72 MIMICRY, AND OTHER PROTECTIVE 
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 in- 
animate 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 propor- 
tion of gay-coloured and conspicuous insects. The 
lady-birds (Coccinellide) and their allies the Hu- 
morphide, 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- 
