle away therefrom. "High

boots should be used, and especial care should be taken not to go to a

ground floor bathroom with bare feet. The feet, especially the toes, and

under the nails, should be carefully examined every morning to see if

any black dots can be discovered, when the jigger should be at once

removed, and in this way suppuration will be prevented. It is

advisable, also, to sprinkle the floors with carbolic lotion, Jeyes'

fluid, or with pyrethrum powder, or with a strong infusion of native

tobacco, as recommended by Law and Castellani."

_Echidnophaga gallinacea_ (fig. 96) is a widely distributed Hectopsyllid

attacking poultry (fig. 97). It occurs in the Southern and Southwestern

United States and has been occasionally reported as attacking man,

especially children. It is less highly specialized than _Dermatophilus

penetrans_, and does not ordinarily cause serious trouble in man.

CHAPTER IV

ACCIDENTAL OR FACULTATIVE PARASITES

In addition to the many species of Arthropods which are normally

parasitic on man and animals, there is a considerable number of those

which may be classed as _accidental_ or _facultative_ parasites.

Accidental or facultative parasites are species which are normally

free-living, but which are able to exist as parasites when accidentally

introduced into the body of man or other animal. A wide range of forms

is included under this grouping.

ACARINA

A considerable number of mites have been reported as accidental or even

normal, endoparasites of man, but the authentic cases are comparatively

few.

In considering such reports it is well to keep in mind von Siebold's

warning that in view of the universal distribution of mites one should

be on his guard. In vessels in which animal and other organic fluids and

moist substances gradually dry out, mites are very abundantly found. If

such vessels are used without very careful preliminary cleaning, for the

reception of evacuations of the sick, or for the reception of parts

removed from the body, such things may be readily contaminated by mites,

which have no other relation whatever to them.

Nevertheless, there is no doubt but that certain mites, normally

free-living, have occurred as accidental parasites of man. Of these the

most commonly met with is _Tyroglyphus siro_, the cheese-mite.

_Tyroglyphus siro_ is a small mite of a whitish color. The male measures

about 500u long by 250u wide, the female slightly larger. They live in

cheese of almost any kind, especially such as is a little decayed. "The

individuals gather together in winter in groups or heaps in the hollows

and chinks of the cheese and there remain motionless. As soon as the

temperature rises a little, they gnaw away at the cheese and reduce it

to a powder. The powder is composed of excrement having the appearance

of little grayish microscopic balls; eggs, old and new, cracked and

empty; larvae, nymphs, and perfect mites, cast skins and fragments of

cheese, to which must be added numerous spores of microscopic

fungi."--Murray.

_Tyroglyphus siro_, and related species, have been found many times in

human feces, under conditions which preclude the explanation that the

contamination occurred outside of the body. They have been supposed to

be the cause of dysentery, or diarrhoea, and it is probable that the

_Acarus dysenteriae_ of Linnaeus, and Latreille, was this species.

However, there is little evidence that the mites cause any noteworthy

symptoms, even when taken into the body in large numbers.

_Histiogaster spermaticus_ (fig. 152) is a Tyroglyphid mite which was

reported by Trouessart (1902) as having been found in a cyst in the

groin, adherent to the testis. When the cyst was punctured, it yielded

about two ounces of opalescent fluid containing spermatozoa and numerous

mites in all stages of development. The evidence indicated that a

fecundated female mite had been introduced into the urethra by means of

an unclean catheter. Though Trouessart reported the case as that of a

Sarcoptid, Banks places the genus _Histiogaster_ with the Tyroglyphidae.

He states that our species feeds on the oyster-shell bark louse,

possibly only after the latter is dead, and that in England a species

feeds within decaying reeds.

_Nephrophages sanguinarius_ is a peculiarly-shaped, angular mite which

was found by Miyake and Scriba (1893) for eight successive days in the

urine of a Japanese suffering from fibrinuria. Males, .117 mm. long by

.079 mm. wide, females .36 mm. by. 12 mm., and eggs were found both in

the spontaneously emitted urine and in that drawn by means of a

catheter. All the mites found were dead. The describers regarded this

mite as a true endoparasite, but it is more probable that it should be

classed as an accidental parasite.

MYRIAPODA

There are on record a number of cases of myriapods occurring as

accidental parasites of man. The subject has been treated in detail by

Blanchard (1898 and 1902), who discussed forty cases. Since then at

least eight additions have been made to the list.

Neveau-Lamaire (1908) lists thirteen species implicated, representing

eight different genera. Of the _Chilognatha_ there are three, _Julus

terrestris_, _J. londinensis_ and _Polydesmus complanatus_. The

remainder are _Chilopoda_, namely, _Lithobius forficatus_, _L.

malenops_, _Geophilus carpophagus_, _G. electricus_, _G. similis_, _G.

cephalicus_, _Scutigera coleoptrata_, _Himantarium gervaisi_,

_Chaetechelyne vesuviana_ and _Stigmatogaster subterraneus_.

The majority of the cases relate to infestation of the nasal fossae, or

the frontal sinus, but intestinal infestation also occurs and there is

one recorded case of the presence of a species in _Julus_ (fig. 13) in

the auditory canal of a child.

In the nose, the myriapods have been known to live for months and

according to some records, even for years. The symptoms caused by their

presence are inflammation, with or without increased flow of mucus,

itching, more or less intense headache, and at times general symptoms

such as vertigo, delirium, convulsions, and the like. These symptoms

disappear suddenly when the parasites are expelled.

In the intestine of man, myriapods give rise to obscure symptoms

suggestive of infestation by parasitic worms. In a case reported by

Verdun and Bruyant (1912), a child twenty months of age had been

affected for fifteen days by digestive disturbances characterized by

loss of appetite, nausea and vomiting. The latter had been particularly

pronounced for three days, when there was discovered in the midst of the

material expelled a living myriapod of the species _Chaetechelyne

vesuviana_. Anthelminthics had been administered without result. In some

of the other cases, the administration of such drugs had resulted in the

expulsion of the parasite through the anus.

One of the extreme cases on record is that reported by Shipley (1914).

Specimens of _Geophilus gorizensis_ (= _G. subterraneus_) "were vomited

and passed by a woman of 68 years of age. Some of the centipedes emerged

through the patient's nose, and it must be mentioned that she was also

suffering from a round worm. One of her doctors was of the opinion that

the centipedes were certainly breeding inside the lady's intestines, and

as many as seven or eight, sometimes more, were daily leaving the

alimentary canal."

"According to her attendant's statements those centipedes had left the

body in some hundreds during a period of twelve or eighteen months.

Their presence produced vomiting and some haematemesis, and treatment

with thymol, male-fern and turpentine had no effect in removing the

creatures."

The clinical details, as supplied by Dr. Theodore Thompson were as

follows:

"Examined by me July, 1912, her tongue was dry and glazed. There was

bleeding taking place from the nose and I saw a living centipede she had

just extracted from her nostril. Her heart, lungs and abdomen appeared

normal. She was not very wasted, and did not think she had lost much

flesh, nor was there any marked degree of anemia."

Shipley gives the following reasons for believing it impossible that

these centipedes could have multiplied in the patient's intestine. "The

breeding habits of the genus _Geophilus_ are peculiar, and ill adapted

for reproducing in such a habitat. The male builds a small web or nest,

in which he places his sperm, and the female fertilizes herself from

this nest or web, and when the eggs are fertilized they are again laid

in a nest or web in which they incubate and in two or three weeks hatch

out. The young _Geophilus_ differ but very little from the adult, except

in size. It is just possible, but improbable, that a clutch of eggs had

been swallowed by the host when eating some vegetables or fruit, but

against this is the fact that the _Geophilus_ does not lay its eggs upon

vegetables or fruit, but upon dry wood or earth. The egg-shell is very

tough and if the eggs had been swallowed the egg-shells could certainly

have been detected if the dejecta were examined. The specimens of the

centipede showed very little signs of being digested, and it is almost

impossible to reconcile the story of the patient with what one knows of

the habits of the centipedes."

In none of the observed cases have there been any clear indications as

to the manner of infestation. It is possible that the myriapods have

been taken up in uncooked fruit or vegetables.

LEPIDOPTEROUS LARVAE

SCHOLECIASIS--Hope (1837) brought together six records of infestation of

man by lepidopterous larvae and proposed to apply the name scholeciasis

to this type of parasitism. The clearest case was that of a young boy

who had repeatedly eaten raw cabbage and who vomited larvae of the

cabbage butterfly, _Pieris brassicae_. Such cases are extremely rare, and

there are few reliable data relative to the subject. In this connection

it may be noted that Spuler (1906) has described a moth whose larvae live

as ectoparasites of the sloth.

COLEOPTERA

CANTHARIASIS--By this term Hope designated instances of accidental

parasitism by the larvae or adults of beetles. Reports of such cases

are usually scouted by parasitologists but there seems no good basis for

wholly rejecting them. Cobbold refers to a half dozen cases of

accidental parasitism by the larvae of _Blaps mortisaga_. In one of

these cases upwards of 1200 larvae and several perfect insects were

said to have been passed _per annum_. French (1905) reports the case of

a man who for a considerable period voided adult living beetles of the

species _Nitidula bipustulata_. Most of the other cases on record relate

to the larvae of _Dermestidae_ (larder beetles _et al._) or

_Tenebrionidae_ (meal infesting species). Infestation probably occurs

through eating raw or imperfectly cooked foods containing eggs or minute

larvae of these insects.

[Illustration: 98. Larva of Piophila casei. Caudal aspect of larva.

Posterior stigmata.]

Brumpt cites a curious case of accidental parasitism by a coleopterous

larva belonging to the genus _Necrobia_. This larva was extracted from a

small tumor, several millimeters long, on the surface of the conjunctiva

of the eye. The larvae of this genus ordinarily live in decomposing flesh

and cadavers.

DIPTEROUS LARVAE

[Illustration: 99. Piophila casei. After Graham-Smith.]

MYASIS--By this term (spelled also myiasis, and myiosis), is meant

parasitism by dipterous larvae. Such parasitism may be normal, as in the

cases already described under the heading parasitic Diptera, or it may

be facultative, due to free-living larvae being accidentally introduced

into wounds or the body-cavities of man. Of this latter type, there is a

multitude of cases on record, relating to comparatively few species. The

literature of the subject, like that relating to facultative parasitism

in general, is unsatisfactory, for most of the determinations of species

have been very loose. Indeed, so little has been known regarding the

characteristics of the larvae concerned that in many instances they could

not be exactly determined. Fortunately, several workers have undertaken

comparative studies along this line. The most comprehensive publication

is that of Banks (1912), entitled "The structure of certain dipterous

larvae, with particular reference to those in human food."

Without attempting an exhaustive list, we shall discuss here the more

important species of Diptera whose larvae are known to cause myasis,

either external or internal. The following key will serve to determine

those most likely to be encountered. The writers would be glad to

examine specimens not readily identifiable, if accompanied by exact data

relative to occurrence.

_a._ Body more or less flattened, depressed; broadest in the middle,

each segment with dorsal, lateral, and ventral fleshy processes, of

which the laterals, at least, are more or less spiniferous (fig.

101). _Fannia_ (= _Homalomyia_).

In _F. canicularis_ the dorsal processes are nearly as long as the

laterals; in _F. scalaris_ the dorsal processes are short spinose

tubercles.

_aa._ Body cylindrical, or slender conical tapering toward the head;

without fleshy lateral processes (fig. 105).

_b._ With the posterior stigmata at the end of shorter or longer

tubercles, or if not placed upon tubercles, then not in pit; usually

without a "marginal button" and without a chitinous ring surrounding

the three slits; the slits narrowly or broadly oval, not bent (fig.

171 i). _Acalyptrate muscidae_ and some species of

_Anthomyiidae_. To this group belong the cheese skipper (_Piophila

casei_, figs. 98, 99), the pomace-fly (_Drosophila ampelophila_),

the apple maggot (_Rhagoletis pomonella_), the cherry fruit fly

(_Rhagoletis cingulata_), the small dung fly (_Sepsis violacea_,

fig. 170), the beet leaf-miner (_Pegomyia vicina_, fig. 171 i), the

cabbage, bean and onion maggots (_Phorbia_ spp.) et. al.

_bb._ Posterior stigmata of various forms, if the slits are narrowly

oval (fig. 171) then they are surrounded by a chitin ring which may

be open ventro-mesally.

_c._ Integument leathery and usually strongly spinulose; larvae

hypodermatic or endoparasitic. Bot flies (fig. 171, f, g,

k).--_Oestridae_

_cc._ Integument not leathery and (except in _Protocalliphora_) spinulae

restricted to transverse patches near the incisures of the segments.

_d._ The stigmal plates in a pit; the lip-like margin of the pit with a

number of fleshy tubercles; chitin ring of the stigma not complete;

open ventro-mesally, button absent (fig. 171 e). Flesh

flies.--_Sarcophaga_

_dd._ Stigmata not in a pit.

_e._ The chitin ring open ventra-mesally; button absent (fig. 171 c).

Screw-worm fly. _Chrysomyia_

_ee._ The chitin ring closed.

_f._ Slits of the posterior stigmata straight; marginal "button" present

(fig. 171 b); two distinct mouth hooks, fleshy tubercles around the

anal area. _Phormia_ (fig. 171 f), _Lucilia_ and _Calliphora_ (fig.

172, a, b), _Protocalliphora_ (fig. 171, j), _Cynomyia_ (fig. 171,

a). Blow flies, bluebottle flies. _Calliphorinae_

_ff._ Slits of the posterior stigmata sinuous or bent. Subfamily

Muscinae.

_g._ Slits of the posterior stigmata bent; usually two mouth hooks.

_Muscina stabulans_ (fig. 171, l), _Muscina similis_, _Myiospila

meditabunda_ (fig. 172, i), and some of the higher _Anthomyiidae_.

_gg._ Slits of the posterior stigmata sinuous; mouth hooks usually

consolidated into one. The house-fly (_Musca domestica_ fig. 171,

d), the stable fly (_Stomoxys calcitrans_), the horn fly (_Lyperosia

irritans_), _Pyrellia_, _Pseudopyrellia_, _Morellia_, _Mesembrina_.

_Polietes_, et. al. (fig. 172 in part).

_Eristalis_--The larvae of _Eristalis_ are the so-called rat-tailed

maggots, which develop in foul water. In a few instances these larvae

have been known to pass through the human alimentary canal uninjured.

Hall and Muir (1913) report the case of a boy five years of age, who had

been ailing for ten weeks and who was under treatment for indigestion

and chronic constipation. For some time he had vomited everything he

ate. On administration of a vermifuge he voided one of the rat-tailed

maggots of _Eristalis_. He admitted having drunk water from a ditch full

of all manner of rotting matter. It was doubtless through this that he

became infested. It is worth noting that the above described symptoms

may have been due to other organisms or substances in the filthy water.

_Piophila casei_, the cheese-fly (fig. 99), deposits its eggs not only

in old cheeses, but on ham, bacon, and other fats. The larvae (fig. 98)

are the well-known cheese skippers, which sometimes occur in great

abundance on certain kinds of cheese. Indeed, some people have a

comfortable theory that such infested cheese is especially good. Such

being the case, it is small wonder that this species has been repeatedly

reported as causing intestinal myasis. Thebault (1901) describes the

case of a girl who, shortly after consuming a large piece of badly

infested cheese, became ill and experienced severe pains in the region

of the navel. Later these extended through the entire alimentary canal,

the excrement was mixed with blood and she suffered from vertigo and

severe headaches. During the four following days the girl felt no

change, although the excretion of the blood gradually diminished and

stopped. On the fourth day she voided two half-digested larvae and,

later, seven or eight, of which two were alive and moving.

That these symptoms may be directly attributed to the larvae, or

"skippers," has been abundantly shown by experimental evidence.

Portschinsky cites the case of a dog fed on cheese containing the larvae.

The animal suffered much pain and its excrement contained blood. On

_post mortem_ it was found that the small intestine throughout almost

its entire length was marked by bloody bruises. The papillae on these

places were destroyed, although the walls were not entirely perforated.

In the appendix were found two or three dead larvae. Alessandri (1910)

has likewise shown that the larvae cause intestinal lesions.

According to Graham-Smith, Austen (1912) has recorded a case of myasis

of the nose, attended with a profuse watery discharge of several weeks

duration and pain, due to the larvae of _Piophila casei_.

ANTHYOMYIIDAE--The characteristic larvae of two species of _Fannia_ (=

_Homalomyia_ or _Anthomyia_, in part) (fig. 101) are the most commonly

reported of dipterous larvae causing intestinal myasis. Hewitt (1912) has

presented a valuable study of the bionomics and of the larvae of these

flies, a type of what is needed for all the species concerned in myasis.

We have seen two cases of their having been passed in stools, without

having caused any special symptoms. In other instances their presence in

the alimentary canal has given rise to symptoms vaguely described as

those of tapeworm infestation, or helminthiasis. More specifically, they

have been described as causing vertigo, severe headache, nausea and

vomiting, severe abdominal pains, and in some instances, bloody

diarrhoea.

[Illustration: 100. Fannia canicularis (x4). After Graham-Smith.]

One of the most striking cases is that reported by Blankmeyer (1914), of

a woman whose illness began fourteen years previously with nausea and

vomiting. After several months of illness she began passing larvae and

was compelled to resort to enemas. Three years previous to the report,

she noticed frequent shooting pains in the rectal region and at times

abdominal tenderness was marked. There was much mucus in the stools and

she "experienced the sensation of larvae crawling in the intestine."

Occipital headaches were marked, with remissions, and constipation

became chronic. The appetite was variable, there was a bad taste in the

mouth, tongue furred and ridged, and red at the edges. Her complexion

was sallow, and general nervousness was marked. As treatment, there were

given doses of magnesium sulphate before breakfast and at 4 P. M., with

five grain doses of salol four times a day. The customary parasiticides

yielded no marked benefit. At the time of the report the patient passed

from four to fifty larvae per day, and was showing some signs of

improvement. The nausea had disappeared, her nervousness was less

evident, and there was a slight gain in weight.

The case was complicated by various other disorders, but the symptoms

given above seem to be in large part attributable to the myasis. There

is nothing in the case to justify the assumption that larvae were

continuously present, for years. It seems more reasonable to suppose

that something in the habits of the patient favored repeated

infestation. Nevertheless, a study of the various cases of intestinal

myasis caused by these and other species of dipterous larvae seems to

indicate that the normal life cycle may be considerably prolonged under

the unusual conditions.

The best authenticated cases of myasis of the urinary passage have been

due to larvae of _Fannia_. Chevril (1909) collected and described twenty

cases, of which seven seemed beyond doubt. One of these was that of a

woman of fifty-five who suffered from albuminuria, and urinated with

much difficulty, and finally passed thirty to forty larvae of _Fannia

canicularis_.

It is probable that infestation usually occurs through eating partially

decayed fruit or vegetables on which the flies have deposited their

eggs. Wellman points out that the flies may deposit their eggs in or

about the anus of persons using outside privies and Hewitt believes that

this latter method of infection is probably the common one in the case

of infants belonging to careless mothers. "Such infants are sometimes

left about in an exposed and not very clean condition, in consequence of

which flies are readily attracted to them and deposit their eggs."

[Illustration: 101. Larva of Fannia scalaris.]

MUSCINAE--The larvae of the common house-fly, _Musca domestica_, are

occasionally recorded as having been passed with the feces or vomit of

man. While such cases may occur, it is probable that in most instances

similar appearing larvae of other insects have been mistakenly

identified.

_Muscina stabulans_ is regarded by Portschinsky (1913) as responsible

for many of the cases of intestinal myasis attributed to other species.

He records the case of a peasant who suffered from pains in the lower

part of the breast and intestines, and whose stools were mixed with

blood. From November until March he had felt particularly ill, being

troubled with nausea and vomiting in addition to the pain in his

intestines. In March, his physician prescribed injections of a

concentrated solution of tannin, which resulted in the expulsion of

fifty living larvae of _Muscina stabulans_. Thereafter the patient felt

much better, although he suffered from intestinal catarrh in a less

severe form.

[Illustration: 102 Muscina stabulans (x4). After Graham-Smith.]

CALLIPHORINAE--Closely related to the Sarcophagidae are the

_Calliphorinae_, to which group belong many of the so-called "blue

bottle" flies. Their larvae feed upon dead animals, and upon fresh and

cooked meat. Those of _Protocalliphora_, already mentioned, are

ectoparasitic on living nestling birds. Larva of _Lucilia_, we have

taken from tumors on living turtles. To this sub-family belongs also

_Auchmeromyia luteola_, the Congo floor maggot. Some of these, and at

least the last mentioned, are confirmed, rather than faculative

parasites. Various species of Calliphorinae are occasionally met with as

facultative parasites of man.

[Illustration: 103. Lucilia caesar, (x3). After Howard.]

_Chrysomyia macellaria_, the screw worm fly (fig. 107), is the fly which

is responsible for the most serious cases of human myasis in the United

States. It is widely distributed in the United States but is especially

abundant in the south. While the larvae breed in decaying matter in

general, they so commonly breed in the living flesh of animals that they

merit rank as true parasites. The females are attracted to open wounds

of all kinds on cattle and other animals and quickly deposit large

numbers of eggs. Animals which have been recently castrated, dehorned,

or branded, injured by barbed wire, or even by the attacks of ticks are

promptly attacked in the regions where the fly abounds. Even the navel

of young calves or discharges from the vulva of cows may attract the

insect.

[Illustration: 104. Calliphora erythrocephala, (x6). After

Graham-Smith.]

Not infrequently the fly attacks man, being attracted by an offensive

breath, a chronic catarrh, or a purulent discharge from the ears. Most

common are the cases where the eggs are deposited in the nostrils. The

larvae, which are hatched in a day or two, are provided with strong

spines and proceed to bore into the tissues of the nose, even down into

or through the bone, into the frontal sinus, the pharynx, larynx, and

neighboring parts.

Osborn (1896) quotes a number of detailed accounts of the attacks of the

_Chrysomyia_ on man. A vivid picture of the symptomology of rhinal

myasis caused by the larvae of this fly is given by Castellani and

Chalmers: "Some couple of days after a person suffering from a chronic

catarrh, foul breath, or ozaena, has slept in the open or has been

attacked by a fly when riding or driving,--_i.e._, when the hands are

engaged--signs of severe catarrh appear, accompanied with inordinate

sneezing and severe pain over the root of the nose or the frontal bone.

Quickly the nose becomes swollen, and later the face also may swell,

while examination of the nose may show the presence of the larvae. Left

untreated, the patient rapidly becomes worse, and pus and blood are

discharged from the nose, from which an offensive odor issues. Cough

appears as well as fever, and often some delirium. If the patient lives

long enough, the septum of the nose may fall in, the soft and hard

palates may be pierced, the wall of the pharynx may be destroyed. By

this time, however, the course of the disease will have become quite

evident by the larvae dropping out of the nose, and if the patient

continues to live all the larvae may come away naturally."

For treatment of rhinal myasis these writers recommend douching the nose

with chloroform water or a solution of chloroform in sweet milk (10-20

per cent), followed by douches of mild antiseptics. Surgical treatment

may be necessary.

[Illustration: 105. Larva of a flesh fly (Sarcophaga). Caudal aspect.

Anterior stigmata. Pharyngeal skeleton.]

SARCOPHAGIDAE--The larvae (fig. 105) of flies of this family usually

feed upon meats, but have been found in cheese, oleomargerine, pickled

herring, dead and living insects, cow dung and human feces. Certain

species are parasitic in insects. Higgins (1890) reported an instance of

"hundreds" of larvae of _Sarcophaga_ being vomited by a child eighteen

months of age. There was no doubt as to their origin for they were

voided while the physician was in the room. There are many other reports

of their occurrence in the alimentary canal. We have recorded elsewhere

(Riley, 1906) a case in which some ten or twelve larvae of

_Sarcophaga_ were found feeding on the diseased tissues of a malignant

tumor. The tumor, a melanotic sarcoma, was about the size of a small

walnut, and located in the small of the back of an elderly lady.

Although they had irritated and caused a slight haemorrhage, neither the

patient nor others of the family knew of their presence. Any discomfort

which they had caused had been attributed to the sarcomatous growth. The

infestation occurred in mid-summer. It is probable that the adult was

attracted by the odor of the discharges and deposited the living maggots

upon the diseased tissues.

[Illustration: 106. A flesh fly (Sarcophaga), (x4). After Graham-Smith.]

According to Kuchenmeister, _Sarcophaga carnaria_ (fig. 106), attracted

by the odor, deposits its eggs and larvae in the vagina of girls and

women when they lie naked in hot summer days upon dirty clothes, or when

they have a discharge from the vagina. In malignant inflammations of the

eyes the larvae even nestle under the eyelids and in Egypt, for example,

produce a very serious addition to the effects of small-pox upon the

cornea, as according to Pruner, in such cases perforation of the cornea

usually takes place.

[Illustration: 107. Chrysomyia macellaria, (x3).]

_Wohlfartia magnifica_ is another Sarcophagid which commonly infests man

in the regions where it is abundant. It is found in all Europe but is

especially common in Russia, where Portschinsky has devoted much

attention to its ravages. It deposits living larvae in wounds, the nasal

fossae, the ears and the eyes, causing injuries even more revolting than

those described for _Chrysomyia_.

CHAPTER V

ARTHROPODS AS SIMPLE CARRIERS OF DISEASE

The fact that certain arthropods are poisonous, or may affect the health

of man as direct parasites has always received attention in the medical

literature. We come now to the more modern aspect of our subject,--the

consideration of insects and other arthropods as transmitters and

disseminators of disease.

The simplest way in which arthropods may function in this capacity is as

_simple carriers_ of pathogenic organisms. It is conceivable that any

insect which has access to, and comes in contact with such organisms and

then passes to the food, or drink, or to the body of man, may in a

wholly accidental and incidental manner convey infection. That this

occurs is abundantly proved by the work of recent years. We shall

consider as typical the case against the house-fly, which has attracted

so much attention, both popular and scientific. The excellent general

treatises of Hewitt (1910), Howard (1911), and Graham-Smith (1913), and

the flood of bulletins and popular literature render it unnecessary to

consider the topic in any great detail.

THE HOUSE-FLY AS A CARRIER OF DISEASE

Up to the past decade the house-fly has usually been regarded as a mere

pest. Repeatedly, however, it had been suggested that it might

disseminate disease. We have seen that as far back as the sixteenth

century, Mercurialis suggested that it was the agent in the spread of

bubonic plague, and in 1658, Kircher reiterated this view. In 1871,

Leidy expressed the opinion that flies were probably a means of

communicating contagious diseases to a greater degree than was generally

suspected. From what he had observed regarding gangrene in hospitals, he

thought flies should be carefully excluded from wounds. In the same

year, the editor of the _London Lancet_, referring to the belief that

they play a useful role in purifying the air said, "Far from looking

upon them as dipterous angels dancing attendance on Hygeia, regard them

rather in the light of winged sponges spreading hither and thither to

carry out the foul behests of Contagion."

These suggestions attracted little attention from medical men, for it is

only within very recent years that the charges have been supported by

direct evidence. Before considering this evidence, it is necessary that

we define what is meant by "house-fly" and that we then consider the

life-history of the insect.

There are many flies which are occasionally to be found in houses, but

according to various counts, from 95 per cent to 99 per cent of these in

warm weather in the Eastern United States belong to the one species

_Musca domestica_ (fig. 108). This is the dominant house-fly the world

over and is the one which merits the name. It has been well

characterized by Schiner (1864), whose description has been freely

translated by Hewitt, as follows:

"Frons of male occupying a fourth part of the breadth of the head.

Frontal stripe of female narrow in front, so broad behind that it

entirely fills up the width of the frons. The dorsal region of the

thorax dusty grey in color with four equally broad longitudinal stripes.

Scutellum gray with black sides. The light regions of the abdomen

yellowish, transparent, the darkest parts at least at the base of the

ventral side yellow. The last segment and a dorsal line blackish brown.

Seen from behind and against the light, the whole abdomen shimmering

yellow, and only on each side of the dorsal line on each segment a dull

transverse band. The lower part of the face silky yellow, shot with

blackish brown. Median stripe velvety black. Antennae brown. Palpi black.

Legs blackish brown. Wings tinged with pale gray with yellowish base.

The female has a broad velvety back, often reddishly shimmering frontal

stripe, which is not broader at the anterior end than at the bases of

the antennae, but become so very much broader above that the light

dustiness of the sides is entirely obliterated. The abdomen gradually

becoming darker. The shimmering areas on the separate segments generally

brownish. All the other parts are the same as in the male."

The other species of flies found in houses in the Eastern United States

which are frequently mistaken for the house or typhoid fly may readily

be distinguished by the characters of the following key:

_a._ Apical cell (R_5) of the wide wing open, i.e., the bounding veins

parallel or divergent (fig. 100). Their larvae are flattened, the

intermediate body segments each fringed with fleshy, more or less

spinose, processes. _Fannia_

b. Male with the sides of the second and third abdominal segments

translucent yellowish. The larva with three pairs of nearly equal

spiniferous appendages on each segment, arranged in a

longitudinal series and in addition two pairs of series of smaller

processes (fig. 100) _F. canicularis_