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THE DEATH'S-HEAD HAWK MOTH IN ESSEX.
By WILLIAM S. GILLES, F.R.E.S.
THOUGH by no means uncommonly found in Essex, it
is only in occasional years that the Death's-Head Hawk
Moth (Manduca atropos. L.) is really plentiful. Such a year
has occurred in 1933. The larva is such a large and striking
one, that it naturally arouses considerable interest, and for
the benefit of non-entomological readers I give a short account
of its life-history.
In the first place, there seems no doubt that we owe its
presence in this country to migration from abroad, as there
is a good deal of evidence that the chrysalis is unable to survive
an English winter. The moth, with a wing expanse of 5 inches,
is a powerful flier and heavier than some small birds, so that
it has no difficulty, with a favouring wind, in crossing the English
Channel or even the North Sea. Moths, therefore, in favourable
years, arrive here in May and June: the eggs are deposited
here and there on potato plants and the caterpillars grow rapidly,
stripping the haulm, so that their presence in a field is easily
recognised and detection not difficult. The full-grown larva is
4 to 5 inches long and as thick as one's thumb: it varies in
colour from yellowish-green with lateral violet stripes to brownish-
olive with the lateral stripes darker. The chrysalis is formed
about 6 ins. below ground in an oval earthen cell as big as a hen's
egg, not containing any silk, but made by the larva compressing
the earth, which has been moistened by an exudation, through
movements of its body. The duration of the pupal stage is
variable : the larvae usually pupate in this country towards the
end of August or in the beginning of September. Some of the
moths emerge in the latter part of September and during October;
on the other hand, some of the chrysalides lie over until the
following year, emerging from May till July, if kept out of reach
of frost. By subjecting the chrysalides to warmth and keeping
in moist surroundings, it is usually possible to force out those
that do not naturally emerge in the autumn, in the course of
a week or two. The moth is peculiar among the lepidoptera
as being one of the few that make themselves heard by producing
a squeaking noise, probably as a means of sexual attraction.
The sound is generally considered to be produced in the head
by rubbing the palpi against the base of the proboscis.