with spines or irritating hairs, and from many being coloured green
like the leaves on which they feed, or being curiously like the twigs
of the trees on which they live. Another instance of protection,
furnished me by Mr. J. Mansel Weale, may be added, namely, that there
is a caterpillar of a moth which lives on the mimosas in South Africa,
and fabricates for itself a case quite indistinguishable from the
surrounding thorns. From such considerations Mr. Wallace thought it
probable that conspicuously coloured caterpillars were protected by
having a nauseous taste; but as their skin is extremely tender, and as
their intestines readily protrude from a wound, a slight peck from the
beak of a bird would be as fatal to them as if they had been devoured.
Hence, as Mr. Wallace remarks, distastefulness alone would be
insufficient to protect a caterpillar unless some outward sign
indicated to its would-be destroyer that its prey was a disgusting
morsel. Under these circumstances it would be highly advantageous to a
caterpillar to be instantaneously and certainly recognised as
unpalatable by all birds and other animals. Thus the most gaudy colours
would be serviceable, and might have been gained by variation and the
survival of the most easily-recognised individuals.
This hypothesis appears at first sight very bold, but when it was
brought before the Entomological Society (33. Proceedings,
Entomological Society, Dec. 3, 1866, p. xlv. and March 4, 1867, p.
lxxx.) it was supported by various statements; and Mr. J. Jenner Weir,
who keeps a large number of birds in an aviary, informs me that he has
made many trials, and finds no exception to the rule, that all
caterpillars of nocturnal and retiring habits with smooth skins, all of
a green colour, and all which imitate twigs, are greedily devoured by
his birds. The hairy and spinose kinds are invariably rejected, as were
four conspicuously-coloured species. When the birds rejected a
caterpillar, they plainly shewed, by shaking their heads, and cleansing
their beaks, that they were disgusted by the taste. (34. See Mr. J.
Jenner Weir s paper on Insects and Insectivorous Birds, in Transact.
Ent. Soc. 1869, p. 21; also Mr. Butler s paper, ibid. p. 27. Mr. Riley
has given analogous facts in the Third Annual Report on the Noxious
Insects of Missouri, 1871, p. 148. Some opposed cases are, however,
given by Dr. Wallace and M. H. d Orville; see Zoological Record,
1869, p. 349.) Three conspicuous kinds of caterpillars and moths were
also given to some lizards and frogs, by Mr. A. Butler, and were
rejected, though other kinds were eagerly eaten. Thus the probability
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