THE COLORATION OF ANIMALS 71 



American species of Smerinthus, in which they are much less perfectly 

 developed than in the European species. In these SphingidaB, too, the 

 defiant attitude was evolved earlier than the eye-spots, as we may see 

 from our poplar hawk-moth (VSVvi.er^^/i^/ms^^o/mZi), which, when alarmed, 

 spreads out all four wings in the same peculiar manner which in the 

 eyed haw^k-moth (Smerinthun ocellahis) displays the eye-spots; it 

 strikes about with its wings as if to scare off the enemy, an effect which 

 will certainly be more surely achieved if, at the same time, a pair of 

 eyes becomes suddenly visible. 



Sympathetically coloured caterpillars are, however, by no means 

 the only ones ; there are some with such striking, glaring colours that, 

 far from rendering their possessors inconspicuous, they make them 

 visible from a long way off; but this apparent contradiction of the 

 theory of the colour-adaptation of animals that require protection has 

 been explained by the acuteness of Alfred Russel Wallace. We know 

 that among insects, and also among caterpillars, there are many which 

 have a repulsive taste. In any case, certain caterpillars are 

 rejected by many birds and lizards. 

 Such species are, therefore, rela- 

 tively safe from being devoured. 

 If they were protectively coloured, 

 or if, moreover, they resembled 



caterpillars with an agreeable ^^^^^ Caterpillar of a North American 



taste, they would gain little ad- Darapsa in its "terrifying attitude" (after 



, „ ,1 • 1 1 1 M'i Abbot and Smith), 

 vantage from their unpalatabilit}^; 



for the birds w^ould at first take them for eatable, and would only discover 

 their repulsiveness on attempting to eat them. But a caterpillar which 

 has received a sing'le stroke from a bird's bill is doomed to death. It 

 must therefore be of the greatest ad^'antage for unpalatable caterpillars, 

 and unpalatable animals generally, to be in their colouring as con- 

 spicuously distinguishable as possible from the edible species. Hence, 

 then, the glaring colours, wdiich we can now refer without any further 

 difficulty to the process of natural selection, for every individual of an 

 ill-tasting species that is more conspicuously coloured than its fellows 

 must have an advantage over them, and must have a better chance of 

 surviving, because it will be less easily mistaken for a member of an 

 edible species. 



I should like to discuss one other phenomenon, which is well 

 calculated to give us a deeper insight into the transformation pro- 

 cesses of organisms — I refer to the remarkable dimorphism of colour 

 which occurs in many of the species of caterpillar just described. 



The caterpillar of the convolvulus hawk-moth (Sjjhinx convolvuli) 



