1874, p. 236.) watched for some time two males of an Eristalis courting
a female; they hovered above her, and flew from side to side, making a
high humming noise at the same time. Gnats and mosquitoes (Culicidae)
also seem to attract each other by humming; and Prof. Mayer has
recently ascertained that the hairs on the antennae of the male vibrate
in unison with the notes of a tuning-fork, within the range of the
sounds emitted by the female. The longer hairs vibrate sympathetically
with the graver notes, and the shorter hairs with the higher ones.
Landois also asserts that he has repeatedly drawn down a whole swarm of
gnats by uttering a particular note. It may be added that the mental
faculties of the Diptera are probably higher than in most other
insects, in accordance with their highly-developed nervous system. (21.
See Mr. B.T. Lowne s interesting work, On the Anatomy of the Blow-fly,
Musca vomitoria, 1870, p. 14. He remarks (p. 33) that, the captured
flies utter a peculiar plaintive note, and that this sound causes other
flies to disappear. )
ORDER, HEMIPTERA (FIELD-BUGS).
Mr. J.W. Douglas, who has particularly attended to the British species,
has kindly given me an account of their sexual differences. The males
of some species are furnished with wings, whilst the females are
wingless; the sexes differ in the form of their bodies, elytra,
antennae and tarsi; but as the signification of these differences are
unknown, they may be here passed over. The females are generally larger
and more robust than the males. With British, and, as far as Mr.
Douglas knows, with exotic species, the sexes do not commonly differ
much in colour; but in about six British species the male is
considerably darker than the female, and in about four other species
the female is darker than the male. Both sexes of some species are
beautifully coloured; and as these insects emit an extremely nauseous
odour, their conspicuous colours may serve as a signal that they are
unpalatable to insectivorous animals. In some few cases their colours
appear to be directly protective: thus Prof. Hoffmann informs me that
he could hardly distinguish a small pink and green species from the
buds on the trunks of lime-trees, which this insect frequents.
Some species of Reduvidae make a stridulating noise; and, in the case
of Pirates stridulus, this is said (22. Westwood, Modern
Classification of Insects, vol. ii. p. 473.) to be effected by the
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