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Show 416 SEXUAL SELECTION. PART IL serve in any ordinary manner as a protection. .As an iustance of this, Mr. Bates informs me that the most conspicuous caterpillar which he ever beheld (that of a Sphinx) lived on the large green leaves of a tree ~n the open llanos of South America ; it was about four mchcs in lenotb, transversely banded with black and yellow, and with its head, legs, and tail of a bright rer1. Hence it caught the eye of any man who passed by at ~he distance of many yards, and no doubt of every passmg~ bird. I then applied to Mr. vVallace, who has a~ inn~te f!enius for solvin<Y difficulties. .After some cons1deratwn, <) 0 • • he replied : " Most caterpillars r~qmre ~rotectw~, as " may be inferred from some kmds bemg furmsl:ed " with spines or irritating hairs, and fro~ many bemg " coloured green like the leaves on whwh th~y feed, ':or curiously like the twigs of the trees on whwh t?ey " live.'' I may add as another instance of pt:otectwn,. that there is a caterpillar of a moth, as I am mformed by Mr. J. Mansel "\Veale, which lives on the mim?sas in South .Africa, and fabricates for itseJf ·a case, qmte undistin()' uishable from the surrounding thorns. From such ~onsiderations Mr. Wallace thought it probable that conspicuously-coloured caterpillars ~ere ~ro~ected by having a nauseous taste ; but as then skm IS extremely t ender, and as their intestines readily protn~de from a wound, a slight peck from the beak of a bud 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~ CHAP. XI. SUMMARY ON INSECTS. 417 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 32 it was supported by various statements ; and Mr. J. Jenner Weir, who keeps a large number of birds in an aviary, has made, as he informs me, numerous 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 conspicuouslycoloured 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.33 Three conspicuous kinds of caterpillars and moths were also given by Mr . .A. Butler to some lizards and frogs, and were rejected ; though other ldnds were eagerly eaten. Thus the probable truth of Mr. Vl allace's view is confirmed, namely, that certain caterpillars have been made conspicuous for their own good, so as to be easily reco<Ynised by their enemies, on nearly the same principl; that ce;tain poisons are coloured by druggists for the good of man. This view will, it is probable, be hereafter extended to many animals, which are coloured in a conspicuous manner. Summary and Concluding Remarks on Insects.Looking back to the several Orders, we have seen that the sexes often differ in various characters, the meanillg a2 • Proc. Eutomolog. Soc.' Dec. 3rd, 1866, p. xlv., and March 4th, 1867, p. lxxx. . . . . aa See Mr. J. Jenner Weir's paper on mseets and msechvorous b1rds, in 'Transact. Ent. Soc.' 1869, p. 21 ; also Mr. Butler's paper, ibid. p. 27, VOL. I. ~ E |