Gr. S. Graham-Smith 
473 
After October 25 it is improbable that many flies entered, and the 
numbers present gradually decreased till all had disappeared on Dec. 12. 
In order to obtain some more definite information on this point 
31 house-flies, caught in another room, were marked with yellow chalk 
and liberated in the kitchen on August 23. Only one was found there 
next day, and two specimens were found in other rooms in the house. 
The others had disappeared. The process of marking seemed to have 
such a disturbing effect on the flies that as a means of investigating 
their habits the method was abandoned. 
Possiblv the development of the ova requires a high temperature 
and the flies remain until they are ready to lay their eggs, which seem 
never to be deposited on food in kitchens. 
In Jepson’s (1909) “observations on the breeding of Musca domestica 
during the winter months” no mention is made of the finding of eggs 
or larvae in the very hot bake-house and sculleries where the adults 
were found, though experimentally they could be induced to oviposit. 
Useful information might be obtained by keeping adult house-flies 
at various temperatures in order to ascertain whether impregnation 
and the development of the ova within the female are inhibited below 
certain temperatures. It was noticed (p. 508) that house-flies kept 
outside in cages laid very few eggs, suggesting that the temperature 
conditions were unfavourable. 
Such experiments might furnish the explanation of the flies’ habit 
of entering and remaining in warm rooms. 
Observations by means op traps on the factors influencing 
THE OUTDOOR HABITS OF FLIES. 
Purposes of the investigations. 
During the summer of 1914 a large number of preliminary observa¬ 
tions on the habits of various flies by means of traps were undertaken 
with the intention of gaining experience in the most suitable methods 
for conducting more extensive investigations in 1915. It was noticed 
that the forms and situations of the traps, the baits, the weather and 
the period of the season all exerted marked influences. 
The observations about to be described were made in a garden, 
50 yards long and 14 yards wide, adjoining on the north a cultivated 
garden, on the west a large school playing field surrounded by cultivated 
fields, on the south an uncultivated patch of ground and on the east 
