196 



SCHOOL ENTOMOLOGY 



troublesome enemies. The horn fly resembles a very small 

 house fly, but like the stable fly (page 180), it has piercing 

 mouth-parts which enable it to pierce the skin and suck out 

 the blood, which forms its normal food. When the horn flies 

 assemble in large numbers on the shoulders and elsewhere 

 out of reach of the head or tail, they cause great annoyance, 



FIG. 139. Horn-fly (Hcematobia serrata). Much enlarged. 

 Marlatt, U. S. Dept. Agr.) 



a, egg; b, larva; c, puparium; d, adult in resting position. 



(After 



and have been thought to reduce the milk flow materially 

 and in many cases to cause loss of weight. 



The flies lay their eggs upon freshly dropped cow dung. 

 The eggs hatch in about a day and the little white maggots 

 feed in the dung and become grown in a week or ten days. 

 They then change to pupae just at or below the surface of 

 the ground, and the adult flies emerge a few days later, the 

 whole life cycle requiring about two weeks. 



