MIMICRY 85 



long period during the year. Here the individuals turn 

 white in the winter. 



In insects, again, we find that large groups of butterflies, 

 distasteful to insectivorous birds, though not related to each 

 other, resemble each other nearly in coloration. " The central 

 types in these groups belong to sub-families which are more 

 abundant and even more unpalatable than the generality of 

 their orders." l Insects possessing stings and other means of 

 defence are closely resembled by quite different orders of in- 

 sects that are quite defenceless. Among the commonest forms 

 imitated are wasps and ants (Hymenoptera). These stinging 

 or biting insects are frequently imitated by flies (Diptera), 

 bugs (Hemiptera), moths (Lepidoptera), spiders (Arachnida), 

 and beetles (Coleoptera). The most striking feature in these 

 resemblances is that they are arrived at in quite different 

 ways by insects that are related to each other. Thus, for 

 instance, in Lepidoptera the transparency of the wings, 

 necessary to resemble the wings of a wasp or the trans- 

 parent wings of other distasteful butterflies, may be gained 

 by the " loose attachment of the scales, so that they easily 

 and rapidly fall off, and leave the wings bare, except for 

 a marginal line and along the veins." In others the scales 

 remain, but become transparent. They may also be set 

 upon edge, so allowing the light to pass freely between 

 them. 2 In beetles the wing-cases may be coloured so as 

 to represent the coloration and shape of the body of the 

 wasp or ant imitated. The narrow waist may be repre- 

 sented by white marks which tend to conceal the real shape 

 of the outline and make it appear like that of the model. 

 In other beetles the wing-cases are so reduced as to show 

 the under-wings which closely resemble those of a wasp. 

 " Furthermore, the elytra (wing-cases) are reduced in two 

 different ways in some genera to linear rudiments more 

 or less broadened at their bases ; in others to small sub- 

 quadrate or oval structures representing the bases alone." 3 



1 Poultou, op. cit., p. 233. 2 Ibid., pp. 251 and 266. 



3 Ibid., p. 252. 



