Apr. 15, iQis Overwintering of the House Fly 157 



warmth from the heater and the odor of decaying cabbage proved very 

 attractive to house flies, and large numbers congregated here early in 

 the fall and were present in considerable numbers throughout the winter. 

 That the house flies present here during March and the early part of 

 April, 1 917, were not the sur\dvors but rather the offspring of those 

 which had congregated here in the fall of 191 6 is quite clearly indicated 

 from the following observations : 



It was noted that large numbers of these flies were carried off during 

 December and early January by the attacks of a fungus, doubtless 

 Empusa muscae. For example, on January 4, on one of the supporting 

 posts near the heater, 68 victims of the fungus were counted. These 

 were swept off, and six days later about 30 fresh victims were counted. 

 Shortly after this date all the woodwork of the interior of the building 

 was painted and no more deaths from fungus were noted, but dead flies 

 were occasionally found on the floor below windows or between the 

 windows and screens. In spite of these deaths there was no very notice- 

 able falling off in the number of active adults which frequented the pile 

 of cabbages. It was evident that breeding was taking place and that 

 freshly emerged flies were steadily appearing to take the place of those 

 killed by natural causes. 



The breeding places were not definitely located. The cages for rabbits 

 and guinea pigs were kept in excellent condition. All excrement, soiled 

 litter, and vraste food were removed from the cages every day, or at 

 least every other day, and hauled away from the building. Floors under 

 and around the cages were swept clean. The only possible place for the 

 development of the lar\'ae seemed to be in the decaying portions of the 

 cabbage. No lot of cabbage remained on the floor near the heater more 

 than four or five days before it was used for feeding. It is possible, 

 however, that flies may have oviposited on some decaying portion of the 

 cabbage, and the issuing lars^ae may have had three or four days devel- 

 opment before being disturbed. Then, some may have been transferred 

 with the food to the animal cages, where they possibly would have had 

 time to complete their growth and to pupate in some obscure comer of 

 the cage or in clean litter, and thus escape the cleaning process. The 

 warmth near the heater and the warmth in the cages from the bodies of 

 the animals would be sufficient to carry through development to pupa- 

 tion at about the normal rate. A study of the adults showed conclu- 

 sively, however, that breeding was taking place and that freshly emerged 

 flies were appearing from time to time. 



Deposition of eggs was easily induced when a suitable medium was 

 exposed. Thus, on December 13 a i -gallon, v/ide-mouthed glass jar was 

 half filled with moistened bran and exposed on a low support near the 

 pile of cabbages. The warmth soon produced an active fermentation 

 and eggs were obtained on December 15. Again, similar depositions 

 were obtained on December 22, December 28, January 6, and other sub- 



