48 THE BOOK OF THE FLY 



exercises a unique capability of walking; the legs are 

 moved three at a time, a front and a hind leg on ont' 

 side advancing simultaneously with the middle leg on 

 the other side ; thus the fly proceeds most securely 

 always poised on three feet, which are so well furnished 

 with pads, claw-like hooks, and hairs, that it can walk 

 over polished glass and can even walk upside-down 

 along comparatively smooth surfaces. 



In comparison with the more heavily constructed 

 wasp, with its four wings, the house-fly, with its two 

 wings, is the more alert and active flier. The wasp is 

 more robust than the fly and w T ill be active in weather 

 too inclement for the latter ; however, some of the 

 frail and slender gnats will brave cold temperatures 

 impossible for the wasp. 



