But although the moth is so very plentiful, one hardly ever sees the caterpillar. The reason is that it only feeds by night, and hides away all day long under stones, or beneath small clods of earth, or at the roots of grass. But if you were to go out with a lantern on a mild evening towards the end of April, and search carefully on the grass-stems, you would be able to find it without any difficulty at all. It is dull green in colour, with a darker stripe along the back, and two white ones on each side; and underneath its body it generally has a number of rose-coloured or violet spots. PLATE XL THE PEBBLE HOOK-TIP (3) Five different kinds of “hook-tip” moths are found in the British Islands, and you can tell them at once by the hook-like tip to their front wings. The Pebble Hook-tip is by far the commonest of the five. If you want to find it, the best way to do so is to shake the branches of birch trees, either in May, or in August, for this is one of the “double-brooded” moths. That is, they make their appearance twice in each year, the eggs laid by the spring brood producing moths in the summer, while those laid by the summer brood produce moths in the following spring. The caterpillar of this moth is rather curiously shaped, for its tail--which it always holds up in the air--is drawn out into quite a sharp point. It has a grey head and a light green body, with a purple stripe down the back. It feeds on the leaves of birch trees, and when it has reached its full size it doubles over a corner of one of the leaves, fastens it firmly down by means of a number of silken threads, and then turns into a chrysalis. [Illustration: PLATE XLI 1. Puss 2. Puss Caterpillar] PLATE XLI THE PUSS MOTH (1 and 2) This fine and handsome moth is called the “Puss,” because, when its wings are closed, it looks rather like a brindled cat. And there are two or three smaller moths which are a good deal like it; so these are known as “Kittens.” One does not very often see the Puss Moth, although it is quite a common insect. But you can easily find its caterpillars by looking for them on the leaves of poplar and willow trees in August. They are most odd-looking creatures--bright apple-green in colour, with black heads, and with white and purple stripes upon their backs and sides, and with the front part of the body drawn up into quite a large hump. In front of this hump are two big black spots, which might easily be mistaken for eyes. And at the end of the body are two long, slender horns, from each of which the caterpillar pokes out a pink, thread-like organ when it is frightened. These organs look very much like stings, but they are perfectly harmless, so that you need not be in the least afraid to handle the insect. And the odd thing is that if two or three of these caterpillars are shut up in a box together, they nearly always nibble at one another’s horns.