42 



PARASITES OF THE DOMESTIC ANIMALS 



this species of clustering about the base of the horn, though this only 

 occurs when they are quite abundant. Their purpose in collecting here 

 seems to be for rest in a location where they are not liable to be dis- 

 turbed. There is a somewhat prevalent belief that the flies damage the 

 horn by eating into it, depositing eggs, and developing maggots which 

 may penetrate to deeper structures, etc. This is a popular error for 

 which there is no foundation, for, beyond "fly specking," it has not been 

 observed that the flies do any injury to the horn. 



Field study will show that this insect assumes two characteristic posi- 

 tions. In the resting position, as they are found when upon the horns. 



Fig. 23. — Lyperosia irritans: a, egg; b, larva; c, puparium; d, adult in biting 

 position — all enlarged (after Osborn, from Riley and Howard, Bui. No. 5, Bu- 

 reau of Entomology, Dept. of Agr.). 



the wings are held nearly flat down the back, overlapping at their bases 

 and moderately diverging at their tips. The proboscis is extended for- 

 ward, and the legs are not widely spread. When active and feeding, on 

 the other hand, the wdngs are slightly elevated and held almost at right 

 angles to the body, while the legs are spread. The proboscis is nearly 

 perpendicular in position, and penetrates the skin of the animal at- 

 tacked. To secure this position it works its way to the skin, and is 

 usually observed more or less covered by the hairs. In damp, rainy 

 weather they may be noticed as particularly abundant beneath the 

 hairs of the ventral surface of the body. 



Effect. — Horn flies appear early in May and become most abundant 

 in July and August. With the coming of cold weather they disappear, 



