32 BULLETIN" 597, U. S. DEPARTMENT OF AGRICULTURE. 



GASTROPHILUS INTESTINALIS (DeGeer). 



SYNONYMY. 



Oestrus bovis Linnaeus. 1761. 

 Oestrus intestinalis De Geer, 1776. 

 Oestrus equi Clark, 1797. 

 Gastrophilus equi Leach. 1817. 

 Gastwis equi Meigen, 1824. 

 Oestrus gastricus major Schwab, 1840. 



OPPOSITIONS AND LONGEVITY. 



The universal distribution of the common bot-fly, the familiarity 

 of innumerable persons with its oviposition habits, and the numerous 

 publications dealing more particularly with ovipositions and ingress 

 of the larvse into the host since Bracy Clark (1797), leave little to be 

 desired. It is probable that there is no other insect whose eggs come 

 so directly under the observation of farmers as does the common bot- 

 fly. The common names of this Gastrophilus vary with the locality, 

 but farmers are usually aware of the fact that this insect produces the 

 bots in horses. 



Some authors contend that the eggs are deposited upon those 

 places most accessible to the horse's mouth, while others hold that 

 the fly will deposit upon any portion where it is not disturbed. 

 It has always been observed that these flies give preference to the 

 forelegs, and. after these have become well covered with eggs, depo- 

 sitions occur at other points where the fly is not disturbed by the 

 horse's tail. Very few eggs are deposited upon the hind legs or upon 

 the backs of the animals, but when adult flies are in numbers the 

 mane may become heavily infested, especially near the shoulder. 

 Large numbers of eggs may be found upon the sides of the animals, 

 and these are concentrated at points accessible to the mouth, as in 

 cases of depositions upon the inside of the forelegs. It seems that 

 the fly oviposits on the forelegs instinctively, and, after the legs 

 become heavily infested, adults may be observed to deposit one or 

 two eggs on them and then seek other portions of the body. At times 

 two or more eggs may be found upon a single hair on the inside of the 

 forelegs, but seldom has this been noted upon other portions. How- 

 ever, the length of the mane often permits adults to deposit large 

 numbers upon a single hair. TTith the exception of the forelegs, the 

 sides below and to the rear of the shoulder blades probably harbor 

 most eggs. 



The longevity of 11 reared adults in 9 tests, in which the flies 

 were kept under conditions similar to those employed in rearing G. 

 haemorrhoidalis varied from 7 to 21 days. The longer periods oc- 

 curred during early fall, when lower temperatures were experienced. 

 These adults, like those of other species of Gastrophilus. were never 



