368 



GENERAL BIOLOGY 



already described as killing grasshoppers, and Syrphus flies ( ) 



feed on insects and are therefore of value to man, but nearly all others 

 should be exterminated. Over ninety per cent of the flies found in and 

 about homes are the regular typhoid flies. When it is remembered that 

 the feet of these are furnished with claws for climbing over rough sur- 

 faces as well as with two pads, the pulvilli, covered with sticky, tubular 

 hairs by which the animal can attach itself to ceilings and glass surfaces, 

 one can understand the excellent summing up of what this means that 

 "No more effective mechanisms for collecting dust could be designed 



Fig. 240. 



The Friend of Farmers. Red-tailed tachina-fly (Winthemia 4-pustulata.) a., 

 natural size ; b., much enlarged ; c., army worm on which fly has laid eggs, natural 

 size; d., same, much enlarged. (After S. Singerland.) 



than a fly's feet and proboscis (Fig. 216), a combination of six feather 

 dusters and thirteen damp sponges. While the constant 'cleaning' move- 

 ments of flies are clearly designed to rub off and scatter the adhering 

 germs everywhere they go." 



There are "little house flies" (Fannia canicularis) which probably 

 most people believe grow into the regular house fly. Their breeding 

 habits and feeding places are quite similar to the house fly, but, as flies 

 hatch in the adult form they do not grow after once becoming flies. 



Other flies such as bluebottles, greenbottles, and flesh flies or blow- 

 flies are also found about the home and frequently lay their eggs on meat. 

 These flies are scavengers. 



In the South there is the screw-worm fly (Chrysomyia macellaria) 

 which deposits its eggs on wounds, for the maggots of this species feed 

 on living flesh. It is these flies also which are likely to lay their eggs 

 in the nostrils and ears of children or even of adults as they sleep out of 



