THE FLY 



83 



The black-flies are familiar pests in the forests of our North- 

 ern country. The females, which alone suck blood, occur in 

 such numbers and are so active that they render certain places 



Fig. SG. — Tahatuis lineola, whitn- 

 lined horse-fly. X 1.2. Photo, by 

 W. H. C. P. 



Pig. 87. 

 fly. ;■ 



— ChrysojK, banded horse- 

 1..5. Photo, by W.H.C.P. 



almost uninhabitable to man. Their bite often produces 

 •\vide-spreading and painful inflammation, accompanied by 

 swelhng (Fig. 88). The larvse are aquatic. The Southern 

 black-flj' or " l)uffalo-gnat " sometimes 

 causes the death of domestic animals. 



The gall-gnats are minute flies which 

 lay eggs on plants. The larvae make their 

 way into the plant tissue, and cause the 

 further development of the tissue to be 

 abnormal, so that excrescences or galls are F'g- SS. — Simuiium, 

 produced. The galls are formerl only in i a r g e d. Fro m 

 growing tissue such as the tips of branches, Paekai-d. 

 buds of flowers or gromng leaves, and are less striking on the 

 whole than the galls of Hemijitera (Tig. 89). A certain kind 

 of gall-fly, called Hessian-fly (Fig. 90), is extremely injurious 

 to wheat because it infests wheat seedlings and so weakens 

 them that they produce no grain. Other minute gnats or 

 midges are destructive to clover in the United States, either 



