_The bot-fly of sheep_ (_O. ovis_) resembles an overgrown house-fly. Its
general color is brown, and it is apparently lazy, flying about very
little. This bot-fly makes its appearance when the warm weather begins, and
deposits live larvae in the nostrils of sheep. This act is greatly feared
by the animals, as shown by their crowding together and holding the head
down. The larva works up the nasal cavities and reaches the sinuses of the
head, where it becomes attached to the lining mucous membrane. In the
spring, when fully developed, it passes out through the nasal cavities and
nostrils, drops to the ground, buries itself, and in from four to six weeks
develops into the mature fly.

SYMPTOMS OF BOT-FLY DISEASES.--The larvae of the bot-fly of the horse do
not cause characteristic symptoms of disease. Work horses that are groomed
daily are not hosts for a large number of "bots," but young and old horses
that are kept in a pasture or lot and seldom groomed may become unthrifty
and "pot bellied," or show symptoms of indigestion.

Cattle suffer much pain from the development of the larva of the _H.
lineata_. During the spring of the year, the pain resulting from the
presence of the larvae beneath the skin and the penetration of the skin is
manifested by excitement and running about. Besides the loss in milk and
beef production, there is a heavy yearly loss from the damage to hides.

The parasitic life of the bot-fly of sheep results in a severe catarrhal
inflammation of the mucous membrane lining the sinuses of the head, and a
discharge of a heavy, pus-like material from the nostrils. The irritation
produced by the larvae may be so serious at times as to result in nervous
symptoms and death.