216
THE ESSEX NATURALIST.
1917, exactly seventeen years ago to-day, and was placed in
our Museum.1
It appeared that the larva on leaving the water had travelled
frequently ten feet or more, till it found a part of the bank
which rose vertically from the more or less horizontal margin.
The cells found had been made in the angle between the hori-
zontal and vertical surfaces, and their presence was indicated
by a slight convexity and difference of texture of the earth
concealing them. We have not observed a larva actually engaged
in making its cell at the margin of a pond. The chances of such
an opportunity are very small. Having seen, however, just
where the cells are made in nature, it was an easy matter to
reproduce similar conditions at home.
In a small glass tank a layer of earth about two inches
deep and a bank about four inches high and about the same
thickness were made at one end, the earth being damp and
firmly pressed. At the other end of the tank a small shallow
glass vessel was placed, nearly full of water and containing some
water weeds and a nearly mature larva. The larva was supplied
with small earthworms, and when full fed it easily climbed out
of the water and soon discovered the suitably arranged artificial
bank.
The larva could be hindered from commencing its work
for a few hours by placing a glass plate in front of the bank,
but when this was removed it at once started operations.
Suitable larva can be found during July, August and September.
Having selected a suitable spot the larva removes in its
jaws small portions from the face of the earth bank, turns
round and, opening its jaws, pushes out the earth with its front
legs, depositing it to one side or behind it, thus making a hollow
in the bank and forming a curved wall against the face of the
bank. A spherical cavity is thus made in time, about half of
it being within the bank and the remainder beyond its face.
The interior of the cavity is made quite smooth by pressure of
the flat head of the larva. The larva takes about six to eight
hours to dig itself in out of sight, keeping at work almost
continuously.
Lyonnet in his account of the insect2 only says that in the
1 The Essex Naturalist, xviii., 186.
2 Memoires du Mus. d'Hist. Nat. xviii., 415.