DIPTERS: FLIES. 



155 



two small knobbed threads, called balancers. Mosqui- 

 toes have a long bill composed of bristles sharper than 

 the sharpest needles, with which they pierce the flesh 

 of men and animals, and secure the blood upon which 

 they so much delight to feed. The female lays her 



Fig. 287. Horse-Fly. 



Fig. 288. Bee-Fly. 



Fig. 289. Asilus-Fly. 



Fig. 290. Bot-Fly. 



eggs on the surface of the water, and the larvae may 

 be seen in great numbers, throughout the summer, in 

 all stagnant pools. They are very lively, and move 

 with a wriggling motion. They rest with the head 

 downward, and with the hind extremity of the body 

 through which they breathe at the surface of the 

 water. At length they shed their skins and enter upon 

 the pupa state, in which they live at the surface of the 

 water, and breathe through two tubes on the thorax. 

 In a few days the skin splits on the back, the winged 

 insect appears, and, after resting awhile on its empty 

 skin as it floats upon the water, spreads its wings, and, 

 humming its war-note, flies away in search of a vic- 

 tim whom it may pierce, for blood. 



