THE ANIMAL PARASITES OF CATTLE. 



523 



they spend a certain period. Finally they appear about January 

 beneath the skin of the back, forming the well-known swellings. 

 The posterior end of the grub is near the small opening in the hide, 

 through which the grub breathes and discharges its excrement, and 

 through which, when its development is complete, it finally escapes. 

 The anterior end of the grub is at the bottom of the tumor, where 

 the mucus collects upon which it feeds. By spring or early summer 

 the grub is full grown and forces its way out of the skin, falling to 



Pig. 11. — The warble fly (Hypoderma lineata) : a, adult female; b, eggs attached to a hair, 

 X 25 ; c, larva as seen in egg ; d, larva from esophagus of an ox ; e, next 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). 



the ground, into which it burrows for a short distance and transforms 

 into the pupal stage. In about a month the mature fly emerges. 



Grubs weaken cattle, cause them to fall off in flesh and milk, and 

 decrease the value of the hide. The beef in the immediate vicinity 

 of a grub becomes slimy and of a greenish color, and is known to the 

 butchers as " licked beef." 



The total loss to this country on account of the warble fly is esti- 

 mated at $35,000,000 to $50,0()0,000 a year. 



