THE HOUSE FLY, 7 



burrow into tlie soil beneath, or they may crawl considerable dis- 

 tances away from the pile to pupate in the ground or in loose material 

 under the edges of stones, boards, etc. 



The pupas (fig, 11), or "sleepers," are more or less barrel shaped 

 and dark brown in color. In midsummer this stage lasts from three 

 to ten days, four to five days being the usual duration. The pupa 

 stage is easily affected by temperature changes and may be prolonged 

 during hibernation for as long as four or five months. Numerous 

 rearing experiments in various parts of the country have shown that 

 the shortest time between the deposition of eggs and the emergence 

 of the adult fly is eight days, and 10 and 12 day records were very 

 common. 



The adult fly, upon emergmg from the puparimn, works its way 

 upward through the soil or manure and upon reaching the air it 

 crawls about while its wings ex- 

 pand and the body hardens and 

 assumes its normal coloration. In 

 a very few days the female is 

 ready to deposit eggs. In recent 

 experiments it was found that the 

 time between the emergence of the 

 adults and the first deposition of 

 eggs is considerably shorter than 

 previously was thought to be the 

 case. Only three or four days are 

 necessary in midsummer for the 

 female to reach sexual maturity. 

 As in the case of other periods of 



its life history, so the preoviposi- Fig. 9.-Eggs of the hmise ny. Hfehly magnified. 

 , T . , 1 ., (Newstead.) 



tion period is prolonged consider- 

 ably by the lower temperatures of spring and autumn. In mid- 

 summer, with a developmental period of from 8 to 10 days from 

 egg to adult, and a preoviposition period of from 3 to 4 days, a 

 new generation would be started every 11 to 14 days. Thus the 

 climate of the District of Columbia allows abundance of time for 

 the development of 10 to 12 generations every summer. 



HOW THE HOUSE FLY PASSES THE WINTER. 



The prevailmg opinion that the house fly lives through the winter 

 as an adult, hiding in cracks and crevices of buildmgs, etc., appears 

 to be erroneous. Under outdoor conditions house flies are killed 

 during the first really cold nights, that is, when the temperature 

 falls to about 15° or 10° F. In rooms and similar places protected 

 from winds and partially heated during the winter flies have been 

 kept alive in cages for long periods; but they never lived through 



