347 
FURTHER OBSERVATIONS ON THE HABITS AND 
PARASITES OF COMMON FLIES. 
By G. S. GRAHAM-SMITH, M.D. 
University Lecturer in Hygiene , Cambridge. 
(AVith Plates XVIII, XIX, 23 Text-figures and 2 Charts.) 
CONTENTS 
PAGE 
The influence of weather on flies . 
347 
Habits of flies—cleansing .... 
350 
Empusa disease ...... 
353 
Mites . . . . . . ... 
355 
Beetles ....... 
355 
Parasites attacking fly larvae or puparia 
355 
Cynipidae ...... 
356 
Proctotrypidae ..... 
359 
Ichneumonidae ..... 
360 
Chalcididae ...... 
360 
Braconidae ...... 
376 
Conclusions ....... 
382 
THE INFLUENCE OF WEATHER ON FLIES. 
In the year 1915 the flies caught in traps baited with various materials and 
placed in different situations were recorded, and charts constructed showing 
the effects of various meteorological conditions on flies. “ These charts showed 
that the curve for flies caught in traps corresponded most closely to the curve 
for the maximum temperature recorded by a thermometer exposed to the 
sun” (1916, 497 and Chart 5). During the years 1916 and 1917 traps baited 
daily with human excrement were exposed in sunny situations, and the flies 
caught in them recorded. Records of the hours of bright sunshine, of the 
rainfall, the velocity of the wind, the maximum temperatures indicated by 
thermometers exposed to the sun and in the screen, the minimum tempera¬ 
tures in the screen and on the grass were kept. From these observations it 
was possible to compare the effects of meteorological conditions on flies in 
three consecutive seasons. 
Chart 1 shows the mean daily temperatures recorded by a thermometer 
exposed in the sun and the mean daily number of flies caught in a trap exposed 
in the open and baited with human excrement in each week during the seasons 
