FAMILY MUSCID^ 



277 



deposit their eggs upon the spider, the larva feeding upon 

 the food intended for the wasp larva or possibly upon the 

 wasp larva itself. 



The typical Muscid flies {MuscidoB), house fly, blow fly 

 screw-worm fly, all live in organic matter in a state of decay, 

 and all of them show very rapid rate of development, the 

 larvae acquiring their growth in a few days' time, though 

 longer time is usually passed in the pupa stage. The adults 

 may live for a long time. House flies, for example, conceal 

 themselves about houses and survive the winter, possibly 

 also as pupse, and deposit eggs which start the summer 



Fig. 222. — Common house fly (Musca domestica) : puparium at left; 

 adult next; larva and enlarged parts at right. All enlarged. (After Howard, 

 Div. Ent., U. S. Dept. Ag.) 



generations which follow each other with a great deal of 

 rapidity. Twelve to fifteen days is all that is required for 

 the complete cycle of many of the species. They are scaven- 

 gers and in this may be looked upon as beneficial. They 

 present also certain dangerous aspects as carriers of disease, 

 especially typhoid, and deserve all the opposition they are 

 receiving. 



The screw-worm fly deposits eggs occasionally in the 

 nostrils of individuals, and in the case of wounds of animals 

 the larvae work into the living tissue. It causes losses in 

 cattle industry in the South. 



