ANIMAI. PARASITES OF CATTLE. 

 GRUBS, WARBLES, BOTS. 



515 



The common parasites known as grubs, warbles, bots, etc. (fig 11), 

 found under the skin of the backs of cattle, where they form more or 

 less conspicuous lumps during the latter part of w^inter and spring, 

 are the larvae of a fly known as the heel fly or warble fly. This fly 

 {Tlypoderma lineatum) is about one-half inch long, very hairy, and 

 somewhat resembles a small black bee. The flies appear early in the 



Fig. 11. — The warble fly (Hypodcrma lineatum) : a, adult female; t, eggs attached to a 

 hair, X 25 ; c^ larva as seen in egg ; d, larva from esophagus of au ox ; e, next stage of 

 larva from beneath the skin of the back ; f, larva at the stage when it leaves the back 

 of cattle and falls to the ground — all enlarged (after Riley). 



summer and are more or less prevalent until the beginning of cold 

 weather. They deposit their eggs on the skin of cattle, fastening 

 them to the hairs. The eggs are often deposited on the heels above 

 the hoofs, hence the name " heel fly." 



Although the flies are unable to bite, cattle seem to be much afraid 

 of them, and often at their approach make violent efforts to escape, 

 sometimes falling over precipices or becoming mired in water holes 

 in the course of their headlong flight. 



