212 BOT-FLIES. 



that begins at the posterior end and progresses toward the 

 head enables them in a few minutes to free themselves, Avhich 

 they usually do in the morning hours. Upon the ground 

 they creep about until they meet some obstruction, when 

 they burrow from one to two inches below the surface, and 

 remain as in the gastrophihis species." 



The bot-flies which infest domesticated animals have 

 been transported with their hosts to nearly all parts of the 

 globe; others are found in wild animals. These flies can be 

 divided into three groups, according to their mode of exis- 

 tence: 1, Gastric, or grubs that live in the stomach of their 

 host; for example the Bot-flies of the horse (fig. 175). 2, 

 Ceplicdlc, or grubs that live in the nostrils and frontal sinuses 

 of their host; for example, the Sheep Gad-fly (fig. 181). 3, 

 Cutaneom, or grubs that cause and live in tumors just below 

 the skin; for example the Ox Warble-fly (fig. 183). 



The Bot-flies belonging to the genus Gastrophilus are 

 well-known parasitic insects, most of w^hich live in their 

 larval stages in the stomach of horses. At least three species 

 are found in Minnesota, but as all possess a very similar life- 

 history only that of the best known species will be given. 



THE COMMON BOT-FLY. 



( (histrapldliis equi Fab.). 



The illustration (fig. 175) shoAvs this wooly insect which 

 resembles in many ways a common honey-bee. It has a 

 fawn-colored face, which is covered with a silky down; the 

 thorax is covered -with reddish hairs, and has, very fre- 

 quently, a black transverse band. The abdomen is yellow- 

 ish or reddish-brown with irregular darker spots; that of 

 the female ends in a long ovipositor bent around, as seen to 

 the left of the figure, while that of the male is obtuse. The 

 wings in this species are transparent, and have near their 

 middle a transverse smoky bar and two spots of the same 

 color near the tip. The fly measures from 12 to 14mm. 



During the whole summer these insects can be found, but 

 principally during July and August, when the females are 

 most active during the warmer part of the day; they 

 may be seen buzzing about horses, asses and mules, balanc- 



