466 Observations on Habits and Parasites of Common Flies 
Other blow-flies were kept under observation during this period. 
Flies emerging from pupae, obtained from maggots kept in a hot¬ 
house, were placed in a small box with a glass front in a wooden 
shed on Dec. 28. Sugar and water were provided in the box. This 
shed was never heated, and owing to its construction it is pro¬ 
bable that its temperature corresponded closely with that recorded 
in the screen. The flies though protected from the rain and wind 
experienced low temperatures. All the flies, 263 in number, had 
emerged by Jan. 1, 1916. On cold days the flies usually remained 
crowded together without moving much, but were moderately active 
and flew about on warmer days, and were sometimes seen feeding. No 
deaths had occurred by Feb. 12, but 33 had died by Feb. 25. On April 4 
106 (40 %) were still surviving, showing that in sheltered situations these 
flies can live through the winter months. 
The weather conditions during February have just been stated. 
From these observations we may safely conclude that blow-flies 
emerging in the late autumn and winter months can, even without 
shelter, withstand to an astonishing degree cold, rain, snow and wind, 
and that in sheltered situations their chances of surviving the winter 
are considerable. 
Probably the great differences in duration of life and powers of 
resistance between summer and winter flies are correlated with the 
different degrees of activity of the insects. In summer they are ex¬ 
tremely active, and breeding is in progress: in winter on the other hand 
they seldom fly, except on the warmest days, and require very little 
food. 
Flies entering houses. 
Much has been written from time to time on the habits of house-flies 
and other species in dwelhng houses, but up to the present no systematic 
investigation has been undertaken with the view of ascertaining under 
what conditions they enter houses, or the periods during which they 
remain in them. In order to throw some light on this subject records 
were kept throughout the fly seasons of 1914 and 1915 of the numbers 
and species of flies which entered a dining room with a large window 
and garden door, always kept open, facing west. 
The flies were collected at intervals during the day, and killed and 
examined in the evening. Further, during 1915 the flies which came into 
the kitchen, with windows facing south, were left undisturbed, and were 
counted each night about 11.30 p.m. The lights in this room were 
