G. 8. Graham-Smith 
441 
Introduction. 
Within the last few years several books and numerous papers have 
been published dealing with various problems relating to the life-histories, 
and disease-spreading capacities, of house-frequenting and other non¬ 
biting flies. An intimate knowledge of the habits of flies is essential 
if the most suitable methods are to be devised in order to diminish 
their numbers, yet it is only too evident that many of the accepted 
hypotheses are founded on the most superficial observations, and that 
extensive and carefully planned experiments, with a few notable excep¬ 
tions, are conspicuously absent. 
In 1912 the writer decided to attempt to investigate some ot the 
problems, which have received little attention, including amongst others 
the wintering; habits of flies, their seasonal distribution, and the succession 
of generations. Extensive preliminary investigations were carried out 
especially in the winter of 1913-14, and the summer of 1914. Ehes of 
various species were bred from pupae, which had passed through the 
winter under natural conditions, flies of all species were collected daily 
from windows and recorded, traps of different kinds baited with various 
materials were used for catching flies out of doors, and records of the 
rainfall, barometric pressure, temperatures in various situations and 
daily weather conditions were kept. During the winter of 1914 the 
flies collected were carefully examined, and specimens of most of the 
commoner species were identified by Mr Percy H. Grimshaw 1 , to 
whom the writer is very greatly indebted for all the trouble he has 
taken. The other observations recorded were also carefully studied, 
including the effects of the weather conditions. 
Owing to periods of absence from Cambridge, omissions in the 
records, insufficient control experiments and other causes it was decided 
not to publish any records of these observations, but to make use of 
the large amount of information acquired and the experience gained 
in devising more elaborate investigations and experiments to be con¬ 
tinued throughout the fly season of 1915. It was decided to attempt 
to ascertain the ways in which various common species pass the winter, 
the factors which cause different species to appear at different times, 
the extent to which multiplication occurs under natural conditions, 
the effects of varying weather conditions on different species, their 
habits in regard to entering houses, visiting decaying animal matter 
and human excrement, and certain other points of less importance. 
1 Specimens identified by Mr Grimshaw are marked *. 
