538 Observations on Habits and Parasites of Common Flies 
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. 
3. The wintering habits of M. domestica are still obscure. 
4. The time occupied by the various stages through which a fly 
passes from the moment when the puparium ruptures to the time when 
the fly is fully formed and normally coloured varies with the temperature. 
5. The majority of specimens of each species only emerge from 
“winter” pupae after the mean temperature of the materials in which 
the pupae pass the winter reaches a certain “critical” point, which 
differs for each species. 
6. The “critical” point for C. erythrocephala, F. manicata, and 
F. scalaris seems to be about 48-50° F., and for 0. leucostoma about 63° F. 
7. In several species the majority of males emerge before the females. 
8. Flies emerging from “winter” pupae seem to be the most 
hardy. Many of the flies of subsequent generations only live a few 
days, and never reach sexual maturity. 
9. The estimations of the multiplication of flies during the fly 
season are very much exaggerated. Amongst blow-flies confined in a 
large open-air cage, and protected from many of their enemies and 
certain adverse conditions, the descendants of each female only numbered 
130 individuals. Amongst “wild” flies the increase must be con¬ 
siderably smaller. 
10. The normal duration of life amongst blow-flies is about 30 days 
iu the summer. 
'll. A considerable mortality amongst flies often follows cold, wet 
and windy days. Oppressive sultry weather is productive of the 
greatest mortality. Flies die if exposed to very hot sunshine. 
12. During the season many different species of flies enter rooms. 
It seems evident that members of most of the species enter by accident, 
but at least four species, C. erythrocephala, S. calcitrans, F. canicularis 
and M. domestica enter designedly with the intention of remaining 
indoors for longer or shorter periods. C. erythrocephala is attracted 
into rooms for the purpose of depositing eggs on meat. It seldom 
remains long indoors. S. calcitrans enters for shelter, and F. canicularis 
for some purpose at present unknown (p. 469). M. domestica remains 
indoors for considerable periods. Possibly in this species the develop¬ 
ment of the ova requires a high temperature, and the flies remain 
indoors till they are ready to deposit eggs. 
