LITTLE BLUE BOOK NO. 860
Edited by E. Haldeman-Julius
Our Insect Enemies
Vance Randolph
Drawings by Peter Quinn
HALDEMAN-JULIUS COMPANY
GIRARD, KANSAS
Copyrighted, 1925,
Haldeman-Julius Company
CONTENTS
Page
Houseflies and Their Kindred 4
Mosquitoes and Disease 28
Life Among the Bedbugs 43
Lice, Crabs and Cooties 47
Our Friend the Cockroach 54
Chiggers, Ticks and Fleas 57
PRINTED IN THE UNITED STATES OF AMERICA
LIST OF ILLUSTRATIONS
Page
Fig. I. The Metamorphosis of the Housefly (_Musca domestica_). 12
Fig. II. Malaria and its Carrier. 33
Fig. III. Three kinds of Lice. 51
Fig. IV. Some Common Cockroaches. 58
Fig. V. Chiggers and Ticks. 61
OUR INSECT ENEMIES
HOUSEFLIES AND THEIR KINDRED
The common housefly (_Musca domestica_) is perhaps more thoroughly
domesticated than any other insect; it lives and flourishes wherever
man has established his settlements, and does not thrive elsewhere. It
is mentioned by many of the ancient writers, and has evidently been
associated with man from the remotest antiquity, doubtless adapting
itself gradually to his changing modes of life. It still breeds in the
refuse which accumulates about his buildings, and still invades his
home to partake of his food. When one considers the number of flies
which get into modern dwellings despite glass and wire and modern
insecticides, it is difficult to understand how our sturdy fathers
managed to survive the summers in mediaeval Europe. Picture Thomas
Aquinas battling with swarms of flies for his food! The housefly’s
favorite breeding place has always been in horse manure, and man has
until recent years had great quantities of this nutritious substance
about him; with the coming of the automobile this condition has been
changed somewhat, but even the cleanest of American cities still
affords sufficient decaying matter to assure a bountiful crop of flies.
At some future day perhaps we shall have cities so spotless that there
will be nowhere a speck of garbage large enough to nourish a maggot,
but that day is still to come, and it doth not yet appear what we shall
be.
Meanwhile, as Herrick says, the housefly is with us always. “They are
present from early spring to late fall, even remaining far into the
winter. They are troublesome in kitchens and dining rooms because of
their abundance, their proneness to get into food, and their generally
filthy habits. Until recent years the housefly has been generally
regarded as somewhat of a scavenger and has been considered of value
to humanity because of its aid in the removal of wastes that are a
menace to human welfare. The eggs of the housefly are often deposited
on decaying vegetable matter that is allowed to accumulate in the
vicinity of human habitations and the maggots that hatch from the eggs
live on this decaying matter and aid in destroying it. Thus it must be
conceded, perhaps, that houseflies do assist somewhat in the removal of
foul and dangerous waste matters and, to this extent, are of benefit.
On the other hand, it has been conclusively shown that this modicum
of benefit is greatly overbalanced by their role in disseminating
dangerous diseases. It has been shown that houseflies carry the germs
of cholera, typhoid fever, cholera infantum, and tropical dysentery on
their feet, legs, bodies and in their digestive tracts. There can be no
doubt of the responsibility of the housefly for much sickness and many
deaths.”
Although the adult housefly is equally fond of fresh and putrid matter,
flitting from filth to food and back again, the eggs are always laid in
decaying substances, preferably horse manure. In the absence of this
delicacy the eggs may be deposited in human excrement, or even cow
manure if it is not too dry. A single female fly often deposits one
hundred and fifty eggs at a single sitting, and lays as many as six or
seven hundred in the course of a season.
The egg is white and shaped like a grain of wheat; it measures
about one-twentieth of an inch in length, and hatches in from ten
to twenty-four hours, the period of incubation varying with the
temperature. The second or larval stage is represented by a wormlike
creature called a maggot, which crawls about and devours great
quantities of nourishing manure. When the maggot is about five or six
days old it has attained a length of nearly three-eighths of an inch,
and transforms into the pupa; it is no longer active, ceases to take
food, and the outer skin turns into a hard, brown, dry case called a
puparium. After five or six days of rest the puparium is burst open and
the adult fly crawls out.
The newly emerged flies mate within two or three days, and the young
females are soon laying their first batch of eggs. Thus the whole
development may occur in about fourteen days, and Herrick thinks that
in Washington, D. C., it may be complete in ten days or less, according
to the temperature, with ten or twelve generations in a summer. “One
can hardly realize,” says Herrick, “the enormous numbers that such
rapid development is capable of producing. Inside of two months, one
female fly can give rise to many millions of progeny. For the purpose
of illustration, we will assume that a female fly lays 100 eggs. If
these hatch and all the larvae come to maturity, about one-half will
probably be males and the other half females. Then at the end of the
first generation there will be fifty egg-laying females. At this rate,
at the end of the eighth generation there would be produced about
1,875,000,000,000 adults. Of course, in nature, a very large part of
these would die before reaching maturity, so that actually one female
would probably never produce such an enormous number of individuals.
However, even under normal conditions tremendous numbers are produced.”
The adult housefly is unhappily too familiar to require a lengthy
description. The total length is about one-fourth of an inch, there are
two membranous wings and six hairy legs, while the thorax is gray with
four dark longitudinal stripes above. Besides the hairs and bristles on
the body and legs, which entangle great numbers of germs, the sticky
_pulvilli_ of the feet gather bacteria as if they had been especially
developed for that purpose. Thus every housefly scatters bacteria
broadcast wherever he goes; one has only to allow a fly to walk
across a plate of sterile gelatin to see large colonies of bacteria
produced in every foot-print. Esten and Mason’s examination of some 400
specimens showed that the number of bacteria carried ranged from 550 to
6,600,000 per fly, with an average of nearly a million and a quarter.
The general impression is that the housefly does not travel any great
distance from its birth-place, but there is considerable doubt
about this matter. Hewitt has taken them flying at least eighty feet
above the ground, and it is obvious that small insects which rise
so high may be carried long distances by the wind. Copeman, Howlett
and Merriman have attacked the problem by marking large numbers of
specimens, releasing them, and then watching for them in traps set at
various distances; they recovered several which had travelled more than
three-fourths of a mile. Dr. Hodge found plenty of houseflies on the
cribs of the Cleveland waterworks, which are located six miles out in
Lake Erie, and which offer no breeding places for flies. He naturally
concluded that they were blown six miles by the wind.
It has been pretty well established that adult flies do not retain
and disseminate disease germs which they swallowed as maggots in the
manure, but only those which they acquire in the adult state. It has
been definitely proved, however, that the bacilli of typhoid fever are
carried on the bodies and legs of houseflies, and also that the bacilli
are often swallowed and survive the passage through the body, as living
bacilli have frequently been demonstrated in flyspecks. The most
important practical consideration is, of course, the actual frequency
with which houseflies do transfer pathogenic organisms from filth to
food intended for human consumption, thus spreading disease, and this
is in its very nature a difficult matter to investigate.
Typhoid fever is a disease affecting the intestines, and the bacilli
which cause it frequently remain in the body for long periods after
the patient has apparently recovered. The germs are passed out in the
urine and fecal matter. As Herrick puts it: “If the excreta or urine
containing these bacilli are deposited where they are accessible to
flies, for instance in open privies, the chances are high that the
bacilli will be carried on the bodies of these insects back to the
kitchens and dining rooms and be deposited on our food. During the
Spanish-American War, flies were traced by their whitened feet from
the lime-sprinkled, open latrines or privies to the dining tables of
the soldiers in camp. It makes one shudder to think of the thousands
of open closets in the small towns of the United States to which flies
have access and in which they breed and from which they may come direct
to our kitchens and dining rooms.”
Excluding the greater variability of the water supply, the fact that
typhoid is so much more prevalent in country districts than in the
city may be due almost entirely to the abundance of flies, since
other opportunities for infection are no greater than in the city.
Certain South American cities have very good water, but typhoid rages
nevertheless, because the natives expose their excreta within a few
feet of the street markets, and myriads of flies carry the bacilli
from the dunghill to the food. “In our own country,” says Brues, “the
seasonal incidence of typhoid fever corresponds to some extent with fly
prevalence, and still more significant is its greater summer prevalence
in regions where systems for sewage disposal are not generally
installed.... The greater uniformity throughout the year in New York,
where the opportunities for fly-borne infection are curtailed, is very
marked. Another way in which the housefly can aid in the spread of
typhoid is through infecting milk on dairy farms where carriers are
present and offer the flies a chance to become infected.”
The vessels in an ordinary country dairy are nearly always more or less
accessible to flies, and warm milk is an excellent medium in which to
cultivate bacteria. When a fly which has been feeding on the excreta
of a typhoid patient falls into a can of milk, there is a very good
chance that the disease may be spread all along the milkman’s route.
Dr. Taylor, of the Colorado State Board of Health, reports a case of
this sort: “In the city of Denver we had a very sad as well as a plain
demonstration of the transmission of typhoid fever by flies and milk.
Early in August of this year the wife of a dairyman was taken with
typhoid fever, remaining at home about three weeks before her removal
to the hospital, August 28. During the first two weeks of September we
received reports of numerous cases of typhoid fever in the northern
portion of Denver, and upon investigation found that all these cases
had been securing their milk from this dairy.
“An inspection of the dairy was then made, and in addition to learning
of the illness of the dairyman’s wife, we also found the dairyman
himself suffering with a mild case of typhoid, but still up and
delivering milk. The water supply of the dairy was fairly good.
However, we found that the stools of both the wife and husband
had been deposited in an open privy vault located only thirty-five
feet from the milk house, which was unscreened and open to flies.
The gelatin cultures exposed for thirty minutes in the rear of the
privy vault and in the milk house among the milk cans gave numerous
colonies of typhoid bacilli, as well as colon bacilli and the ordinary
germ-life. The source of infection in the dairyman’s wife’s case is
unknown, but I am positive that in all the cases which occurred on this
milk route the infection was due to bacilli carried from this vault by
flies and deposited upon the milk cans, separator and utensils in the
milk house, thereby contaminating the milk. The dairyman supplied milk
to 143 customers. Fifty-five cases of typhoid fever occurred and three
deaths resulted therefrom.”
As long ago as 1873 Dr. Nichols noted that the number of cholera cases
on his ship seemed to vary directly with the abundance of flies. Later
experiments demonstrated the presence of the cholera bacillus upon the
bodies and in the excreta of flies fed upon cholera-infected material,
and it has been shown that flies sometimes transfer the cholera bacilli
from human excreta to milk. Dr. Tsuzuki, of the Japanese Army Medical
Service, found the germs of cholera upon flies taken in cholera-ridden
houses, and demonstrated that flies carry the organisms from place
to place. Macrae, commenting on an outbreak of cholera in a jail in
India, remarked that the place was infested with “a plague of flies ...
which were present in swarms when the disease broke out, and it was
an observation of daily experience to see them settling on cholera
stools whenever possible.” Dr. Macrae goes on to say that the flies
undoubtedly carried the cholera germs to the prisoners’ food, and adds:
“The practical lesson is, that flies should be looked upon in the light
of poisonous agencies of the worst kind during cholera epidemics, and
it is clear that if they find access to poison they will carry and
distribute it, and every possible means should be taken to prevent
their getting into contact with either food or drink of any kind, and
to those having to deal with large bodies of men it is a lesson more
easily learnt than put into practice.”
Because of the flies’ liking for expectorated saliva, it has long been
suspected that tuberculosis may be carried about by these insects.
Several investigators have carried out experiments in which flies have
been fed upon the sputa of consumptives, and the tuberculosis bacilli
have been found in their intestines and fly specks. Frederick T. Lord,
after a long series of laboratory investigations, concluded that: “(1)
Flies may ingest tubercular sputum and excrete tubercle bacilli, the
virulence of which may last for at least fifteen days. (2) The danger
of human infection from tubercular fly specks is by the ingestion
of the specks on food. Spontaneous liberation of tubercle bacilli
from fly specks is unlikely. If mechanically disturbed, infection
of the surrounding air may occur.” Dr. Lord goes on to suggest that
“tubercular material (sputum, pus from discharging sinuses, fecal
matter from patients with intestinal tuberculosis, etc.) should be
carefully protected from flies, lest they act as disseminators of
the tubercle bacilli. During the fly season greater attention should
be paid to the screening of rooms and hospital wards containing
patients with tuberculosis and laboratories where tubercular material
is examined. As these precautions would not eliminate fly infection by
patients at large, foodstuffs should be protected from flies which may
already have ingested tubercular material.”
[Illustration:
Fig. I. The Metamorphosis of the Housefly (_Musca domestica_). A,
eggs, considerably enlarged; B, young maggot; C, puparium; D, pupa;
E, adult.
]
Numerous British army surgeons long ago hazarded the guess that flies
carry dysentery, but the first clear case is that of an epidemic which
occurred in the Worcester State Hospital in 1910. Houseflies were
especially abundant at the time, and Dr. Orton, after a painstaking
experimental study of the affair, concluded that flies were entirely
responsible for the epidemic.
There is now a fairly general agreement that flies spread the organisms
which cause the infantile diarrhea known as summer complaint, which
kills more infants than any other single cause except lack of
sufficient and proper food. Fraser, Nash and others have noted that the
more flies the more cases of summer complaint, and Sandilands explains
the immunity of the children of the rich by the smaller number of flies
in their houses. It is certainly true that the mortality of bottle-fed
infants is very much higher than of breast-fed babies, but whether
Jackson is justified in attributing this mainly to the infection of
cow’s milk by flies is a question.
Lucian Howe has long contended that purulent ophthalmia--the sore-eye so
common up and down the valley of the Nile--is distributed mainly by
the housefly. The disease is always most prevalent where the flies are
most abundant, and in flyless desert regions there is practically no
ophthalmia. The natives are singularly dirty and indolent, and flies are
often seen to settle undisturbed about a pair of badly infected eyes.
Dr. Howe has captured a number of these flies, and found that their
feet were covered with the same bacilli found in the secretion of the
inflamed conjunctiva.
Braun, Demetriades and others report that gonorrheal and other eye
infections are often carried by houseflies. Welander, in 1896,
according to Howard, “observed an interesting case where an old
bed-ridden woman in a hospital became infected. It seems that her bed
was along side that of another patient who had blennorrhea, but that
a screen which did not reach the ceiling separated the beds. Thus all
means of infection except through the agency of flies was apparently
absent. The investigator found that flies bore living gonococci upon
their feet three hours after they had been soiled with secretion, since
they infected sterilized plates with which they came in contact.”
Nuttall and Jepson, after reviewing the entire literature of the
subject, think that “the evidence regarding the spread of Egyptian
ophthalmia by flies appears to be conclusive, and the possibility of
gonorrheal secretions being conveyed by flies cannot be denied.”
Bubonic plague is now definitely known to be spread by fleas which are
parasitic on rats, but many observers still cling to the view that the
housefly also acts as a distributor. It is certainly true that flies
are killed by feeding upon the bodies of persons who die of the plague,
and Yersin, at Hong Kong in 1894, showed that these dead flies contain
active plague bacilli. Whether the fly plays any serious part in the
actual spread of bubonic plague is still a mooted question.
The housefly has plenty of natural enemies, but they do not seem to
reduce the number to any material extent. One of the most destructive
is a minute fungus which grows inside the fly’s body until it finally
causes death. The dead flies one finds on window panes in the fall,
surrounded by a whitish ring, are the victims of these fungus growths.
There are several species of these fungi; in some cases at least the
attack begins with a spore which attaches itself to the outside of the
body, and grows a long thread-like root which enters the body through
one of the spiracles or breathing pores.
Several species of protozoan parasites have been found in the
intestines of flies, along with a few minute parasitic worms, but
they are not known to cause any great amount of inconvenience. Small
red mites are often seen fastened to flies’ bodies; some of them are
true parasites which suck the juices from the body of their host, and
look very much like the chiggers which annoy the higher animals in the
Southern States. With other mites, according to Howard, “the flies
simply act as aeroplanes to carry the mites from one place to another.
A free ride seems to be the only object for which they have attached
themselves to the fly.”
Spiders, if given an opportunity, destroy a great many flies, but as
the webs are usually destroyed by the housekeeper’s broom they do very
little execution. The little centipede known as the water bug kills a
great many flies, but as it works at night gets little credit for its
good offices.
Hornets are sometimes seen to capture and carry off houseflies, but
it is doubtful if any great number of the pests are killed by these
insects. An English entomologist named Westwood once circulated a story
to the effect that “the Americans, aware of their service in destroying
flies, sometimes suspend a hornet’s nest in their parlors.” A little
later one Benjamin D. Walsh, an American, wrote that “some persons in
America have turned the insect-devouring propensity of the hornets to
good purpose by suspending one of their nests in a house much infested
by the common housefly. In such a situation we have been told that they
soon make a clearance of the obnoxious flies; and so long as you do
not meddle with them they will not meddle with you.” To me these two
quotations are the sheerest nonsense; any one who has any acquaintance
with hornets will find it difficult to visualize an American farmer
intentionally filling his house with hornets for any reason whatsoever.
I have never been able to find anybody who has tried out this method;
if there are any such among my readers I should like very much to hear
from them. Please address me in care of the publisher of this booklet.
The logical way to combat the housefly would be to destroy the eggs and
maggots as we do in the case of the mosquito, but it is not practical
at present. In rural districts, where the dung of livestock is always
lying about, and the human excreta exposed in shallow open closets,
very little progress has been made. Of course, the danger of typhoid
may be avoided by keeping the excreta of typhoid patients where flies
cannot get at it, and the flies certainly could not spread tuberculosis
if no tubercular sputum was exposed. These facts are taken advantage
of in the cities, where there are plenty of flies, but very little
typhoid, because the water closet system is such that flies cannot get
access to the excreta. In communities where there is no adequate sewage
disposal and where flies are plentiful, the individual can only screen
them out of his own dwelling as best he can. Howard estimates that more
than $10,000,000 are spent every year for screen wire in the United
States alone.
Many ingenious devices for destroying flies inside houses are on the
market--poisons, sticky fly paper, fly traps and fly swatters. One
of the most useful of these is sticky fly paper cut in strips and
suspended from the ceiling. This will often clear a room of flies
when the ordinary sheets of the same paper lying flat on a table are
quite inefficacious. In Japanese hospitals, says Howard, “they take
a whole potato and stick it full of toothpicks, put fly paste on the
toothpicks, and hang the potatoes from the ceiling over the patient’s
bed on a cord. The flies all gather on the potato, and when it is full
they throw the potato away and make a new trap. The toothpicks are
placed about one-fourth of an inch apart, and the potato presents the
appearance of a porcupine.”
C. F. Hodge is all for building large traps and placing them out of
doors in early Spring, arguing that a great many newly emerged flies
are thus caught before they reproduce, and that it is better to catch
one fly in the Spring than thousands in the Autumn. Brues even says
that “practical traps whereby fly-larvae in stored manure may be caught
and destroyed before transformation have also been devised.”
Some progress has been made in the treatment of manure piles with
poisons. Howard found that either chloride of lime or kerosene kill
the maggots all right, but the cost of both is prohibitive. Davis
worked with iron sulphate and reported that manure could be cleaned
of maggots and deodorized at a cost of about two cents per horse per
day. Howard, Herns and others have advocated fly-tight pits or bins for
the reception of manure, and these have been adopted in many places,
particularly in California. The regulations of the District of Columbia
specify that all manure must be kept in “covered receptacles,” and it
has been found that a tight-covered barrel suffices for a one-horse
stable. Some workers in the Federal Department of Agriculture have
carried out a series of experiments indicating that borax, hellebore,
and calcium cyanide are highly destructive to maggots in horse manure,
and it is quite probable that some very cheap and simple treatment will
soon be developed.
The proper disposal of human excreta is another problem that is vitally
connected with the checking of germ-laden flies. As Howard says, “the
average person in the large city has no idea of the fact that there
are many comparatively intelligent citizens who in sanitary matters
have not even reached the grade of civilization which demands the
sanitary privy. Stiles, in the course of his great work in the Southern
States, has brought together some startling figures. He is responsible
for the statement that of 4,825 farm houses in six different states
2,664, or fifty-five per cent, have no privies of any kind; of 2,499
houses inhabited by white people, thirty-five and three-tenths per cent
have absolutely none, and of 2,326 inhabited by negroes seventy-six
and eight-tenths per cent have none. And what shall be said of the
condition of a large part--the very great majority--of those which
do exist? The uncared-for privy is still a most important factor all
over the United States, even in portions of our most cleanly cities.”
Herrick points out that “there is no longer any excuse for the old
open box privy, cleaned out once a year. It is a menace to every house
in the vicinity as well as to individuals living perhaps hundreds of
miles away because of its possibilities in contaminating milk. Some
form of sanitary closet must be substituted.” One of the very best is
that designed by Stiles, and described in Farmer’s Bulletin 463, U. S.
Department of Agriculture. The bulletin is free, and the privy can be
built at a cost of five or six dollars.
Another fly which looks almost exactly like the ordinary housefly
is _Stomoxys calcitrans_, usually known as the biting housefly, but
sometimes called the stable fly because of its great abundance about
horses and cattle. The stable fly may be recognized by the fact that it
holds its head higher than the housefly, but Howard says that “the best
way to distinguish between the two flies is to allow them to walk over
your hand; if it bites it is _Stomoxys_; if it does not it is probably
the housefly.” The housefly has no mouthparts adapted for biting, but
the stable fly is provided with a sharp awl-like proboscis, and sucks
the blood from its victims. It is a great lover of direct sunshine,
and, when not engaged about cattle and horses may be seen sunning
itself on walls and fences. In damp weather it invades houses and
verandas, and it is then that the silk-clad ankles suffer. This habit
has given rise to the popular idea that houseflies bite just before a
storm. The bite is painful at the moment, but there is no subsequent
swelling or irritation; the puncture, according to Howard, does not
seem to be poisonous to man, and aside from the pain given it is far
less dangerous than a mosquito bite.
The life history of _Stomoxys_ has been worked out by Newstead, who
found that the creamy-white eggs are laid about sixty at a time in
irregular clusters, usually in manure of some kind, but frequently
in piles of decaying grass or straw. Howard reared the fly from cow
manure, and says that the egg usually hatches in two or three days.
“The larva need not be described,” he says, “because it is so similar
to that of the housefly.” Newstead found that in this stage they lived
from fourteen to twenty-one days, but that the absence of excessive
moisture and the admission of a little light materially retarded
development, which then extended over a period of thirty-one to
seventy-eight days. In the puparium the insect remained from nine to
thirteen days. The development of the species is therefore much slower
than that of the true housefly. It is Newstead’s opinion that the
winter is passed chiefly in the pupal condition.
The stable fly is considered by Austern and others to distribute
various diseases among cattle, but is probably not dangerous to
man. Brues remarks that it was once “thought to be a carrier of
poliomyelitis (infantile paralysis) but it now seems probable that
such is not the case.” Howard says, “I judge from the fact that it is
attracted to human excreta that it may become a carrier of intestinal
diseases,” but it has never been proved to be more than an accidental
agent in this matter.
Bishop reports a great outbreak of this pest in Texas, where they were
found breeding in straw stacks, and caused serious injury to cattle and
horses. A similar case recorded by Lucian Iches of Santa Fe, Argentina,
is described by Howard: “The biting flies swarmed on a large estate
in almost incredible numbers. The cattle were driven nearly crazy by
them. Certain valuable Durham bulls which were observed were covered
with the flies. They had lost their hair in large spots and the skin
was cracking. Monsieur Iches naturally sought at once for the principal
breeding places of the flies, and found them to be in the stacks
of debris from the threshing of wheat and flax. Larvae and puparia
were found by the millions in the lower portions of these piles of
straw, where some fermentation had already begun. The sensible measure
which he recommended was to have this debris burnt within forty-eight
hours after the completion of the threshing, the ashes being used for
fertilizing purposes. It turned out that there was an old provincial
law in the province of Santa Fe ordering the burning of all debris
after threshing, but it had not been carried out during recent years,
and therefore the _Stomoxys_ multiplied until this veritable plague
ensued.”
Another plague of stable flies occurred some years ago in Oregon, but
the life history was not known there and the breeding places were never
found. The severity of the pest’s bite is remarked by Osborne: “It
causes a great deal of annoyance to horses, cattle and other domestic
animals, and is frequently very troublesome to people working in places
where it abounds: Its bite is not poisonous and aside from the pain
given and the possibility of its disseminating disease, it is less
injurious than some other members of the group. When abundant, however,
the annoyance may be very great.” Bold describes the pitiable condition
of cattle bitten by the stable fly: “In some of the severe cases the
joints were so much swollen that the poor animals could not bend their
legs to lie down; and in them the inflammation rose so high as to
cause the loss of the outer skin and hair.”
The cluster fly (_Pollenia rudis_) is a little larger than the
housefly, and appears longer because the wings overlap in such a
fashion as to make the body appear very slender. The thorax bears
many short, yellow hairs, and the grayish abdomen inclines to be
iridescent. During the Summer this fly lives upon flowers and fruits,
and does not come near houses, but the adults seek sheltered places
in the Fall, and spend the Winter in large groups or clusters--hence
the name. When the clustering process happens to take place within a
human habitation the flies become a nuisance. Howard quotes one of his
correspondents from Illinois: “They seem to prefer to occupy the rooms
on the north side of the house and those that are used but little.
They gather in large bunches in the corners and along the edges of the
ceiling. They cannot be driven out like other flies, but must be killed
outright to get rid of them, and when you mash them the odor is like
that of honey. We have tried nearly everything that was recommended to
us, with no effect. It seems impossible to get rid of them, or to keep
them out of the house, for they crawl in through the smallest places in
the windows.”
They enter one by one through small cracks or crevices, and, as one of
Herrick’s correspondents writes, “screens and other devices which work
perfectly in excluding the ordinary fly are useless in keeping these
out.” W. H. Dall, describing the pest at Geneva, New York, states that
“people soon learned to look everywhere; in beds, in pillow-slips,
under table covers, behind pictures, in wardrobes, nestled in bonnets
and hats, under the edge of carpets, etc.”
We are singularly ignorant of the life history of this insect. Macquart
and Desvoidy have found _Pollenia_ larvae in manure, and the Bureau
of Entomology people reared a single specimen from cow dung. Keilin,
however, claims to have discovered the maggot living as a parasite
in certain species of earth-worms. It is said that the adults are
particularly susceptible to the same fungous diseases which attack the
housefly.
The lesser housefly (_Homalomyia canicularis_) is generally regarded by
laymen as an immature specimen of the common housefly, but is really
a distinct species, belonging to a different family altogether. The
housefly, or any other fly for that matter, does not grow at all in the
winged state--the newly emerged adult is quite as large as it will ever
be. The _Homalomyia_ maggot is very different from that of the ordinary
housefly; it measures only about one-fifth of an inch in length, and is
covered with spiny processes, to which the dirt clings and gives the
creature a mottled, dirty appearance. They develop in various kinds of
garbage and manure, being especially partial to human excrement. Hewitt
has found them very abundant in privies, and Herrick remarks that “this
habit of breeding in excreta of various kinds makes the flies dangerous
inhabitants of our rooms. They may act as conveyers of disease germs
quite as readily as the housefly. They are rapid breeders, for a
generation may be produced in two weeks in hot weather.”
The blue-bottle fly (_Calliphora erythrocephala_) has a dull-colored
thorax and a dark metallic blue abdomen. It is sometimes known as the
blow-fly, and lays its eggs on meat and dead animals, or even in sores
upon living creatures. A single female has been known to lay more than
six hundred eggs, and Hewitt says that twenty-three days is sufficient
to produce a generation. The blow-fly ordinarily lives in the open air,
but occasionally gets into houses, particularly in stormy weather.
Herrick remarks that “it has been found frequenting human feces and
for this reason may be suspected of bearing intestinal bacteria, thus
making it a fly to be dreaded.”
The so-called cheese fly (_Prophila casei_) is a little shiny black
fellow which develops in cheese, bacon, ham, chipped beef and the like.
The larva is known as the cheese skipper because of its remarkable
agility. Howard says that it will sometimes jump three or four inches,
and I have myself seen these vigorous little maggots, stimulated by
the heating of their home in a piece of Southern bacon, leap clear out
of the frying pan into the camp fire. The cheese fly is not native to
America and was probably imported in an early shipment of Swiss cheese.
The insect is not particularly dangerous, but as Howard says “it is
well to remember that not only has it been reared from dead bodies, but
that it is also attracted to excreta of all kinds.”
The moth fly (_Psychoda minuta_) is a very fragile little insect whose
broad wings are hairy like those of a moth. It is very common among
weeds, clinging to the under surfaces of leaves, and often enters
houses, passing easily through the ordinary fly screen. According to
Herrick, “the larvae of some of these flies live in cow dung, others in
decaying vegetation, while some live in water, especially sewage water
or drain water from kitchens. We have often seen hundreds of these
moth flies among the weeds overhanging a ditch carrying the drainage
water from a kitchen. We have also seen them in abundance along ditches
carrying sewage water from houses. In the first-mentioned instance they
were always present on the window panes of the kitchen, readily passing
through the ordinary wire screen. Judging them from the places in which
they breed, we would consider them unwelcome guests in our houses.” The
moth flies of Southern Europe bite human beings, and are carriers for a
disease called phlebotomus fever, but the species so far identified in
the United States probably do no particular damage.
The tsetse fly (_Glossina palpalis_), the sole distributor of the
deadly sleeping sickness which has decimated the native population
of equatorial Africa, is a near relative of our common housefly. The
reproduction of the tsetse fly is very different from that of most
insects, however. According to Brues, “the female does not deposit her
eggs, but a single one develops to the fully grown larval condition
before being deposited. This larva soon pupates in the shade beneath
the brush bordering the water where it has been dropped by the parent
fly, and later emerges in the winged adult condition. The pupae
requires such moist shade, and it is apparently for this reason alone
that the flies never occur away from the immediate vicinity of the
water. As a result of their method of development, the tsetse flies
do not multiply rapidly, and even under favorable conditions only one
larva is produced in a ten-day period.... It was thought at first
that by moving all the natives back from the edges of the water, the
flies thus left without opportunities for reinfection, would become
free from trypanosomes (the organisms causing the disease) and that
by isolating and treating cases of the disease in fly-free areas it
would be possible to eliminate them entirely. In conjunction with
this, the cutting of brush, especially about boat landings and
watering places, has been practiced as far as possible. Contrary to
expectations, it has been found that even after three or four years,
infected flies still occur along the uninhabited shores. This led to
experimentation upon animals and it is now known that various wild
antelopes as well as certain domestic animals may act as reservoirs for
the virus of sleeping sickness, which may thus persist in the complete
absence of any human subjects. As a result of this discovery the great
difficulties of combating the disease ... have been vastly increased.”
MOSQUITOES AND DISEASE
The mosquito is nothing more than a small, slender fly, very similar
to the housefly in every essential detail of its structure. There
are about sixty species and varieties in America, but the three
most common and important species are: the ordinary house mosquito
(_Culex pipiens_) which does not carry disease, the malarial mosquito
(_Anopheles quadrimaculatus_) which disseminates malaria, and the tiger
mosquito (_Aedes calopus_) which is a carrier of yellow fever.
The common house mosquito has perhaps no equal as a persistent and
universally damned destroyer of human tranquility. Heartily detested
everywhere, even by entomologists, no serious studies of the life
history were made until comparatively recent years. The female deposits
her eggs upon the surface of still water in boat-shaped masses, each
mass containing from fifty to two hundred eggs. The floating egg-mass
is always large enough to be seen with the naked eye, and often
measures a quarter of an inch in length. The eggs usually hatch in two
or three days, and the larva is the well-known wiggler which swims with
a peculiar jerky motion in every rain-barrel and roadside pool in the
country. The wiggler breathes through a tube near the caudal end of
its body, and usually hangs head downward at the surface of the water,
with the tip of the breathing tube in contact with the air. The food
consists largely of minute organisms collected by two vibrating tufts
of hair about the mouth. After a week or so of this wriggling life, the
larva is transformed into another stage called the pupa, which has a
larger head and thorax, and rides differently in the water because the
breathing tubes have shifted to the upper part of the body. In five or
six days more the skin of the pupa splits open and the adult mosquito
slowly emerges. It usually rests quietly on the floating pupa-skin for
a few moments, and then, as soon as its wings are sufficiently dried,
flies away in search of food and mates.
The male _Culex_ is much handsomer than the female, being provided
with large plume-like feelers or antennae, by which he may be easily
recognized. Another important sex-difference is that the _male doesn’t
bite_, but lives by sucking the nectar of flowers, like a bee. The
female of the species is deadlier than the male, even among mosquitoes,
and it is the female that does the blood-sucking. The mosquito’s beak
consists of several sharp lances inside a sheath, the whole apparatus
admirably adapted to pierce the human skin and transfer human blood to
the stomach of the mosquito. Incidentally some poisonous substance,
probably a salivary secretion, flows into the wound and produces more
or less inflammation and swelling. The _Culex_ or house mosquito, so
far as is known, does not transmit any disease to human beings--it is
detested only because of the pain which follows its bites, and its
intolerable buzzing.
The malarial mosquito (_Anopheles quadrimaculatus_) deposits its eggs
singly on the surface of the water, never in rafts like those of the
house mosquito. The eggs are very seldom found in barrels or tubs about
houses--the _Anopheles_ prefers ditches, or creeks, or the shallows of
slowly flowing rivers. The malarial larvae do not hang head downward at
the surface as the _Culex_ wigglers do, but lie flat just beneath the
surface film, and may be identified by this characteristic horizontal
position. The _Anopheles_ pupa does not differ greatly in appearance
from that of the house mosquito. The adult is somewhat larger than
_Culex_, and the wings are gray-spotted instead of clear. Another
important difference is this: _Culex_ alights and rests with its body
parallel to the surface which supports it, while _Anopheles_ rests with
its body at an angle--head down, tail up. Herrick says that he has seen
them “clinging to the ceiling of a horse stall by their four front
legs, with their bodies hanging almost straight downward.”
It has been known for a long time that malaria, otherwise known as
ague, or chills-and-fever, was connected in some way with stagnant
water. It was obvious enough to everybody that the disease was most
prevalent in low, swampy regions, and most people regarded it as a
result of poisonous gases which somehow arose from the surface of the
waters. The word _malaria_ means _bad air_. It was later discovered
that the real cause of the disease is a microscopic bit of jelly-like
protoplasm--a protozoan parasite which lives in the red cells of the
blood. Brues tells us that “the protozoan blood parasites which cause
malaria were first demonstrated many years ago, in 1880, by a French
surgeon, Laveran, who discovered them in the blood of persons suffering
from malaria. Five years later an Italian, Golgi, distinguished
three kinds, each associated with one of the more familiar types of
malaria. They were found to go through a regular life cycle in the red
blood corpuscles and, from analogy with other known protozoa, it was
suspected that in addition to their non-sexual generations in the human
blood there must be a sexual development in some cold-blooded animal.
Manson was led to suspect that some insect might be the secondary
host and, working on this hypothesis, Ross in India first found the
malarial parasites in a certain kind of mosquito in 1898. He had
worked for nearly three years with a common mosquito belonging to the
genus _Culex_ without result, but finally in a mosquito of the genus
_Anopheles_ was able to trace the development of the parasite. His
epoch-making discovery has since been amply confirmed and extended by
experimental proof until we now know that the various types of malarial
blood parasites complete their life cycles in anopheline mosquitoes,
the latter acting as the sole carriers of the disease.”
Malaria, then, is acquired in one way only, and that is through the
bite of the malarial mosquito. A mosquito sucks a little blood from a
malarial patient, this blood containing some of the protozoan germs
which are the immediate cause of the disease. In the stomach of the
mosquito the parasites reproduce sexually, penetrate the stomach
walls, and proceed finally to the salivary glands, from which position
they are injected into the blood of the next victim of the mosquito’s
blood-lust. The parasites reproduce asexually in the man’s red blood
corpuscles, and then burst out by millions into the liquid part of the
blood. This happens simultaneously in all parts of the body, and the
patient is shaken by the chills characteristic of the disease. Some
varieties of the germs reproduce every two days, producing what is
known as tertian fever; other types form spores every three days, and
the resulting disturbance is known as quartan fever. After a while male
and female germs appear in the patient’s blood plasma, but these never
develop unless the sufferer is bitten by another mosquito. When this
occurs, the sexual germs pass into the mosquito’s stomach, reproduce
sexually, and are distributed as described above. Another man bitten,
more non-sexual reproduction, more chills and fever, and so on _ad
infinitum_.
A healthy person may, of course, be bitten by _Anopheles_ and have
a great many malarial germs in his body without developing malarial
fever, as they sometimes lie dormant in the blood without reproducing
at all. Ross has estimated that “something like a quarter of a billion
of them must be present to produce fever.” The more infected mosquitoes
that bite one, the larger the number of germs that will be introduced,
and the more severe the disease. The essential result of all the
investigations is concisely stated by Herrick: “Malaria is caused by a
minute animal parasite that lives within the red blood corpuscles of
human beings. The parasite destroys millions of the red blood cells
that are so necessary to life, and, in addition, secretes certain
poisonous substances known as toxins, which lodge in various parts of
the body.... Since this parasite lives only in man and the mosquito,
it can get from one person to another only through the agency of these
insects. In other words, a person once free from the malarial parasite
will remain free just so long as the bites of certain species of
mosquitoes can be avoided.” One acquires malaria in one way only, and
that is by being bitten by _Anopheles_ mosquitoes.
[Illustration:
Fig. II. Malaria and its Carrier. A, the malarial mosquito,
_Anopheles quadrimaculatus_. B, chart showing the seasonal prevalence
of malaria in the United States.
]
The tiger mosquito (_Aedes calopus_) is not native to the United
States, but has been introduced from the tropics. Today, however, it
is widely distributed in the Southern States, and has been found as
far north as New York. The eggs are laid singly or in small groups in
stagnant water, and hatch in from twelve hours to three or four days.
The larval life lasts about nine days, and the larvae are much more
active than the other mosquito wigglers. The tiger mosquito is not
often found in the country, but always near human dwellings, and it
prefers to deposit its eggs about houses, in vessels containing only a
little water--tubs, cisterns, rain barrels, old tin cans and the like.
The pupa state lasts only about two days, and the whole development
from egg to adult is sometimes passed in less than a fortnight. The
adult is considerably smaller than the other mosquitoes described here,
and is conspicuous for its white banded legs, and the prominent white
stripes on the thorax.
In 1881 a man named Carlos Finlay claimed that yellow fever was
transmitted by mosquitoes, but nobody paid any serious attention
to this novel theory, as everybody thought yellow fever was highly
contagious--carried about in the clothing like smallpox. In 1900 a
commission of United States army officers--Drs. Reed, Carroll, Lazear
and Agramonte--went to Cuba to make an experimental study of the
situation there. The procedure and results are concisely summarized by
Herrick: