(Fig. 120, C) is about one-tenth of an inch long, shining black, with a
metallic sheen. Legs short, feet yellow. Maggot (Fig. 120, A) yellowish
white, about one-eighth of an inch long, cylindrical, and tapering in
front. Usually three generations. 1. The maggots of the first generation
are found during May, in the lower part of the haulm of summer corn
(especially oats and barley); the plants attacked either die off
entirely, or some haulms develop further, remaining small, however, and
yielding only a few light grains. The base of the haulm thickens
abnormally, but the growth in length is always small; the leaves, too,
grow badly, first becoming yellowish at the tip, and then entirely
yellow or reddish. The symptoms of disease are exhibited to a less or
greater extent, according as few or many (even up to ten) maggots
inhabit the base of a plant. The shining brown pupæ (Fig. 120, B) are
found in the lower part of the haulm, or between the leaf-sheath and the
haulm (Fig. 120, D). The adult insect is on the wing at the end of May
and in June. The first generation often appear on wild or meadow
grasses, and are chiefly seen on summer corn when this is sown late or
develops slowly. 2. The maggots of the second generation are found in
average cases during July, on the as yet scarcely ripe grains of late
summer corn, principally those of oats and barley, often occurring also
in the haulms of grasses. They keep between the awns, and suck the
juices of the soft developing grains, which are rendered incapable of
growth, and in any case remain light. The maggots of the second
generation develop more quickly than those of the first or third; they
are mature in three weeks. The pupa rest is very short, and the flies
appear in August, September, or October. They lay their eggs on the
leaves of winter corn or winter grasses, and from these eggs are
developed (3) the maggots of the third generation, which are to be
found, during September and October, in the heart of winter corn and
grasses, injuring these plants in exactly the same way that the maggots
of the first generation injure the summer corn. The insect passes the
winter as a pupa in winter corn plants or grasses. It is but very rarely
that all _three_ generations infest the corn of any particular region;
as a rule, only the first, second, or third generations do this, or the
first _and_ third; in such cases the other generations live on grasses.
_Remedies_: Extermination of the insect is impossible, since it can
always go from corn to grass plants. Oats and barley are almost always
attacked in spring, if in the immediate neighbourhood there is winter
rye inhabited by the maggots, for the flies, when they emerge the next
spring, seek out the summer corn. This may, however, be made impossible,
or at least difficult, if a field of peas, clover, lupines, rape, or
some other crop not of gramineous nature, is interposed between fields
of winter corn and those of oats, barley, or similar late sown crops of
summer corn. Sowing the summer corn (especially oats and barley) as
early as possible.
[Illustration:
FIG. 120.—The Frit Fly (_Oscinis frit_, L.): A, larva; B, pupa; C,
fly; D, a diseased corn plant, as appearing in spring,—the larvæ and
pupæ are seen of the natural size in the lower part of the plant.
]
Family: =Syrphidæ= (_Hover_ or _Hawk Flies_).
Chiefly includes brightly coloured flies, marked with yellow or red and
black bands or patches (Fig. 67), and flying rapidly with a buzzing
noise. They can remain suspended at the same point in the air by moving
their wings up and down with great rapidity. A few of them resemble the
humblebee in their thick covering of hair; others, with yellow and black
abdomen, look like wasps (_Syrphus_). The proboscis is adapted for
sucking, but not for piercing; these flies suck their food from flowers.
They are fond of hovering in the air in sunny places. The legless larvæ
vary, according to species, in their habits, and consequently in their
structure. Some (those of the =Drone Flies=, _Eristalis_) live in
stagnant water; others (_e.g._ those of _Eumerus lunulatus_) live in
onions, which they hollow out; while some, again, develop in rotten
wood, etc. The maggots of the =Aphis-eating Flies= (_Syrphus_), however,
feed on insects, chiefly aphides, which they suck out completely. They
are elongated, tapering in front, thickened behind, move like leeches,
and vary much in colour (green, yellow, brown, chequered), according to
the species. As they grow quickly, and consequently more than one
generation is found each year, and as they are very voracious, we must
look upon them as powerful allies for the extermination of aphides.
Family: =Stomoxydæ= (_Stable Flies_).
In many points the stable flies resemble ordinary flies, but their
mouths are adapted for piercing. Their painful bites make them known to
every one as pests to human beings and cattle. Here belongs the common
=Stable Fly= (_Stomoxys calcitrans_), a form often confounded with the
house fly, but distinguished from it by a sharp proboscis projecting at
right angles, besides which the abdomen is more of a yellowish grey. The
maggots usually live in dung. Two generations yearly: the first flies
about in March; the second, and much more numerous one, in August and
September. _Remedies_: Cp. p. 165.
Family: =Œstridæ= (_Bot Flies_).
Medium-sized or large flies (Fig. 121), with thick hemispherical heads,
and mouth-parts not strongly developed. The antennæ can be drawn back
into deep pits. The hot flies make a buzzing sound during flight. The
headless, twelve-ringed maggots live in the bodies of various mammals.
Their skin is provided with numerous wart-like projections, or circlets
of spines. When very young the maggots are elongated and cylindrical,
and then possess a mouth-hook, which disappears during the later moults.
As soon as the maggots are fully developed they leave the body of the
animal they inhabit, and let themselves fall to the ground, where they
become pupæ within the shrivelled larval skin.
The following genera are distinguished: =Warble Flies= (_Hypoderma_),
and =Bot Flies= (_Œstrus_ and _Gastrus_, or _Gastrophilus_). To the
first-named genus belongs the
=Ox Warble-fly=, or =Ox Bot Fly= (_Hypoderma bovis_),
two-fifths of an inch long, black. Hair: whitish yellow on the head;
reddish yellow on the fore part of the thorax, black on the hinder part;
grey on the fore part of the abdomen, black in the middle, and reddish
yellow behind. Legs black. Wings brownish, not quite transparent.
On the wing during summer (June to September). As soon as the cattle
hear the flies buzzing around (especially on hot days) they become very
restless, run about as if mad, and even plunge down steep places. Young
cattle are selected for egg-laying; the elongated white eggs are fixed
separately to hairs. The maggot, elongated when first hatched,
perforates the skin, and gets into the subcutaneous connective tissue,
where it does not, as a rule, keep to any one place, but wanders here
and there, sometimes penetrating the flesh, or even entering the spinal
canal. It always, however, wanders back again later on into the
subcutaneous connective tissue, where it gives rise, during the winter
or the following spring, to one of the well-known tumours, or “warbles.”
After fixing on a definite spot, it moults, becoming broader, and of a
yellowish white colour. The maggot first causes an increased flow of
blood to the part, and then inflammation. An excavation filled with
matter is thus developed, and there is gradually formed a connective
tissue sac communicating with the exterior by a minute tube. In spring,
or early summer, the warble, which is visible externally, has reached
the size of a pigeon’s egg; the maggot meanwhile becomes first greyish
yellow, then brown patches appear, and lastly it assumes a dark brown
colour, is an inch long or rather more, and somewhat swollen. It is now
ready to pass into the resting stage, crawls out, and lets itself fall
to the ground, where, within the larval skin, it becomes a black pupa
four-fifths of an inch long, from which, about four weeks later, the fly
creeps out. _Damage done_: If the warbles occur only in small numbers on
an animal, its health is not much affected, though this must undoubtedly
be the case if there are many, say fifty, or even up to a hundred, in
the same animal. In such cases the yield of milk will be considerably
diminished. Holes, too, are present in the skin, which, though they may
close again, if the animal remains alive, always leave a thin place. The
outer surface of meat from animals infested with warbles is dirty
yellow, flaccid, or even soft and jelly-like (“licked beef”); it must be
scraped off. _Enemies_: Starlings settle, in spring, on the backs of
infested cattle, and seize the parasites with their beaks. Starlings,
rooks, and wagtails destroy the maggots ready to become pupæ, as they
lie on the ground. _Remedies_: Washing the back, shoulders, and loins
with vinegar extract of walnut leaves during the summer, to keep away
the bot flies. In spring: squeezing out the maggots from the warbles,
having previously opened them, when necessary, with a penknife. If the
warble is “ripe,” _i.e._ if it has opened so far that the black hinder
end of the maggot can be seen, the opening may be stopped with fat or
cart-grease, by which the larva will be killed where it lies.
The =Sheep Bot Fly= (_Œstrus ovis_),
two-fifths to three-quarters of an inch long, yellowish grey, almost
hairless; head large, round, reddish; thorax grey, with small black
warts; abdomen yellowish white; legs short, bright; wings of a glassy
clearness. The flies are found (in September) on the walls of
sheepfolds, and in woods near which sheep graze. On sunny days the
female flies round the sheep, in order to deposit her brood upon them.
The sheep threatened press their nostrils to the ground, though this is
not of much use. The maggots are hatched while still in the body of
their mother, and are deposited by her on the margins of the nostrils.
These little maggots creep about on the mucous membrane lining the
internal cavities of the nose, causing intolerable itching. The sheep
try to get rid of the intruders by shaking their heads and rubbing their
noses on the ground. The maggots, however, creep further into the nasal
cavities, and get into the hollows of the frontal bone and upper jaw,
perhaps even into the horns. In these places they feed on the fluid
which their presence causes the mucous membrane to give out in large
quantities. The maggots remain as such for nine months, during which
time they alter their shape in various ways. Those just born are white,
one-twenty-fifth of an inch long, while those which have reached the
length of two-fifths of an inch are yellowish white. Individuals ready
to become pupæ are about an inch long, yellowish brown, with dark
transverse lines; they wander back to the nasal cavities and thence to
the exterior, often being expelled by sneezing. In the soil they become
pupæ, first of a brown, then of a black colour, within the larval skin;
the flies emerge in six or seven weeks. Different maggots develop at
different rates, according to the nature of the cavities into which they
penetrate.
The maggots cause the disease known as “false gid,” which appears most
obviously from March to May; at this time the parasites are tolerably
well developed. They irritate the mucous membrane of the cavities of the
head in which they live, causing an unusually large flow of blood to
these parts, as a result of which the mucus secreted in the nose
increases largely in quantity (sneezing, snuffling), and the brain
begins to work abnormally (uneasy movements of the head, high lifting of
the feet; in worse cases, rolling of the eyes, gnashing of the teeth,
and foaming at the mouth). The sheep have also an intolerable itching of
the nose, which they rub in consequence on the ground, against posts, or
their own legs; besides this, there may be inflammation of the eyelids
and increased secretion of tears. They are also apt to grow very thin.
The disease is more frequent, and the symptoms severer, in young than in
old sheep. False gid may cause death; the animal is cured, however,
after the maggots have crept out. _Preventive Measures_: Keeping the
sheep away from the edges of woods, avenues, etc., where the flies live
by preference. When sheep are killed, the maggots coming from the head
should be collected and destroyed. Smearing the margins of the nostrils
with tar, or rubbing them with walnut leaves, before the sheep go to
pasture in the morning. For sheep, which in late summer rub their noses
up and down tree stems, walls, hedges, or their own legs, substances
that cause sneezing may be employed, _e.g._ cheap snuff, which is best
introduced into the nose by means of a quill-feather. Later on, when the
maggots have passed from the nasal cavities into the frontal sinuses,
etc., sneezing does no good. Operations seldom succeed in removing all
the maggots.
[Illustration:
FIG. 121.—Horse Bot Fly (_Gastrus equi_): _a_, egg on a hair, strongly
magnified; _c_, younger (magnified), and _b_, older larva; _d_,
opened pupa case; _e_, fly.
]
The =Bot Flies= (_Gastrus_, or _Gastrophilus_) live in various parts of
the stomach (in left side of horse’s stomach) and intestine. I give,
first of all, a compressed tabular view of the external characters and
mode of life of the four British species. (See next page.)
_Diseases caused by Bot Flies._—The maggots bore into the walls of the
stomach and intestines until they reach the layer in which the
blood-vessels, lacteals, and lymphatics ramify; they then suck the
juices found in these vessels, and also serous fluids. In small numbers
they are often almost harmless, but when a great many are present they
hinder the secretion of the digestive juices. They may also set up
inflammation of the intestinal coats, or may cause death by internal
bleeding if they perforate the wall of an artery. In foals they often
bore right through the wall of the intestine, and enter the abdominal
cavity, where they may set up inflammation of the peritoneum or of the
mesentery. There may be as many as a hundred or two hundred maggots in
the stomach or intestine, and they then cause, at the very least,
digestive disturbances and colic. If the maggots (_G. nasalis_) get into
the windpipe (or larynx) they interfere with the breathing; if into the
gullet, with swallowing. In either case death may ensue (winter, early
spring). _Remedies_: Killing the flies as they lay their eggs. Removing
the eggs by brushing, combing, and washing; the last is best done with
warm water, to which some caustic potash is added. Rubbing the lips and
nostrils, neck, chest, and fore legs with walnut leaves, or a decoction
of the same.
────────────────────┬──────────────────┬──────────────────┬──────────────────
SPECIES. │ FLY. │ EGG. │ MAGGOT.
────────────────────┼──────────────────┼──────────────────┼──────────────────
=Horse Bot= │½ to ⅖ inch, very │White: on the │At first flesh
(_Gastrus equi_). │ hairy, like a │ hairs of the │ red, then
│ humblebee; │ mane, neck, │ yellowish-brown.
│ brownish yellow.│ chest, fore │ Lives in the
│ Fore part of │ legs, and hind │ stomach of the
│ thorax with │ feet of horse. │ horse, often in
│ yellowish-brown,│ │ large numbers.
│ hind half with │ │
│ black hairs. │ │
│ Abdomen with │ │
│ brown hair in │ │
│ front, │ │
│ brownish-yellow │ │
│ behind. │ │
=Cattle Bot= │Male about ½ inch,│Black: on the same│First yellowish
(_Gastrus_ │ brown, closely │ parts of the │ grey, then
_pecorum_.) │ covered with a │ horse’s body as │ blood-red. First
│ mixture of │ in the preceding│ in the small
│ yellowish and │ species; │ intestine, and,
│ black hairs. │ exceptionally on│ for some time
│ Wings │ the hairs of │ during June or
│ smoke-coloured. │ horned stock. │ July, in the
│ Female rather │ │ rectum of the
│ larger. Head, │ │ horse. When
│ thorax, and │ │ ready to become
│ first segment of│ │ pupæ, they creep
│ the abdomen with│ │ out of the anus,
│ colour and hairs│ │ to the margin of
│ as in the male; │ │ which, however,
│ rest of abdomen │ │ they may remain
│ black, and │ │ sticking for
│ tapering │ │ some time.
│ posteriorly. │ │
│ Wings │ │
│ smoke-coloured. │ │
=Red-tailed= =Bot= │About ⅖ inch. Fore│Black: on the lips│First red, then
(_Gastrus_ │ part of thorax │ and margins of │ bluish-green. To
_hæmorrhoidalis_).│ dark fawn │ the nostrils in │ begin with, in
│ colour, with │ the horse. │ the cavities of
│ bright yellow │ │ the nose or
│ fur-like hair; │ │ mouth, in the
│ hinder part │ │ horse, very soon
│ black. Abdomen │ │ in the stomach
│ shining black, │ │ or small
│ with yellowish │ │ intestine,
│ white hair in │ │ remaining there
│ front, black in │ │ several months;
│ the middle, and │ │ then, a few
│ orange yellow at│ │ months longer,
│ the tip. Wings │ │ in the rectum.
│ of glassy │ │ Exceptionally,
│ clearness, with │ │ the maggots
│ dark brown │ │ remain in the
│ veins. │ │ gullet for some
│ │ │ time.
=Nose Bot= │Nearly ½ inch (not│White: on the lips│Yellowish white.
(_Gastrus_ │ including the │ and margins of │ In the first
_nasalus_). │ long ovipositor │ the nostrils in │ part of the
│ of the female). │ the horse. │ horse’s small
│ A fine but close│ │ intestine, near
│ covering of │ │ the aperture of
│ hairs; │ │ the stomach;
│ variegated, not │ │ exceptionally in
│ always evenly │ │ the nasal
│ covered with │ │ cavities,
│ hair, especially│ │ gullet, and
│ not on the black│ │ stomach.
│ abdomen (partly │ │
│ white, black, │ │
│ orange yellow, │ │
│ yellowish grey);│ │
│ thorax a shining│ │
│ blackish brown, │ │
│ covered with │ │
│ fine, golden │ │
│ yellow hair. │ │
│ Wings clear as │ │
│ glass, widely │ │
│ spread when at │ │
│ rest. │ │
────────────────────┴──────────────────┴──────────────────┴──────────────────
Family: =Pupipara= (_Louse Flies_).
Body flat and broad; skin leathery and tough. Fore legs curved, adapted
for climbing among the hairs. Some (_e.g._ the Forest Fly) have a pair
of wings, others (the Sheep Louse Fly) are wingless. They bring forth
living maggots, each time one only, which is ready to become a pupa
immediately. They reproduce several times. Here belong: 1. The =Forest
Fly=, =Spider Fly=, or =Flat Fly= (_Hippobosca equina_), about one-third
of an inch long, brown, with broad abdomen, and two broad stumpy wings.
Occurs in summer and early autumn, chiefly on horses, especially near
the anus, on the belly, and on the flanks. It sucks blood, and irritates
by running about on the body. Seldom flies. 2. The =Sheep Louse Fly=,
wrongly called “sheep louse” and “sheep tick” (_Melophagus ovinus_);
about one-fifth of an inch long, wingless, rusty yellow, with brown
abdomen, very hairy. Climb slowly about among the wool of the sheep, and
suck blood. Their excrement may colour the wool green. Lambs especially
are much hindered in their growth by this fly. The fleece is also
damaged, for the itching set up by the insect forces the animal to rub
itself against things so that the wool gets pulled out. The flies are
chiefly found on meadow sheep; but relatively few in winter. The
parasites leave the body of their host for the purpose of reproduction,
and lay their maggots, which at the time of birth are nearly one-sixth
of an inch long, under little bits of earth or heaps of dung. When sheep
are kept in folds no permanent result can consequently be expected from
the use of any remedy if, at the same time, the fold and all its
contents are not kept clean. The walls must be cleansed, and washed with
caustic potash, to which carbolic acid has been added. _Curative
Washes_: A decoction of walnut leaves and vinegar. Turpentine, soapsuds,
decoction of tobacco. Washes containing arsenious acid (_e.g._ Bigg’s
Improved Sheep and Lamb Dipping Composition) must be used with caution;
unpalatable substances may be added, so that the sheep will not lick
them, or else a muzzle may be employed.
NINTH ORDER: =Aphaniptera= (FLEAS).
Body strongly compressed laterally. Head small. Mouth-parts adapted for
sucking and biting. Legs long, especially the last pair. They possess
the power of springing. Wingless. Complete metamorphosis. Larva
worm-like, legless, hard-headed. The =Dog Flea= (_Pulex serraticeps_),
which only occasionally passes on to human beings, lives on dogs and
cats. _Remedy_: Sprinkling the moistened hair with Persian insect powder
or powdered parsley seed.
TENTH ORDER: =Parasita= (LICE).
Body flattened. Legs adapted for climbing among hairs and feathers, as
the last joint of the foot is hook-shaped, and can be bent back against
the preceding joint; a hair can thus be held fast between the two
joints. Eyes absent or ill developed (simple). Wingless. The eggs
(“nits”) are fastened by the mother louse to the hairs of the host; the
young lice resemble the old ones in almost all particulars; there is no
true metamorphosis. All lice have a kind of proboscis, which can be
protruded and retracted, and upon which are placed the mouth-parts,
which enable it to be used for sucking or biting. According to the last
feature a distinction can be drawn between true or blood-sucking lice
and biting lice or fur-eaters, which devour small scales derived from
the skin or else bits of hair and feathers. Lice multiply very rapidly
on the bodies of human beings and animals when insufficiently cleansed,
and under these circumstances more on sick and ill-nourished individuals
than on those which are healthy and well nourished. It is obvious that
the true, blood-sucking lice usually injure their host more than the
biting lice, which, however, especially when present in large numbers,
may cause an intolerable and injurious itching by their movements here
and there. _Preventive Measures_: Suitable feeding and treatment. Proper
care of the skin. _Remedies_: Repeated combing with a comb which has
been dipped into a solution of soda. Rubbing the badly infested spots
with soft soap and soda, washing them out after twenty-four hours. Among
other washes are—6 parts soft soap, 1 part benzine, 10 to 15 parts
water; or tobacco water, 1 part of common tobacco in 20 to 25 parts
water; arsenious acid, in various mixtures, _e.g._ in Bigg’s Composition
(p. 193). Employ the muzzle.
[Illustration:
FIG. 122.—Horse Louse (_Hæmatopinus macrocephalus_), magnified ten
times.
]