The cunning caterpillar which finally develops into the Privet Hawk-moth has a slightly more evolved mode of purely theatrical frightening. You see him in No. 6, a full-fed specimen, just ready to turn at once into a chrysalis. This grub feeds usually on the vivid leaves of the privet; he is therefore protectively coloured a bright green, like that of the foliage about him. "But why those great purple stripes on his sides?" you will ask. "Surely they must make him an easy mark for birds?" Not at all: please notice that they run obliquely. There is method in that obliquity. When the caterpillar is smaller, he lurks unseen on the under-side of the leaves, and this pattern of oblique purplish lines exactly imitates the general effect of the shadows cast by the ribs—so much so, that if you look for him on a privet-tree in spring, I doubt whether you will find him till I point him out to you. Even when he waxes fat and full fed, the purple stripes still aid him more or less by breaking up the large green surface into smaller areas, as Professor Poulton has well noticed. He harmonizes better so with the broken masses of the leaves about him. Then again, when the time arrives for him to turn into a chrysalis, he descends to the ground, which, under a thickly-leaved privet bush, is most often brown. So, just as he is coming of age and reaching the proper moment for migration, his back all at once begins to turn brown, in order that he may be less observed as he walks about on the stem; while by the time he is quite ready to take to the earth he has grown brown all over, thus matching the soil in which he has next to bury himself. You could hardly have a better example of the sort of colour-change which often accompanies altered habits of living.
6.—FULL-GROWN CATERPILLAR OF THE PRIVET HAWK-MOTH, SIMILARLY OCCUPIED.
In the illustration, however, you see this really harmless and undefended grub in the act of trying to pretend he is poisonous. He is now mature, and the stripes on his sides stand out conspicuously as he walks on the stem. A sparrow threatens him. He retorts by showing fight—fallaciously and deceptively, for he has nothing to fight with. He lifts his head with an aggressive air, and throws himself about from side to side, as if he knew he could bite, and meant to do it. He also lashes his tail in pretended anger—"I would have you to know, Sir Bird, I am not to be trifled with!" The empty demonstration usually succeeds: the sparrow gets alarmed and believes he means it. This policy is, in essence, that commonly known as "spirited": it consists in trying to frighten your enemy instead of fighting him.
The oddly-marked caterpillar of the Puss Moth carries the same plan of campaign to a much more artistic pitch. This very quaint insect is common on willows and poplars in England, and is on the whole protectively coloured. Black at first, it looks like a mere speck or spot on the leaf; as it grows, it becomes gradually greener, relieved with broad purple patches on the back, which produce the effect of lines and shadows. When quite full-grown, as seen in No. 7, the adult caterpillar generally rests at ease on the twigs of the willow-tree. Our illustration shows it in this final stage of its larval life, just taking alarm and humping its back at the approach of some bird or other enemy. If the alarm continues, it goes through a most curious series of evolutions, admirably shown by Mr. Enock in No. 8. Here, the little beast is altogether on the defensive: it withdraws its head into the first ring of the body, and inflates the margin, which is bright red in colour. Two black spots, which are not really eyes, but which look absurdly eye-like, now give it a grotesque and terrifying appearance. In fact, the inflated ring resembles a hideous grinning mask, and gives the impression of a face with eyes, nose, and mouth, like that of some uncanny creeping creature. But the apparent face is not a face at all: it is artfully made up of lines and spots on the skin of the body. At the same time that the caterpillar thus assumes its mask, it stands on its eight hind legs as erect as it can, and whips out two pink bristles or tentacles from the forked prongs at the end of its tail—you can see them in the picture. It then bends forward the tail, and brandishes or waves about these pink bristles over its false head, so as to present altogether a most gruesome aspect. Indeed, even Mr. Enock's vigorous sketch of the little brute in its tragic moments does not quite convey the full effect of its acting in the absence of colour: for the bright red margin and the swishing pink switches add not a little to the telling smirk and black goggle-eyes of the mask-like face thus produced in terrorem.
7.—CATERPILLAR OF THE PUSS MOTH PREPARING FOR ACTION.
That is not all, either. The Puss Moth caterpillar has a rapid trick of facing about abruptly in the direction of the enemy as if it meant to bite: and this trick is always most disconcerting. If ever so lightly touched, it instantly assumes the terrifying attitude, and presents its pretended face to the astonished aggressor. From a harmless caterpillar it becomes all at once a raging bulldog. Touch it on the other side, and it faces round like lightning in the opposite direction. Professor Poulton tried the effect of its grimace on a marmoset, and found the marmoset was afraid to touch the mysterious creature. We are not marmosets, but I notice that most human beings recoil instinctively from a Puss Moth caterpillar when it assumes its mask. Even if you know it is harmless, there is something very alarming in its rapid twists and turns, and in the persistent way in which it grins and spits at you.
8.—THE SAME CATERPILLAR TERRIFYING AN ENEMY.