INSECTS AFFECTING MAN AND ANIMALS 389 



astonishing rapidity they are able to consume large quantities 

 of flesh in a remarkably short time. In this way they may be 

 of some importance as scavengers. 



The bot-flies, family Oestrida, are another group of flies that 

 are a great source of annoyance, and often loss, to the stock- 

 man. Rarely, too, the larvae of some of them may infest man. 

 The adult flies look much like small hairy bumble-bees. The 

 mouth- parts are rudimentary so they cannot bite, yet many 

 animals have an instinctive fear of them and will do every- 

 thing that they can to get away from the pests. The common 

 bot-fly of the horse, Gastrophilus equi, attaches its eggs to the 



FIG. 176. Horse bot-fly, Gastrophilus equi. (Two and one-half times 

 natural size.) 



hair of the legs or some other part of the body of the animal. 

 The horse licks off the eggs into its mouth. The eggs hatch 

 just before or after they are licked off and the larvae develop 

 in the alimentary canal of their host. Sometimes the walls of the 

 stomach may be almost covered with the larvae that have at- 

 tached themselves there. This of course seriously interferes 

 with the function of this organ. When full grown, the larvae 

 pass from the horse with the droppings, and complete their 

 transformations in the ground. There are two other species of 

 bot-flies attacking the horses. These have habits similar, in 

 most respects, to the species just described. 



