Part 22

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.

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.

FIG. 122.—Horse Louse (Hæmatopinus macrocephalus), magnified ten times. ]

CLASS II.: =MYRIOPODA= (CENTIPEDES AND MILLIPEDES).

Respiration by tracheæ, as in insects. The body consists of a head and a large number of very similar segments, each of which possesses limbs. One pair of antennæ.

This class is divided into two orders: (1) that of =Centipedes= (Chilopoda), with mouth-parts adapted for seizing prey, and one pair of legs to each segment; (2) that of =Millipedes= (Chilognatha), adapted for devouring substances resembling humus, also the parts of plants; and two pairs of legs to each segment. Here belong, above all, the =Snake Millipedes= (Julus) or “False Wireworms” (Fig. 123), of which several species eat out germinating seeds (peas, beans, mangolds, and beet), and also attack juicy plant parts (potatoes, turnips, carrots). Seedlings may be protected by using potatoes to draw away the millipedes.

FIG. 123.—Common Snake Millipede (Julus terrestris), somewhat magnified. ]

CLASS III.: =ARACHNOIDEA= (SCORPIONS, SPIDERS, MITES).

Air-breathing (by ordinary or modified tracheæ); the lower forms breathe with the skin. Body at most consists of two chief regions, since head and thorax are always fused together, making up a cephalothorax (Fig. 124); but this may again be united with the always unsegmented abdomen into a single piece (Fig. 127). The last is the case with the mites, in which, therefore, the characters of segmented animals can only be recognized in the limbs. In the true spiders (Fig. 124) the body consists of cephalothorax and abdomen. Arachnids have always four pairs of legs, which, in the true spiders, are attached to the cephalothorax, in the mites to the front part of the unsegmented body.

FIG. 124.—A Spider (Salticus scenicus). ]

The chief Orders belonging here are: (1) true =Spiders= (Araneida); (2) =Scorpions= (Scorpionida); (3) =Harvestmen= (Opilionida); (4) =Mites= (Acaridea). Only the last contains species of importance agriculturally.

ORDER: Acaridea (MITES).

Small arachnids, in which the cephalothorax and abdomen are fused together into one piece (Fig. 127). The just-hatched young have three pairs of legs, the adults, of course, four.

Family: =Acaridæ= (True Mites).

Soft skin. No tracheæ, no eyes. Legs short, often with a sucker at the end. Here belong the =Cheese Mite= (Acarus siro), the =Meal Mite= (Tyroglyphus farinæ), and several other species living in dead organic substances; also—

The =Itch=, or =Mange Mites=.

These live as parasites on or in the epidermis, and cause the itch or mange (scabies) in man, as well as in several domestic animals. By means of the structure and habits three genera are distinguished:—

1. Digging, blood-sucking mange-mites living in the skin (Sarcoptes);