216 BOT-FLIES. 
the shape of a shining pupal-case, inside of which the true 
pupa is formed. The insects remain in this shape for about 
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 way 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 larve 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 body, through which the insects obtain the 
necessary air. 
THE RED-TAILED BOT-FLY. 
(Gastrophilus hemorrhoidalis Linn. Ne 
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 
