128 
JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 
and active Wasp Fly (fig. 21), and soon meets its partner, and 
again another batch of eggs is laid where Green Flies most do 
congregate. I consider it the bounden duty of every gardener 
to become acquainted with the Wasp Flies in all their changes, 
and to conscientiously avoid killing them. 
Some of the Green Flies may even contain “ blessings ” in the 
shape of minute 
parasitic Flies. 
One of these is 
shown at fig. 22. 
A little experience 
and patience will 
soon enable any¬ 
one to detect these 
very fat Flies, 
which generally 
lose their green 
colour, and attach 
themselves some¬ 
what apart from 
their fellows, and 
gradually become 
of a dry appear¬ 
ance and brown 
or white in colour. 
From each of 
these emerge 
small four-winged 
Flies of different 
species, the most 
Fig. 20. plentiful (Aphi- 
dius) being shown 
at fig. 22. These and other allied species are in the habit 
of running about the green Flies, tapping them on the back 
with their long antennae and sounding them to ascertain if 
they already contain a parasitic grub ; if not a rapid leap is taken 
upon the back of one, and nolens volens a hole bored through 
the skin and an egg of the parasite deposited in the stomach of 
the Green Fly. This egg soon hatches to a maggot which feeds 
upon the juices contained, and of course in due time destroys 
