156 Journal of Agricultural Research voi. xiii. No. 3 



By restricting obsen/ations to certain selected places and by continuing 

 them throughout the entire season the writer has been able to collect 

 data which, it is believed, offer an explanation of the presence of flies 

 during the winter months and of their ultimate fate. The following 

 paragraphs bear on this point. 



Some observ^ations were made at a boarding house near Washington 

 during the winter of 191 5-1 6. There seemed to be complete indifference 

 on the part of the occupants to the presence of flies, and the writer, 

 in order to make some observations on these flies under natural conditions, 

 was careful not to arouse any enthusiasm for fly killing. House flies 

 were present in kitchen and dining room, and occasionally in bedrooms, 

 throughout the fall and early mnter. Their numbers gradually decreased 

 as winter set in, but a few stragglers were noted and watched well into 

 January. The last of them (two males) were noted in bedrooms on 

 January 31 . None were again seen in this house until the followdng May, 

 some time after they had first appeared outdoors. 



At the Bethesda station a small building is used daily for baking a 

 coarse bread from meat scraps and com meal to be fed to dogs. Tem- 

 peratures were always high during the day, but the fires were allowed to 

 go out during the night, and at such times the temperature often fell 

 below freezing. House flies were present in large numbers during the 

 fall, Empusa muscae carried off large numbers of them, but, in spite 

 of this, some persisted during December and well on into January. There 

 was a gradual and steady decrease and the last ones were observed on 

 January 27, after which none were again seen here until the following 

 May. 



In both the above cases the flies had free access to food, but there was 

 hardly any opportunity for oviposition. Their behavior was quite 

 normal — that is, when the buildings were heated, they were active, 

 invading ever37thing with their usual annoying persistence, and when 

 the temperatures were low they could be found at rest on the ceiling or 

 walls, especially in the corners. 



During the winter of 1916-17 special attention was paid to the con- 

 ditions existing in the animal house at Bethesda, where large numbers 

 of rabbits and guinea pigs are kept. The building used for this purpose 

 is a long two-story structure, the walls of the first story being of masonry 

 and the second story of frame construction. The floor of the first story 

 is below ground level, and on this floor near the north wall is located the 

 heater of the steam-heating plant. The temperature is maintained at 

 about 60° F. throughout the winter, but in the immediate vicinity of 

 the heater the temperature is, of course, considerably higher. From 

 time to time cabbages were brought in from the storage banks and piled 

 on the floor between the heater and the wall until used for feeding. A 

 certain amount of decay always set in, especially in some of the outer 

 leaves of the cabbages which had previously been slightly frozen. The 



