216 



BOT-FLIES. 



the shape of a shining pupal-case, inside of which the true 

 pupa is formed. Tlie insects remain in this shape for q.bout 

 one month, when the mature winged and sexual flies force 

 their way out of the old shell through an operculum, and en- 

 joy for the first time after a long prison-life the light of day. 

 To enable the flies to force their waj^ out they possess a 

 peculiar bladder-like organ on the front of the head, which, 

 by inflation, swells up and thus can exert considerable pres- 

 sure. It disappears when no longer needed. 



In' fig. 177 are shown the larvae of our three bot-flies, as 

 well as the hooks that enable them to fasten themselves to 

 the mucous lining of the stomach, and the peculiar stigma 

 at the'end of the bod^^ through which the insects obtain the 

 necessary air. 



THE RED-TAILED BOT-FLY. 



( Gastroj)hilus hamiorrhoidalis Linn.). 



This insect was captured upon a horse in St. Anthony 

 Park, hence there is no doubt of its occurrence in Minnesota. 



Fig. 178.— Red-tailed bot-fly. Greatly enlarged. Original. 



The specimen, a male, is illustrated in fig. 178. It is at once 

 distinguished from the above species by the absence of the 

 black spots in the wings. The face is covered with light- 

 colored hairs, the thorax is clothed with olive-gray hairs 



