silk-moth suffers more from the recent disease than the male; and Dr.
Staudinger informs me that in rearing Lepidoptera more females die in
the cocoon than males. With many species the female caterpillar is
larger than the male, and a collector would naturally choose the finest
specimens, and thus unintentionally collect a larger number of females.
Three collectors have told me that this was their practice; but Dr.
Wallace is sure that most collectors take all the specimens which they
can find of the rarer kinds, which alone are worth the trouble of
rearing. Birds when surrounded by caterpillars would probably devour
the largest; and Professor Canestrini informs me that in Italy some
breeders believe, though on insufficient evidence, that in the first
broods of the Ailanthus silk-moth, the wasps destroy a larger number of
the female than of the male caterpillars. Dr. Wallace further remarks
that female caterpillars, from being larger than the males, require
more time for their development, and consume more food and moisture:
and thus they would be exposed during a longer time to danger from
ichneumons, birds, etc., and in times of scarcity would perish in
greater numbers. Hence it appears quite possible that in a state of
nature, fewer female Lepidoptera may reach maturity than males; and for
our special object we are concerned with their relative numbers at
maturity, when the sexes are ready to propagate their kind.
The manner in which the males of certain moths congregate in
extraordinary numbers round a single female, apparently indicates a
great excess of males, though this fact may perhaps be accounted for by
the earlier emergence of the males from their cocoons. Mr. Stainton
informs me that from twelve to twenty males, may often be seen
congregated round a female Elachista rufocinerea. It is well known that
if a virgin Lasiocampa quercus or Saturnia carpini be exposed in a
cage, vast numbers of males collect round her, and if confined in a
room will even come down the chimney to her. Mr. Doubleday believes
that he has seen from fifty to a hundred males of both these species
attracted in the course of a single day by a female in confinement. In
the Isle of Wight Mr. Trimen exposed a box in which a female of the
Lasiocampa had been confined on the previous day, and five males soon
endeavoured to gain admittance. In Australia, Mr. Verreaux, having
placed the female of a small Bombyx in a box in his pocket, was
followed by a crowd of males, so that about 200 entered the house with
him. (81. Blanchard, Metamorphoses, Moeurs des Insectes, 1868, pp.
225-226.)
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