24 BULLETIN 1369, U. S. DEPARTMENT OF AGRICULTURE 
We ella 
larvee were found four months later, but they were not seen subse- 
quently. 
A few tests have been made to determine if /. lineatum larve will 
develop in guinea pigs. Flies were induced to deposit nearly 100 
eggs on 2 guinea pigs on April 10 and 11, 1923. Eggs from these 
females were shown to be fertile by tests in an incubator, but both 
guinea pigs apparently lost all the eggs before hatching began. 
Several larve of . lineatum from cattle gullets were introduced 
through an incision of the skin on the backs of two guinea pigs. 
Both animals were somewhat stiff and inactive the following day 
and the female soon became very sick. An edematous swelling 
developed on the belly. This finally broke and the animal slowly 
recovered, but there was no evidence of the presence of the larve.. 
The male guinea pig recovered rapidly and a few weeks later 
developed a small lump with a hole through the skin over it, just 
behind the shoulders. This was a typical grub lesion, but the larve 
could not be seen. This disappeared in a few days and no further 
evidence of the infestation was seen. 
As is shown in the discussion of “ injury to man,” infestations of 
humans, especially children, by Hypoderma are not uncommon, 
although it appears that man is not a favorable host. 
ACTIONS OF CATTLE WHEN ATTACKED BY ADULT HYPODERMA 
The reactions of cattle to the attack of these insects is so remark- 
able and so much discussed that a brief statement on this subject 
seems warranted. 
As with the reactions of a host to various other stimuli, we find 
a marked variation in the effect of Hypoderma attack on different 
individuals. This is, however, mainly a matter of degree of violence 
of reaction rather than of kind. As has been mentioned, the fright 
produced by “4. Govis is much more pronounced than that produced 
by H. lineatum, but the latter often causes a wild stampede. 
In the case of both of these species the female has a very flexible 
telescopic ovipositor, in no way fitted for pricking the skin. In fact 
it can scarcely be felt on one’ s hand when it is extended by the fly. 
Convincing evidence of this is also afforded in the fact that flies 
have frequently been seen to approach an animal unnoticed and 
deposit many eggs without any annoyance whatever. 
Careful observations among cattle during heel-fly activity will 
soon convince anyone that it is the attack of the fly which produces 
the fright. The writers agree with Hadwen (36) that this fear is 
produced mainly by the persistent attack of the fly. This is par- 
ticularly true in the case of H. bovis. When the fly first attacks 
cattle at the beginning of the season the reaction against it is usually 
not very violent. The animal kicks or shakes the foot, but the’ | 
immediate return of the enemy alarms the cow and she starts walk 
ing away; being pursued, the fright becomes more pronounced and 
she may run a ~ short distance and begin walking again. The fly 
immediately resumes its attack and then the animal dashes away 
in terror (fig. 5 5, 6), with the insect often at its heels, in the fashion 
of a dog. There is reason to believe that the fear of this insect 
is to some extent instinctive; also that, as the areas of attack become 
