AQUATICA IN EPPING FOREST.
11
ponds in Hertfordshire but not yet in Essex ; although I quite
expect to do so when I have carefully worked the ponds in the
Forest. This elegant little fly, whose life-history is yet unknown,
uses its wings for propelling itself through the water, whereas
the other species—Prestwichia aquatica—uses its legs for the same
purpose. The wings are kept closely pressed to the abdomen,
the long cilia converging to a point over the ovipositor, which is
much longer than that of Caraphractus. Its movements are
somewhat jerky, though it manages to paddle about at a fairly
rapid rate.
This strange Hymenopteron has managed to remain un-
recorded for thirty-four years, and hitherto all my efforts to find it
have been unsuccessful until the early part of May of the present
year (1896), when I discovered a few female specimens in a pond
in company with Caraphractus.
In response to a request which I made to the Members of the
Quekett Microscopical Club, to keep a look out for these insects
when "dipping," one of the members, Mr. Scourfield, kindly
sent to me a female Prestwichia which he had taken from a pond
in Epping Forest, and to which I paid several visits, capturing
several females and the hitherto unknown male Prestwichia
aquatica, which proved to be almost apterous, the wings being
very rudimentary and difficult to see even when under the
microscope.
In general appearance the male much resembles a very lean
flea, both in gait and colour. Its head is .01 of an inch broad
and considerably wider than the thorax. The antenna .0125 of an
inch long, consisting of seven joints, the same as in the female, and
of a light testaceous colour. The abdomen the same width as the
thorax from which it gradually tapers to a point. The legs long,
and like the rest of the insect dark brown in colour. The tarsi
are three jointed, with very few hairs on them or on other parts of
the legs.
I am looking forward to following up these interesting aquatic
parasitic Hymenoptera, whose life-histories remain unknown;
this remark applies equally well to all the minute Hymenoptera,
the numbers of which are so great, while the investigators of these
most interesting and useful insects are yet so few.