8 



FARMERS BULLETIN 851. 



the entire winter. In several cases longevity records of from 52 

 to 54 days were obtained. In other experiments one record of 70 

 days and another of 91 days was obtained. The average tem- 

 perature of these experiments varied from 44 to 57 F. The 

 conditions of these experiments seemed to have been most favor- 

 able, but flies normally do not seek such places. No uncaged 

 house flies were found during three seasons' observations in unheated 

 and only partially heated attics, stables, unused rooms, etc., where 

 favorable temperature conditions prevailed. The common occur- 

 rence in such places of the cluster fly and a few other species, which 

 may be easily mistaken for the house fly, is responsible for the pre- 

 vailing belief as to the way the house fly overwinters. There is there- 

 fore no reliable evidence whatever that adult house flies emerging 

 during October and November pass the winter and are able to de- 

 posit their eggs the following spring, although they may continue 

 active in heated buildings until nearly the end of January. On the 

 other hand, there is evidence that house flies pass the winter as larvse 

 and pupae, and that they sometimes breed continuously throughout 

 the winter. In experiments at both Dallas, Tex., and Bethesda, 

 Md., house flies have been found emerging during April from heavily 

 infested manure heaps which had been set out and covered with 

 cages during the preceding autumn, this proving that it is possible 

 for them to overwinter as larvse and pupaB in manure heaps or in the 

 soil beneath such heaps. 



FIG. 10. Larvae, or maggots, of the house fly. About natural size. (Xewstead.) 



