INSECTS.
In this great Class, the Lepidoptera almost alone afford means for
judging of the proportional numbers of the sexes; for they have been
collected with special care by many good observers, and have been
largely bred from the egg or caterpillar state. I had hoped that some
breeders of silk-moths might have kept an exact record, but after
writing to France and Italy, and consulting various treatises, I cannot
find that this has ever been done. The general opinion appears to be
that the sexes are nearly equal, but in Italy, as I hear from Professor
Canestrini, many breeders are convinced that the females are produced
in excess. This same naturalist, however, informs me, that in the two
yearly broods of the Ailanthus silk-moth (Bombyx cynthia), the males
greatly preponderate in the first, whilst in the second the two sexes
are nearly equal, or the females rather in excess.
In regard to Butterflies in a state of nature, several observers have
been much struck by the apparently enormous preponderance of the males.
(74. Leuckart quotes Meinecke (Wagner, Handworterbuch der Phys. B.
iv. 1853, s. 775) that the males of Butterflies are three or four times
as numerous as the females.) Thus Mr. Bates (75. The Naturalist on the
Amazons, vol. ii. 1863, pp. 228, 347.), in speaking of several
species, about a hundred in number, which inhabit the upper Amazons,
says that the males are much more numerous than the females, even in
the proportion of a hundred to one. In North America, Edwards, who had
great experience, estimates in the genus Papilio the males to the
females as four to one; and Mr. Walsh, who informed me of this
statement, says that with P. turnus this is certainly the case. In
South Africa, Mr. R. Trimen found the males in excess in 19 species
(76. Four of these cases are given by Mr. Trimen in his Rhopalocera
Africae Australis. ); and in one of these, which swarms in open places,
he estimated the number of males as fifty to one female. With another
species, in which the males are numerous in certain localities, he
collected only five females during seven years. In the island of
Bourbon, M. Maillard states that the males of one species of Papilio
are twenty times as numerous as the females. (77. Quoted by Trimen,
Transactions of the Ent. Society, vol. v. part iv. 1866, p. 330.) Mr.
Trimen informs me that as far as he has himself seen, or heard from
others, it is rare for the females of any butterfly to exceed the males
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