ORDER VII. TWO-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 larg^ 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 arc two-winged in- 

 sects, the females of which deposit their eggs upon the skin 

 of animals, and their larvee 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 GAD-FLY, or LARGE BOT-FLY (Oestrus 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 eggs 

 under the tail of the horse, and that the larvic issuing from 

 them creep through all the intestines until they reach the 

 stomach ; but investigations have shown this not to be the 



