52 NATURAL SELECTION It 
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 Chrysidide, 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. 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 (Coccinellide) and their 
allies the Eumorphide, 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 (Carabide) 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 stone or mineral. 
