482 Observations on Habits and Parasites of Common Flies 
Dryomyza flaveola Fab. 
A long, yellow fly bearing a superficial resemblance to S. stercoraria. 
Length. 11 mm.; span of wings 21 mm. 
Head. Yellow. Eyes in both sexes widely separated (1-25 mm.), antennae yellow. 
Arista bare. 
Thorax. Yellow, with darker longitudinal stripes. Strong black bristles laterally, 
but inner and outer dorso-centrals one and two respectively, near scutelluin. 
Wings. Very long and clear. 
Legs. Pale yellow. 
Abdomen. Pale yellow, with long pale hairs on hinder margins of segments. 
firistalis tenax L. The Drone-fly. 
A very large fly resembling a drone bee. Variable in its coloration. 
The peculiar venation of the wings should be noticed. This fly does 
not visit excrement or decaying animal matter, but it is common in 
gardens and is found not infrequently on windows. 
Other species occurring rather less commonly are Musca corvina, 
Morellia hortorum, Onesia cognata, Polietes albolineata, Phaonia erratica, 
Plaiystoma seminationis. Small numbers of many other species are 
found. 
Seasonal distribution and abundance of species. 
From the various records obtained it has been possible to construct 
Chart 4 which probably gives an approximately accurate representation 
of the prevalence of the various common species in the neighbourhood 
of Cambridge during the year 1915. Similar charts compiled for other 
years would probably show slight differences both as to numbers and 
times of relative abundance, but the preliminary observations of 1914 
indicate that the variations would be small except in years with very 
abnormal climatic conditions. 
In constructing this chart the daily weather records were first 
inspected and the most favourable days for flies selected. The numbers 
of each species caught on these days or on other apparently less favour¬ 
able days when very large numbers occurred are represented as columns, 
and the tops of these columns joined to give a curve representing the 
fly population. 
A comparison with Charts 2 and 3 shows that the higher peaks 
probably represent recently emerged specimens of fresh generations, 
