DISEASES OF CATTLE 359 



winter and spring, are the larvae of a fly known as the heel fly or 

 warble fly. This fly (Hypoderma 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 car- 

 ried 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 Iarva3 migrate into the esophagus, or gullet, 

 and penetrate into its walls, where they undergo a portion of their 

 development. From the esophagus the larvae migrate through the 

 tissues of the body toward the back, and according to one investi- 

 gator enter the spinal canal, where 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 tke 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 mucous 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 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 coun- 

 try on account of the warble fly is estimated 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. 



Lice. Three species of lice, two of them sucking lice (Hssma- 

 topinus eurysternus, the short-nosed cattle louse, and H. mtuli, the 

 long-nosed cattle louse), commonly known as blue Hoe, and one bit- 

 ing louse (Trichodectes scalaris), commonly known as red louse, 

 affect cattle. 



The blue lice suck the blood of cattle and are more injurious 

 than the red lice. Unless very abundant the latter cause little in- 

 jury. If numerous they irritate and worry their host probably 

 more by their sharp claws than by their bites, as their food seems to 

 consist entirely of particles of hair and dead skin. 



