THE HOUSE FLY AND DISEASE 



8l 



manure piles contain an enormous number of maggots; an 

 average of fifteen hundred to every pound of manure has been 

 recorded. 



Enemies of House Flies. In the late autumn there is a 

 notable decrease in the number of flies and in winter none are 

 present except in warm situations. The question has often 

 been asked, What becomes of the flies in the winter, and where 

 do the flies come from in the spring? House flies, like all other 

 animals, have many enemies. Numerous birds, such as vireos 

 and phcebes, are known to catch them; predaceous insects, like 



FIG. 51 b. The house fly. 

 A, larva or maggot ; B, puparium ; C, adult. (After Howard.) 



the wasps, destroy many of them; toads, frogs, and lizards 

 devour them whenever they get a chance; and the house centi- 

 pede (Fig. 52, A) is a constant enemy. These animals are all 

 attacking the flies during the summer. As autumn approaches 

 a fungous plant (Empusa muscce) kills enormous numbers of 

 them; it is, in fact, their worst enemy. This plant is responsible 

 for the death of the flies that are often found attached to window- 

 panes and surrounded by a grayish ring which consists of the 

 seedlike reproductive bodies of the plant (Fig. 52, B). A large 

 proportion of the flies die a natural death, but the vigorous 

 young crawl into crevices, where they pass the winter in a quies- 



