508 



DISEASES OF CATTLE. 



of this fly and not infrequently appear terror stricken. The eggs are 

 attached singly, one egg to a hair near its base^'> 



The eggs of the warble flies hatch as a rule in about a week, Ithe 

 time varying with local conditions. The young warble is about 1 mm. 

 (2V inch) long, fit crawls to the base of the hair and burrows into 

 the hair follicle. The entrance of the larvae frequently causes sudden 

 appearance of swellings. The larvae of H. hovis in entering the skin 



Fio. 6.— The warble fly {Uypoderma lineatum): a, adult female; 6, eggs attached to a hair, X 25; c, larva 

 as seen in egg; d, larva from esophagus of an ox; e, later stage of larva from beneath the skin of the back; 

 /, larva at the stage when it leaves the back of cattle and falls to the ground— all enlarged (after Riley). 



rarely ''cause a flow of serum or pus formation, but those of H. linea- 

 tum commonly cause a considerable flow of serum with pus forma- 

 tion resulting in a matting of the hair on affected areas of the skin. 

 The warbles after penetrating the skin migrate through the body 

 and ultimately reach the backs of the cattle, H. lineatum usually 

 appearing there in northern latitudes about the middle of December 

 and H. hovis about a month later. During their migi-ations, before 

 they reach the back, the young warbles spend a considerable period 



