Following are the leading external parasites of cattle, horses, sheep and swine (for parasites of poultry, see page 377).

Cattle. Ox bot-fly or warble-fly (Hypoderma bovis and H. lineata). — Large lumps or warbles along the animal's back filled with pus, within which a large, thick-bodied maggot develops. When full grown these maggots, about an inch in length, work their way out through the skin, fall to the earth, and there after a time transform to a large blackish fly with yellow markings. The flies glue their eggs to the hair of the host, usually around the heels and flanks. The eggs are licked off by the animal, hatch in the mouth or oesophagus, and the larva bores its way through the tissues until it comes to lie under the skin along the back. The cattle have an instinctive dread of the flies, and are thrown into a panic by their presence. Badly infested animals lose flesh, and the flow of milk is greatly reduced ; the holes made in the skin also decrease the value of the hide.

Treatment. — Squeeze out and crush the grubs and disinfect the sore. The practice of killing the grub under the skin by the application of grease or kerosene is more liable to cause an infection from the decaying maggot and produce a serious sore.

Horn-fly (Haematobia serrata). — Flies considerably smaller than the house-fly, which they closely resemble in shape and color. They attack cattle in great numbers, clustering on any part of the body and sucking blood. They have the peculiar habit of resting in dense clusters on the horns. The eggs are laid and the maggots develop in fresh droppings, and the transformation to the fly takes place in the ground.

Treatment. — Spread out or mix with lime the manure as soon as deposited, to prevent the development of the maggots. Let hogs run with the cattle; scatter the manure. Spray the animals with crude oil emulsion often enough to prevent attack, or apply train oil or a mixture of two parts of crude cottonseed oil and one pint of pine tar. The last two may be applied with a large brush, and remain effective for four or five days. Where the flies have produced sores, treat them with a weak solution of carbolic acid. On the range where large numbers of animals are to be treated, dip them in a dipping vat provided with a splash-board which will throw the spray down on the animal and kill most of the flies. Use any of the oily dips recommended for the Texas-fever tick.

Cattle lice (Haematopinus spp. and Trichodectes scalaris).— Cattle are especially liable to become infested with lice during the winter and early spring. They acquire a generally unthrifty look, and the flow of milk is greatly lessened. On young stock the injurious effects are more noticeable ; lousy calves are thin and do not make the proper growth.

Treatment. — When the weather will permit, spray or wash infested animals with a 10 per cent kerosene emulsion or the nicotine-and-sulfur sheep dip as used for sheep scab.

Southern buffalo-gnat (Simulium pecuarum). — A small black gnat or punkie occurring in the lower Mississippi Valley, where it causes immense loss to the live-stock interests. The larvae are aquatic, and are able to develop only in swiftly running waters. The gnats appear in great swarms in early spring and attack cattle, mules, horses, sheep, and other animals in countless numbers. They feed by sucking the blood and at the same time inject a poison into the wound, causing great distress and producing an acute inflammation. Animals in poor condition from exposure or lack of food are frequently killed.

Treatment. — Protect the animals by smudges producing a dense smoke, or keep them in dark stables until the swarms of gnats have disappeared. Working teams can be protected by using train-oil or the cotton-seed oil and tar mixture advised, under Horn-fly. To reduce the irritation caused by the bites, rub the animal thoroughly with water of ammonia and give internally a mixture of 40 to 50 grains of carbonate of ammonia in a pint of whiskey, and repeat the treatment every three or four hours until relieved.