﻿THE CATTLE GRUBS OR OX WARBLES 111 



Germany, Switzerland, Denmark, Holland, and the British Isles, 

 and probably occur throughout the remainder of Europe. They 

 have been reported also from North Africa, western India, Mongolia, 

 and parts of Japan. Of the two species, H. hovis De Geer is essen- 

 tiall}^ a northern form as shown by its distribution, both in the 

 United States and in Europe. In the United States H. Uneatmrh is 

 much more widely distributed than II. bovis, has been known for 

 many more years, and has been bred from the native bison; possibly, 

 therefore, it may be an American species, although now occurring in 

 other parts of the world. II. horns, on the other hand, appears to 

 have been introduced into the United States from Europe rather re- 

 cently. 



Injury to cattle by these insects comes from (1) the annoyance 

 caused by the flies during Qgg deposition and (2) the irritation pro- 

 duced b}^ the larvae within the bodies of the hosts. The yearly loss 

 to the hide, tanning, and leather industries of the United States 

 caused by these grufe is estimated at $5,000,000 and the yearly losses 

 to the people of the United States at $50,000,000. 



Cattle are the normal hosts for both H. hovis and H. lineatwrn. 

 The American bison is also a host of H. lineatunh. Although horses 

 are attacked, in nature very few larvse ever reach maturity in them. 

 Goats may occasionally serve as hosts but in experiments with them, 

 as also with sheep, dogs, rabbits, and guinea pigs, no larvse were 

 successfully reared. Several cases are known of the infestation of 

 man by these parasites. 



In several series of experiments with cattle controlled by muzzles 

 and cages it was determined that the larvse upon hatching from the 

 eggs penetrate through the skin at the points where the eggs are 

 laid and do not enter the host by the mouth, either in the Qgg or 

 larval stage. 



It was found that the place where the eggs are laid on the host 

 has no apparent effect either on the place where the larvae reach the 

 subdermal tissues or on the time of their appearance. Larvae enter- 

 ing the skin of an animal on the legs may go to the submucous layers 

 of the gullet, as may also larvae removed from the gullets and intro- 

 duced by incision under the skin on the leg of a bovine. 



//. linsfitiim piefers the heels as points for the attachment of its 

 eggs, but eggs may lie found on many other parts of the host. II. 

 hovis oviposits on the legs, but more eggs are laid on the thighs and 

 about the rumps of the cattle than with II. lineatum. 



H. lineatum attaches its eggs in rows on the hairs; II. hovis de- 

 posits its eggs singly. 



The usual incubation period for II. Imeatutn is from 3 to 6 days; 

 for II. hovKH., about 3 days. 



After penetrating the skin the larvae apparently work upward in 

 the connective tissue and begin to appear in the chest and abdominal 

 cavity aix^ut two months after penetration. Although many larvae 

 enter the conn(;ctive tissue of the gullet it a|)pearH that many may 

 never enter thai organ. This is particularly true of //. hoiy'is, as 

 only one larva of this species was found among 1,140 specimens re- 

 moved from 563 gullets in regions whei-e this species abounds. Of 

 ;'>,522 larva) removed from 1,137 gullets, the majority were in the 

 second stage, only a few being in the third. 



