Nor is that all. It would clearly be useless for a bright red or yellow caterpillar to hide under a green leaf, and then suppose by that simple device he was going to escape observation. Birds are always looking out for insects under leaves. The consequence is that skulking or lurking caterpillars are soon found out by sharp-eyed and hungry enemies, unless they closely resemble the foliage or stems upon which they lie. From generation to generation, accordingly, the less imitative insects get eaten, and the more imitative spared: so that nowadays, most unarmed caterpillars are green like the leaves or grey like the stems, and are even provided with markings of light and shade upon their skins which mimic the distribution of light and shade among the ribs and veins of the surrounding foliage. Such deceptive leaf-like caterpillars are always very difficult to find: so that careless observers as a rule know only those of the other type, the great hairy "woolly-bears" and the brilliant red and yellow-banded bitter kinds; they never observe the unobtrusive green and brown sorts, which harmonize so admirably with their native tree in colour and markings. [Illustration: 5.--CATERPILLAR OF THE BROAD-BORDERED BEE-HAWK TRYING TO LOOK ALARMING.] Many greenish caterpillars, however, when discovered and disturbed, fall back on their second line of defence: they endeavour to frighten their enemies by devices closely similar to those of the Devil's Coach-horse. The caterpillar of the Broad-bordered Bee-hawk, for example, forms a good instance of a very simple stage in the development of such brazen-faced "terrifying" tactics. This warlike grub is shown in No. 5, trying on its simple little attempt to make itself alarming. Though by no means an uncanny-looking or appalling insect, it will rear itself up on its haunches (so to speak) when attacked, raising the fore part of its body erect with a sudden jerk, and holding its head high, as if it meant to bite or sting, so as to give itself as formidable an aspect as possible. The mild ruse succeeds, too; for birds will eye the harmless creature askance when it attempts this evolution, putting their heads on one side, and ruffling their crests in evident terror. The attitude is all a simple piece of bluff, to be sure, but _it pays_; indeed, bluff in warfare is often more than half the battle. If you put on a bold face in a row, and seem able to take care of yourself, people are apt to think you have a knife up your sleeve, and therefore to refrain from unnecessarily annoying you.