THE HOUSE-FLY 5 



Our observations indicate that house-flies frequently 

 pass the winter in the pupal stage. We are also of the 

 opinion that adult flies are able to survive the winter. 



The length of time required for a generation of flies to 

 mature varies and will depend upon the temperature, 

 amount of food available, and other factors. For example, 

 in Massachusetts, it may take about fourteen days for 

 a generation of flies to mature, while in the latitude of 

 Washington, D.C., ten days may be sufficient. But 

 it takes the flies several days after they issue to become 

 sexually mature and ready to lay eggs. In Massachu- 

 setts, then, there might be time, 

 during a favorable season, for seven 

 or eight complete generations, while 

 in the latitude of Washington there 

 would be time for ten or twelve Fl - 3 - Puparium of 



,. n i_ ji r house-fly. (X 5.) 



generations. One can hardly realize 

 the enormous numbers that such rapid development is 

 capable of producing. Inside of two months, one female 

 fly can give rise to many millions of progeny. For the 

 purpose of illustration, we will assume that a female fly 

 lays 100 eggs. If these hatch and all the larvae come to 

 maturity, about one-half will probably be males and the 

 other half females. Then at the end of the first genera- 

 tion there will be fifty egg-laying females. At this rate, 

 at the end of the eighth generation there would be pro- 

 duced about 1,875,000,000,000 adults. Of course, in 

 nature, a very large part of these would die and never 

 reach maturity, so that actually one female would prob- 

 ably never produce such an enormous number of 

 individuals. However, under normal conditions tre- 

 mendous numbers are produced. 



