OYSTER-DRILLS IN THE ESSEX ESTUARIES. 301
in the River Blackwater that Urosalpinx occurred in numbers
on submerged rafts and cages, and suggest that pieces of weighted
wood, submerged and buoyed, would give a large surface for the
drills to collect upon. Such material can be obtained easily and
might be made of a size which could be conveniently hauled
by a boy, who might be employed wholly on the work of collect-
ing drills or tingles in the spring and early summer. There
can be no doubt that trapping tingles in this way, in addition
to reserving all those brought up in the dredges, is an economic
proposition (3).
Experiments carried out in the laboratory at Plymouth
(3 and 6) have shown that Urosalpinx commonly bores through
a young (brood) oyster and eats it in about three days. Larger
oysters are destroyed in about five or six days. Borings can
be made in shells to a depth of rather more than 3 millimetres,
so that quite large oysters are not immune from the attacks of
this pest.
While investigating the feeding habits of Urosalpinx I removed
one individual and placed it on its "back" a few centimetres
from a boring which had just been begun. To my surprise I
found, 30 minutes later, that the same individual had returned
to its boring. I, thereupon, removed the borer again, and again
found that it returned in a short time to its task. The persistent
borer was removed yet again, a third and a fourth time ; it again
returned to the same boring like a dog to its bone, and was then
allowed to complete its task and enjoy its feast. Similar experi-
ments have since been made and it is found that, although the
Urosalpinx will not always return to a boring, it will do so
frequently.
The details of one experiment are as follows:—
Feb. 3 10.0 a.m. A tingle found settling on an oyster.
,, 6.0 p.m. Tingle removed ; a slight circular mark
found just perforating the conchyolin ;
tingle left on its "back" near boring.
7.30 p.m. Tingle resettled on original boring.
Feb. 4 9.30 a.m. Ditto.
,, 5 3.15 p.m. Removed the tingle ; found the shell
nearly bored through ; tingle left on
its back again near the boring.