; 
Germany, Switzerland, Denmark, Holland, and the British Isles, 
THE CATTLE GRUBS OR OX WARBLES 111 
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, 47. bovis De Geer is essen- 
tially a northern form as shown by its distribution, both in the 
- United States and in Europe. In the United States 17. lineatum is 
much more widely distributed than //. 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. ZH. bovis, on the other hand, appears to 
_ have been introduced into the United States from Kurope rather re- 
cently. 
Injury to cattle by these insects comes from (1) the annoyance 
caused by the flies during egg deposition and (2) the irritation pro- 
_ duced by the larve within the bodies of the hosts. The yearly loss 
to the hide, tanning, and leather industries of the United States 
caused by these grubs 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 1. bovis and H. lineatum. 
The American bison is also a host of H. lineatum. Although horses 
_are attacked, in nature very few larve 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 larve 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 larve 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 egg 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 larve reach the 
subdermal tissues or on the time of their appearance. Larve enter- 
ing the skin of an animal on the legs may go to the submucous layers 
of the gullet, as may also larve removed from the gullets and intro- 
duced by incision under the skin on the leg of a bovine. 
H. lineatum prefers the heels as points for the attachment of its 
eggs, but eggs may be found on many other parts of the host. /H. 
bovis oviposits on the legs, but more eggs are laid on the thighs and 
about the rumps of the cattle than with HZ. lineatum. 
_ #. lineatum attaches its eggs in rows on the hairs; H. bovis de- 
posits its eggs singly. 
_ The usual incubation period for HZ. lineatum is from 3 to 6 days; 
for H. bovis, about 3 days. 
___ After penetrating the skin the larve apparently work upward in 
_ the connective tissue and begin to appear in the chest and abdominal 
_ cavity about two months after penetration. Although many larve 
_ enter the connective tissue of the gullet it appears that many may 
_never enter that organ. This is particularly true of H. bovis, as 
_ only one larva of this species was found among 1,140 specimens re- 
moved from 563 gullets in regions where this species abounds. Of 
3,022 larve removed from 1,137 gullets, the majority were in the 
second stage, only a few being in the third. 
