Apr. IS, i9i8 Overwintering of the House Fly 167 



be the usual method of overwintering, at least it proves the possibility 

 in the latitude of Washington. From a mass of pupae collected in a pile 

 of rabbit and guinea-pig manure on February 26, Kisliuk (ij) was suc- 

 cessful in rearing four house flies on March 10 and 12. McDowell and 

 Eastwood (75) record observations of the same kind. Whether the 

 house fiy can overwinter in the lar\^a and pupa stages in more severe 

 climates is still doubtful. C. W. Howard {10) concludes from his ob- 

 servations that — 



the temperature of Minnesota winters is not favorable to the overwintering of the 

 house fly in any except the adult stage and that stage only in places where there is a 

 sufficiently high temperature and where food conditions are favorable. 



SUMMARY AND CONCLUSIONvS. 



The present status of our knowledge of the overwintering habits of the 

 house fly seems to the writer to warrant the following conclusions: 



In the latitude of Washington, D. C, the house fly may overwinter in 

 two ways: (i) By continued breeding in warm places where food and 

 media for deposition are available, and (2) in the larva and pupa stages 

 in or under large manure heaps. 



There is no evidence whatever to show that house flies do or can per- 

 sist as adults from November to April, either outdoors, in protected 

 stables, or in attics or heated buildings. Temperatures of 12° or 15° F. 

 are quickly fatal, and there is every reason to believe that any tempera- 

 ture below freezing is fatal if continued long enough. In heated build- 

 ings their life is not prolonged beyond that of summer at like tempera- 

 ture, nor is there any suspension or retardation of sexual development or 

 activity. 



It is known that house flies continue to emerge from manure heaps as 

 late as the first week in December. Many of these late forms will find 

 their way on mild days to heated buildings, and those which do not are 

 quickly killed. Those that find their way to heated buildings are at- 

 tracted, as in summer, to odors of food and will congregate in kitchens, 

 dining rooms, restaurants, bakeries, animal houses, and the like. If no 

 food is at hand they will quickly perish. When food is available they 

 may continue alive through December and January and even into 

 February, if not destroyed by fungus attacks. But there are neither 

 experiments nor observations to show that they can continue throughout 

 the winter until temperatures are again favorable for outdoor activity 

 and egg laying. If flies find access in the autumn to heated buildings, 

 where both food and media for deposition are available, such as animal 

 houses or restaurants in which sufiicient attention is not given to the 

 disposal of garbage or kitchen wastes, they will continue breeding through- 

 out the winter. In such cases the flies present in March and April are 

 the offspring, not the survivors, of those which found their way to such 

 places the preceding autumn. It is probable that this method of over- 



