206 THE COLOURATION OF INSECTS 



is that they should be as conspicuous as possible in order 

 that their vertebrate enemies may readily recognize them 

 as things to be avoided. The colours of such creatures 

 are therefore known, in the terminology used by Poulton,^ 

 as " warning colours " or " aposemes." 



Obviously it will be to the advantage of such insects 

 that their aposemes should be of simple type to aid recog- 

 nition and memory on the part of the enemy. Hence 

 one finds schemes such as black and yellow alternating 

 rings in a wasp, or, in a butterfly, the wings of one colour 

 except for strongly contrasted patches of another colour, 

 especially at the apex of the fore wing. It is an interesting 

 point that this apical or sub -apical patch of contrasting 

 colour usually has its long axis at right angles to the long 

 axis of the wing. Presumably the transverse direction 

 makes the patch more conspicuous during the movements 

 of the wing than if it were parallel to the long axis of the 

 wing. This point is well shown in the illustrations of 

 the various Planema (see Plates). 



Before dealing with typically aposematic species, it 

 may be said that quite a number of procryptic insects 

 are furnished with an aposeme which they display if 

 an inquiring enemy comes unpleasantly near. The 

 caterpillars of Lasiocampidae, previously alluded to, 

 show, if disturbed, a cleft across the second or third 

 segments, or both, filled with brightly coloured fine 

 sharp spines, which very readily become detached 

 and penetrate one's skin, and would prove very un- 

 pleasant in the mouth of an enemy tasting such a 

 caterpillar for the first time. The colour of the spines 

 varies in different species. It may be orange, or pink, 

 or steely blue-black, but is always such as to make the 

 spines very conspicuous. When the caterpillar is quietly 

 at rest and concealed by its procrypsis, the cleft is closed, 

 but if the caterpillar is disturbed or touched it makes 



1 The Colours of Animals, pp. 336-337. 



