DIPTERA 



865 



as bots. These insects constitute the genus Gastrophilus, three species 

 of which are now well established in the United States and Canada. 

 In the adult flies the oral opening is small and the proboscis vestigial. 

 The members of this genus can be distinguished from those of the 

 following family by the venation of the wings ; the most striking fea- 

 ture of which is that vein Ml +2 extends in a nearly straight line towards 

 the margin of the wing (Fig. 1115). 



Fig. 1 1 15. — -Wing of Gastrophilus. 



The genus Gastrophilus has been commonly included in the family 

 CEstridccbut it is now believed to represent a distinct line of develop- 

 ment. The three species that are established in this country are the 

 following. 



The common bot-fly or the stomach bot, Gastrophilus intestindlis. 

 — The adult fly closely resembles the honey-bee in form except that 

 the female (Fig. 11 16) has the end of the abdomen 

 elongate and bent forward under the body. The wings 

 are transparent with dark spots, those near the center 

 form an irregular, transverse band. This fly is most 

 often seen flying about horses, which have an instinctive 

 fear of it. The eggs are laid on different parts of the 

 host, but preferabh^ on the long hairs investing the 

 inside of the forelegs. The eggs rarely hatch when left 

 untouched; but the horse by scratching the forelegs 

 with the teeth removes the small cap of the egg-shell and inadvert- 

 ently takes the larva into its mouth. The larvae thus taken into the 

 mouth are carried with the food or water to the stomach. When the 

 larvae reach the stomach they fasten themselves to the inner coat of 

 it, and remain there until full-grown. Then they pass from the 

 animal with the dung, and crawl into some protected place, where 

 they transform within a puparium. The adult fly measures about 

 18 mm. in length. This species is found throughout the United 

 States and Canada where horses are present. It has been commonly 

 known as Gastrophilus equi, but intestinalis is the older specific name. 



Fig. 1 1 16. 



