52 NATURAL SELECTION in 



besides children to the belief that they can sting. The 

 curious attitude assumed by sphinx caterpillars is probably a 

 safeguard, as well as the blood -red tentacles which can 

 suddenly be thrown out from the neck by the caterpillars of 

 all the true swallow-tailed butterflies. 



It is among the groups that possess some of these varied 

 kinds of protection in a high degree that we find the greatest 

 amount of conspicuous colour, or at least the most complete 

 absence of protective imitation. The stinging Hymenoptera, 

 wasps, bees, and hornets are, as a rule, very showy and 

 brilliant insects, and there is not a single instance recorded 

 in which any one of them is coloured so as to resemble a 

 vegetable or inanimate substance. The Chrysididse, or golden 

 wasps, which do not sting, possess as a substitute the power 

 of rolling themselves up into a ball, which is almost as hard 

 and polished as if really made of metal, and they are all 

 adorned with the most gorgeous colours. 1 The whole order 

 Hemiptera (comprising the bugs) emit a powerful odour, and 

 they present a very large proportion of gay-coloured and con- 

 spicuous insects. The lady -birds (Coccinellidse) and their 

 allies the Eumorphidae, are often brightly spotted, as if to 

 attract attention; but they can both emit fluids of a very 

 disagreeable nature; they are certainly rejected by some birds 

 and are probably never eaten by any. 



The great family of ground-beetles (Carabidee) almost all 

 possess a disagreeable and some a very pungent smell, and a 

 few, called bombardier beetles, have the peculiar faculty of 

 emitting a jet of very volatile liquid, which appears like a 

 puff of smoke, and is accompanied by a distinct crepitating 

 explosion. It is probably because these insects are mostly 

 nocturnal and predacious that they do not present more vivid 

 hues. They are chiefly remarkable for brilliant metallic tints 

 or dull red patches when they are not wholly black, and are 

 therefore very conspicuous by day, when insect-eaters are 

 kept off by their bad odour and taste, but are sufficiently 

 invisible at night, when it is of importance that their prey 

 should not become aware of their proximity. 



It seems probable that, in some cases, that which would 



1 These colours may, however, be protective by causing the rolled-up insect 

 to look like a piece of shining stoiie or mineral. 



