Apr. 15, 1918 



Overwintering of the House Fly 



161 



throughout the winter only where conditions permitted breeding to 

 continue uninterruptedly. 



Jepson {12) and other observers have proved experimentally that house 

 flies will breed during the winter under the proper conditions. The fore- 

 going studies on the development of the ovaries and the behavior of the 

 flies in the animal house at the Bethesda station, and Kisliuk's observa- 

 tions {13) in the animal house at the Ohio State University and in the 

 Columbus (Ohio) garbage disposal plant, prove that breeding does norm- 

 ally take place in locations where artificial heat, food material, and 

 breeding media are available. Breeding continues all winter in such 

 places, and then on wann days in the spring the flies escape through open 

 windows or doors and take up their usual outdoor activities. This is 

 very probably the explanation of the early appearance of those flies taken 

 in traps on the Bethesda farm in March, 191 7, and also of those found 

 by Dr. Henry Skinner {ij) on March 3, 1913, since in a city there are 

 doubtless many places where breeding occurs throughout the winter. 



RELATION OF TEMPERATURE TO ACTIVITY 



The behavior of house flies at ordinary summer temperatures has been 

 treated fully in the works of L. O. Howard {11), Hewitt {8, 9), Graham- 

 Smith (7), and others. But the following brief notes on the effect of low 

 temperatures on activity have a direct bearing on the question of over- 

 wintering. Observations were made on both laboratory-reared caged 

 flies and wild flies : 



'65° F. .Flies are quite active. 



55° F. .Flies are fairly active. Copulation was noted at 

 this temperature, but no sexual activity has been 

 noted at lower points. 

 52° F. .Flies only slightly active. 



42° F. .Flies move rather weakly when disturbed, but are 

 otherwise inactive. In cages they are usually 

 found on the sides or in comers near the top. 

 40° F. .Flies inactive; crawl feebly when touched. 

 34° F. .Flies inactive; may move legs in weak uncoordi- 

 nated way when touched. 

 F . . One male survived exposure for one week at this 



temperature. {10). 

 F.. Usually no reaction when touched, but they 

 quickly revive when brought into a warm room . 

 F. .Appear to be dead, but most of them revive when 



brought into a warm room. 

 F. .Apparently dead, but in some cage experiments it 

 was found that a considerable percentage re- 

 vived when warmed after exposure to this mini- 

 mum during the preceding night. 

 F .. All dead ; no recovery when taken to a warm room . 

 " None survived exposure for one week. ' ' (70). 

 (^10° F. .AH dead. 



At temperature of, 



30 



29 



25 



