500 DISEASES OF CATTLE. 



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

 {Hyvoderma lineata) is about one-half inch long, very hairy, and 

 somewhat resembles a small black bee in appearance. The flies 

 appear early in the 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. Many eggs are 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 apparently are sometimes stampeded by them. Either 

 the eggs or the tiny maggots hatching from them are carried into the 

 mouth by the cattle licking themselves. In the former event the 

 eggs hatch in the mouth or in the paunch. In either case the maggots 

 or larvse migrate into the esophagus, or gullet, and penetrate into its 

 walls, where they undergo a portion of their development. From the 

 esophagus the larvse migrate through the tissues of the body toward 

 the back, and according to one investigator enter the spinal canal, 

 where they spend a certain period. Finally they appear about Jan- 

 uary 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 

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

 into the pupal stage. In about a month the mature fty 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 kuown 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 $50,000,000 a year. 



Treatment for warbles. — During the winter press out the grubs and 

 destroy them, using a knife if necessary to enlarge the opening; or 

 inject a few drops of kerosene into the swelling through the opening, 

 using a machinist's oil can for the purpose. To keep off the flies 

 during the summer, the cattle may be frequently treated with one of 

 the fly repellants already mentioned (p. 495). 



LICE.® 



Three species of lice, two of them sucking lice (Hcematopinus ev/ry- 

 sternus, the short-nosed cattle louse, and H. vituli, the long-nosed 

 cattle louse), commonly known as blue lice, and one biting louse 

 (Trichodectes scalaris), commonly known as red louse, affect cattle. 



a For further information see Bulletin 5, new series, Bureau of Entomology. 



