PDF - Wallace Online

52 NATURAL SELECTION inbesides children to the belief that they can sting. Thecurious attitude assumed by sphinx caterpillars is probably asafeguard, as well as the blood -red tentacles which cansuddenly be thrown out from the neck by the caterpillars ofall the true swallow-tailed butterflies.It isamong the groups that possess some of these variedkinds of protectionin a high degree that we find the greatestamount of conspicuous colour, or at least the most completeabsence of protective imitation. The stinging Hymenoptera,wasps, bees, and hornets are, as a rule, very showy andbrilliant insects, and there is not a single instance recordedin which any one of them is coloured so as to resemble avegetable or inanimate substance. The Chrysididse, or goldenwasps, which do not sting, possess as a substitute the powerof rolling themselves up into a ball, which is almost as hardand polished as if really made of metal, and they are alladorned with the most gorgeous colours. 1 The whole orderHemiptera (comprising the bugs) emit a powerful odour, andthey present a very large proportion of gay-coloured and conspicuousinsects. The lady -birds (Coccinellidse) and theirallies the Eumorphidae, are often brightly spotted, as if toattract attention; but they can both emit fluids of a verydisagreeable nature; they are certainly rejected by some birdsand are probably never eaten by any.The great family of ground-beetles (Carabidee) almost allpossess a disagreeable and some a very pungent smell, and afew, called bombardier beetles, have the peculiar faculty ofemitting a jet of very volatile liquid, which appears like apuff of smoke, and is accompanied by a distinct crepitatingexplosion. It is probably because these insects are mostlynocturnal and predacious that they do not present more vividhues. They are chiefly remarkable for brilliant metallic tintsor dull red patches when they are not wholly black, and aretherefore very conspicuous by day, when insect-eaters arekept off by their bad odour and taste, but are sufficientlyinvisible at night, when it is of importance that their preyshould not become aware of their proximity.It seems probable that, in some cases, that which would1 These colours may, however, be protective by causing the rolled-up insectto look like a piece of shining stoiie or mineral.