Dec, 1916.] Gastrophilus h^morrhoidalis Linn^us. 255 



consist of chitinous bands. On the stalked portion these "bands" are 

 widest and appear like a spiral, the margin farthest from the tip 

 having the greater circumference. This gives the stalk the general 

 appearance of a screw and the structure is patently adapted to hold 

 the egg in the skin after insertion. Fig. 2 is an outline sketch to 

 show the micropyle and the cap, the latter probably permitting the 

 escape of the larva. Horses, immediately upon being " struck," 

 often rub their noses and lips violently on the ground, posts, or other 

 handy object. This action may loosen the cap, but apparently is not 

 effective in dislodging the eggs. 



Both males and females were seen in the vicinity of horses, the 

 latter greatly predominating. There is some reason to believe that 

 copulation takes place on the wing in the vicinity of horses, but 

 sufficient observations were not made to feel certain on this point. 



As noted at Powderville, Montana, the nose fly first appears 

 about the middle of Tune and stays until the middle of July. This 

 same period was that of greatest abundance for G. eqiii Fabricius 

 and G. nasalis Linnaeus. The latter two species were afterwards 

 seen occasionally until shortly after the first of September, when the 

 field work was brought to a close. During the time when the nose 

 fly is abundant horses are often irritated even by the buzzing of 

 blow flies and others that make a similar noise. 



The above observations are interesting in view of the fact that it 

 has been previously supposed that the eggs were fastened to hairs 

 about the mouth, or according to one writer, in the vicinity of the 

 anus. The fact that larvae may be found attached to the rectum may 

 have been responsible for the latter idea. Several lots of larvae 

 detached from the rectum and reared to the adult, proved to be 

 Gastrophilus hccniorrhoidalis. 



The writer acknowledges his indebtedness to Mr. R. W. Wells, 

 who assisted him in most of the observations made. 



