PARASITES OF ANIMALS. 29 



horses. They change to pupae beneath the manure, and the 

 flies appear from June to September. It also infests the ass 

 and mule, and some authors say that it lives even in cattle. 



The Gaslrophilus pecorum is densely covered with yellow 

 hairs, with a band of black hairs on the thorax behind the 

 suture, in the male. The female is yellowish brown, the 

 abdomen black, with yellowish hairs at its base, as well as 

 on the thorax. The wings are grayish or light brownish, 

 clouded with yellowish brown. The larvae are similar to 

 those of the more common G-. equi, and have similar habits. 

 The flies appear at the same time. 



The Gastrophilus hcemorrhoidalis, or red-tailed bot-fly, is 

 a small species, easily distinguished by the bright orange-red 

 tip of the abdomen. The thorax above is olive-gray and hairy, 

 with a black band behind the suture. The base of the abdo- 

 men is whitish and the middle blackish, in strange contrast- 

 with the orange-red of the end. The larvae have the same 

 habits and are found in the same situations with those of 

 the common bot-fly, which they much resemble, except that 

 they are whiter and smaller, their length not exceeding one- 

 half or five-eighths of an inch. They change to pupae within 

 two days after leaving the horse, and the pupae are deep red. 

 They remain in the pupa state about two months, and the flies 

 appear from the last of June till the cool weather of autumn. 

 In depositing the eggs, the female fly differs in habit from 

 the common bot-fly, for she selects the lips and nose of the 

 horse as the most suitable place for this purpose. In deposit- 

 ing her eggs she therefore causes the horse much trouble and 

 uneasiness. Mr. Clark described the operation as follows : 

 " At the sight of this fly the horse appears much agitated, 

 and moves his head backwards and forwards in the air to 

 baulk its touch and prevent its darting on the lips ; but the 

 fly, waiting for a favorable opportunity, continues to repeat 

 the operation from time to time ; till at length, finding this 

 mode of defence insufficient, the enraged animal endeavors 

 to avoid it by galloping away to a distant part of the field. If 

 it still continues to follow and tease him, his last resource is 

 in the water, where the (Estrus is never observed to follow 



