500 Observations on Habits and Parasites of Common Flies 
though less marked, effects on flies. The phenomenon is common in 
hot seasons, and people speak of the flies being “sticky.” 
Flies are most abundant and active on days with several hours of 
bright sunshine after 8 a.m., very little wind, and the “sun” ther¬ 
mometer reaching between 90° F.-100 0 F. On such days throughout 
the season of 1915 the largest numbers were attracted to traps, and 
large numbers were seen flying from flower to flower, and settling on 
palings, etc. Very sunny days on which the sun temperature is higher, 
and the shade temperature unusually high, are not very suitable as the 
flies are lethargic during the hottest hours. On sunny, warm but 
windy days flies may be attracted in moderate numbers to traps, but 
they do not resort to flowers, or settle on palings. Very strong north 
or north-east winds cause almost all activity to cease even on sunny 
days. On bright frosty days in autumn flies leave their shelters to 
bask in the sun. 
Flies are moderately active on warm days with little sunshine, and 
no wind throughout the summer, but such days do not suit them in 
April, May, October or November. 
Flies are lethargic and “sticky ,” visit sheltered places and die in 
large numbers on very - hot, windy, oppressive days with or without 
sunshine. 
Flies seldom leave their retreats on rainy, damp, foggy, cold, or very 
windy days. On poor fly days males are relatively much more active 
than females. 
Chart 7 shows the effects of varying weather conditions on the 
numbers of flies caught in the traps during the season of 1915. 
Outdoor habits of flies. 
(a) Blow-flies confined in an outdoor cage. 
The breeding experiment previously described (p. 458) afforded 
excellent opportunities for studying the outdoor habits of blow-flies, 
and an endeavour was made at the same time by observing “wild” 
flies to ascertain whether they responded to varying conditions in the 
same ways. 
Even in the finest and warmest weather the blow-flies in the cage 
did not begin to move about freely "much before 8.30 a.m. On the 
other hand flies usually emerge from pupae rather earlier in the morning 
(p. 451). 
On sunny days the blow-flies were very active, continually flying 
