be first matured, and thus would procreate a large number of offspring
which would inherit the reduced size of their male parents, whilst the
larger males from being matured later would leave fewer offspring.
There are, however, exceptions to the rule of male insects being
smaller than the females: and some of these exceptions are
intelligible. Size and strength would be an advantage to the males,
which fight for the possession of the females; and in these cases, as
with the stag-beetle (Lucanus), the males are larger than the females.
There are, however, other beetles which are not known to fight
together, of which the males exceed the females in size; and the
meaning of this fact is not known; but in some of these cases, as with
the huge Dynastes and Megasoma, we can at least see that there would be
no necessity for the males to be smaller than the females, in order to
be matured before them, for these beetles are not short-lived, and
there would be ample time for the pairing of the sexes. So again, male
dragon-flies (Libellulidae) are sometimes sensibly larger, and never
smaller, than the females (16. For this and other statements on the
size of the sexes, see Kirby and Spence, ibid. vol. iii. p. 300; on the
duration of life in insects, see p. 344.); and as Mr. MacLachlan
believes, they do not generally pair with the females until a week or
fortnight has elapsed, and until they have assumed their proper
masculine colours. But the most curious case, shewing on what complex
and easily-overlooked relations, so trifling a character as difference
in size between the sexes may depend, is that of the aculeate
Hymenoptera; for Mr. F. Smith informs me that throughout nearly the
whole of this large group, the males, in accordance with the general
rule, are smaller than the females, and emerge about a week before
them; but amongst the Bees, the males of Apis mellifica, Anthidium
manicatum, and Anthophora acervorum, and amongst the Fossores, the
males of the Methoca ichneumonides, are larger than the females. The
explanation of this anomaly is that a marriage flight is absolutely
necessary with these species, and the male requires great strength and
size in order to carry the female through the air. Increased size has
here been acquired in opposition to the usual relation between size and
the period of development, for the males, though larger, emerge before
the smaller females.
We will now review the several Orders, selecting such facts as more
particularly concern us. The Lepidoptera (Butterflies and Moths) will
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