484 Observations on Habits and Parasites of Common Flies 
examples were noticed on many occasions in different localities in the 
neighbourhood. It appeared early in June, was most abundant in 
September and disappeared at the end of October. 
Flies of the genus Lucilia appeared early in May, and were very 
abundant at the end of August and beginning of September. Towards 
the end of September their numbers diminished very rapidly. 
Pyrellia eriophthalma is never abundant and has a peculiar seasonal 
distribution. Single specimens are not uncommonly found in February 
and March, and moderate numbers in May and June. After this time 
very few specimens are found till the late autumn, when it is not very 
uncommon. 
Pseudopyrellia cornicina appears late, occurring in small numbers 
from June to September, but not becoming abundant until October. 
Pollenia rudis was not uncommon in the early spring and in the 
autumn, but was rare in the summer. These insects rarely visit traps 
except those baited with fruit. Keilin (1915) has shown that its larvae 
develop in the earthworm, Allolobophora chlorotica. 
The habits and distribution of M. domestica have been dealt with in 
detail (p. 470). Only two were caught in traps baited with excrement 
and animal matter throughout the year. 
Musca corvina was not uncommon in the spring and occurred in 
small numbers throughout the late summer months. In Surrey it 
was very abundant during April. This insect was seldom caught in 
the traps. 
Solitary examples of Muscina stabulans were caught throughout 
May, but the majority only emerged in June (p. 452). It was moderately 
abundant throughout the summer. M . pabulorum is less common but 
has the same seasonal distribution. 
Morellia hortorum appeared towards the end of May and disappeared 
in the middle of October. 
Stomoxys calcitrans began to appear in small numbers early in April, 
was common throughout the summer, and most abundant early in 
October. This insect never visits traps. 
Members of the genus Sarcophaga were most abundant in June and 
August, but were caught in small numbers from May to November. 
They were more abundant in 1914. 
Onesia cognat a was very uncommon in 1915, but was abundant in 
1914. Keilin (1915) has discovered that the larvae of this species are 
parasitic in earthworms. 
Hydrotaea dentipes was one of the most abundant flies throughout 
