448 Observations on Habits and Parasites of Common Flies 
263 blow-flies, which emerged in a warm room about Jan. 1, 1916, 
were kept in a box with a glass front in a wooden outhouse, protected 
from the rain and wind. On warm days these flies became active, flew 
about, and took food and water which were provided for them, but during 
cold weather hardly moved. February was a very cold month, but 
by the end of it only 33 had died, and on April 4 106 (40 %) were still 
surviving, showing that in sheltered situations these flies can live 
through the winter months. In May larvae were reared from these flies. 
On warm days during the winter of 1915-16 C. erythrocephala (on 
various dates), M. stabulans 1 $ (Jan. 22), M. pabulorum 1 ? (Feb. 12), 
M. lucorum 2 $ (Feb. 13), E. tenax (Jan. 1) and Anthomyid flies were 
noticed on the windows, and P. cornicina (Jan. 2), E. tenax ? (Jan. 22), 
P. rudis $ (Feb. 13) and several specimens of C. erythrocephala were 
caught sunning themselves in various situations outside. 
The occasional occurrence of blow-flies and other species in rooms 
during the winter months has been recorded for years, and Copeman 
and Austen (1914) collected a number of species from houses in various 
localities during the winter of 1913-14, but came to the conclusion “that, 
the results obtained afford no support to the belief that house-flies 
hibernate in this country in the adult state.” 
The hypothesis, strongly advocated by some writers, that the summer 
generations of house-flies are the descendants of hibernated or “over¬ 
wintered” females seems to be founded on the casual observations of 
stray flies in houses during winter time. 
The writer’s experiments seem to indicate that, amongst most of 
the common species of flies, the very great majority of individuals pass 
the winter as pupae, or more rarely as larvae which pupate early in the 
spring. The pupae or larvae are situated under shelter on the surface 
or are buried within two or three inches of the surface of the ground. 
A very small and unimportant minority of both sexes emerging from 
pupae late in the autumn or even in the winter possibly survive as 
adults till the spring. It is very improbable that many of these females 
are impregnated in the autumn, or that most of them reach sexual 
maturity much earlier than the broods emerging in the spring. 
The emergence of flies from pupae. 
Careful observations were made on blow-flies emerging from their 
puparia and the various stages are illustrated by photographs (Plate 
XXIII). 
Further, by subjecting blow-fly pupae to different conditions an 
