PARASITIC INSECTS AND MITES 235 



egg reaches the mouth through the animal licking the part. The 

 saliva dissolves the shell of the egg and the larva is freed. It 

 then migrates from the gullet, wanders about in the tissue until 

 finally it may reach a point beneath the skin of the l)ack. Here 

 the larva matures and forms the well-known swelling or warble. 

 In the spring of the year it works out through the skin. The 

 next stage is spent in the ground. The pupa state lasts several 

 weeks, when the mature fly issues forth. 



Tlie hot-fly of sheep (0. 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 gTound, buries itself, 

 and in from four to six weeks develops into the mature fly. 



Symptoms of Bot-fly Diseases. — The larva? 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 larvae 

 of the II. llneata. During the spring of the year, the pain re- 

 sulting from the presence of the larva? 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 



