78 INSECTS AFFECTING DOMESTIC ANIMALS. 
no definite statistics can be given for the losses incurred. It is prob- 
ably safe to say that nine-tenths of all colts and horses that are pas- 
tured during summer, and a smaller proportion of driving and work 
horses, become infested with bots each year. Aside from the injuries 
inflicted by the larve, we must consider the excitement produced by 
the flies when depositing the eggs as a source of loss, and this in many 
cases is by no means insignificant. 
LIFE HISTORY AND HABITS. 
Adults of this species are about three-fourths of an inch in length, 
the wings are transparent with dark spots, those near the center form- 
ing an irregular, transverse band. The body is very hairy, the head 
brown with whitish front, thorax brown, abdomen brown with three 
rows of blackish spots, which are subject to considerable variations. 
In the females the segments are often almost entirely brown with sim- 
ply a marginal series of yellowish spots, while in males the abdomen 
may be almost entirely yellow or very light brown, with brown or dark 
Fia. 37.—Gastrophilus equi: a, egg—enlarged; b, egg—natural size; c, young larva; d, young larva— 
much enlarged, showing spiny armature; e, oral hooks; jf, body spines; g, full-grown larva—twice 
natural size; h, adult female (original). 
spots very distinct. The males are rarely seen, for while it is one of 
the most common occurrences to witness the female around the horses 
depositing their eggs, the males evidently hold aloof. They are readily 
distinguished by the form of the abdomen, which lacks the two tubular 
segments at the end, and is provided on the under side of the last seg- 
ment with a pair of dark-brown or black hooks, or clasping organs. 
Otherwise, except the color of the abdomen, already mentioned, they 
resemble very closely the females. The eggs (fig. 37, a and b) are light 
yellow in color and will be found attached to the hairs of the shoulders, 
