ORDER VII.—TWO0-WINGED INSECTS, OR FLIES. 295 
Flies are of very little use to man, and are generally 
deemed injurious insects, as many of them are able indirect- 
ly to kill even large quadrupeds; most of them vex us by 
their impudence, and torment man and beast by their stings 
and blood-sucking ; while, in the maggot state, they even 
dwell in the skin on frontal cavities, or even in the entrails 
of some animals. So many dogs and other animals perish. 
The number of genera of this order is immense, and far 
surpasses that of the lepidoptera. The most conspicuous 
of those found in the United States are the following: 
The Gad-fly. 
These resemble bumble-bees, and are sometimes known 
under the name of Bot-bees. These are two-winged in- 
sects, the females of which deposit their eggs upon the skin 
of animals, and their larve enter the body, and dwell either 
under the skin, or in the nose, or in the entrails. Of these 
there are several species. 
The Horse Gap-rry, or LarcE Bor-Frriy (@strus equi), 
has spotted wings, and a body covered with yellow hair. 
This is one of the principal flies whose young sometimes 
cause the death of a horse. “The horse, which, among the 
animals useful to man, occupies the first rank, seems not to 
have been created for man alone; but even an insignificant 
fly usurps dominion over him, appropriates him to his own 
use as an article of food; so that while the horse is simply 
useful to man, he is really necessary to the existence of 
these insects, who can only live and develop in his stomach 
and intestines. The stomach of a horse is sometimes paved 
with these larvae, or bots, as a street is paved with stones, 
and this, too, without the animal seeming to suffer by it. 
Formerly it was believed that this gad-fly deposits her eges 
under the tail of the horse, and that the larve issuing from 
them creep through all the intestines until they reach the 
stomach; but investigations have shown this not to be the 
