Parts of a Caterpillar

I N the last lesson we found the full-grown insects very easily. But it is often more difficult to know some of them when they are young. Grasshoppers, crickets, and plant-lice, when they come out of the egg, are very much the same as when they are grown up, except that they have no wings. But the daddy-long-legs begins its life as a grub underground. The lady-bird when young is a kind of caterpillar and runs over the plants eating plant-lice. And beetles are grubs with six small legs before they grow into perfect beetles with wings.

The caterpillars of Moths and Butterflies are easy to find, so we will look at one in this lesson. There is hardly any time in the summer that you cannot find a caterpillar. Those of the Orange-tipped Butterfly come out first in April. In May the Cabbage Butterfly lays her eggs, and soon the caterpillars are eating the young cabbage leaves. A little later you may find among the nettles the black caterpillars with white spots (2, p. 10) which will turn in June into the Peacock Butterfly; or the dark green caterpillars of the Red Admiral. These are hidden in a bunch of leaves generally tied up with caterpillar silk.

If you do not find either of these you cannot miss the heaps of little black caterpillars striped with yellow which feed under the leaves of nettles, and turn into the small Tortoiseshell Butterfly. These caterpillars are very useful in killing nettles, so the butterfly is one you should always be glad to see. Then towards the autumn the caterpillars of the big Hawk-moths do a great deal of mischief. If you go out in the evening or early morning you may find the caterpillar of the Spurge Hawk-moth feeding on the green spurge in the hedges. It is a fine creature three inches long, with three bright lines on its back, and yellow spots on each ring.

But the most common one, which I have often found, is the caterpillar of the Privet Hawk-moth (see coloured picture, p. 20), which feeds in the evening on the privet hedge or the lilac bushes. It is from three to four inches long, and is a bright apple-green, with seven sloping violet stripes on its sides, and a horn at the end of its body. Its head is green, edged with black, and the breathing holes on its sides are circled with bright orange.

It destroys the hedges terribly, for it is very hungry and wants to store up food so that it may grow into a moth. Though its body is soft, its head is hard and horny, and as its mouth has nothing to do in breathing, or making any noise, it can be used all the time for eating. It is made of a great many pieces, but the parts you can see well are the large upper lip (u l) and the two broad strong outer jaws (j) which move to and fro sideways as it gnaws the leaf. As soon as a piece is cut off the caterpillar tucks it into his inner jaws (i j), where it is chewed and swallowed. Under the jaws is the flat lower lip (l l), through which passes a little tube. Look well at this tube (s). It is the place from which comes the silk, which he uses to spin his cocoon, in which he sleeps while his butterfly body is growing.

You remember we read in Book I. that the spider spins her web out of silk which comes from six little pockets under her body. But a caterpillar or a silkworm brings its silk out of its mouth.

Now look at the legs. There are three pairs, one on each ring of the thorax. They have joints in them and claws at the end (2, p. 15). These are true legs, and they are hard and horny like the head. When the caterpillar turns into a moth these six legs will remain. But it has also some cushion feet (see p. 20), on the other rings of its body, which it uses to hold fast to the twigs. These are not true legs, but only fleshy cushions (1, p. 15) with a ring of hooks under them, and they will disappear with the caterpillar's body when the moth grows up. There are generally four pairs of cushion feet behind the true legs, and two pairs at the end of the body, but some caterpillars do not have so many. Do you know those called "Loopers," which bend their body into an arch or loop? You may often find them on the currant bushes, where they do a great deal of mischief. They have only six true legs and four cushion feet at the end of their body, and they walk in a curious fashion. They hold firmly to the twig by their front legs, and then draw up their cushion feet till their body makes a loop in the air. Then they let go with their front legs and lift up their head like an elephant raises his trunk, and stretch forward further up the twig.

As a caterpillar is always eating, his skin becomes so full that there comes a time when he cannot put in any more food. Then he remains quiet for a few hours, and swells out his rings. His skin splits and he creeps out, with a new soft skin ready underneath. This will stretch, and very soon he is eating away as merrily as ever.

He does this about five times in his caterpillar life, and then he stops eating and remains without moving for some days. His colour fades, and when he splits his skin and shuffles it off, all the parts of the butterfly or moth are to be seen underneath, soft and unfinished. Soon a kind of gum oozes out over them. This hardens and keeps the tender body safe from harm while it is growing.

Now he is called a chrysalis, or sometimes a pupa or doll; and, indeed, he looks like a crumpled doll as you see his legs bent together and his head folded down over them under the hard gum. The pupa of a butterfly is generally broad at the top and narrow at the bottom, and it has ridges and prickles on it (3, Plate, p. 10). But the pupas of moths are shaped more like an egg, and are smooth (3, Plate, p. 20). Moths generally wrap their pupa in a silk bag or cocoon, but butterflies leave theirs naked, and fasten it to a stem or a blade of grass with a silken cord (5, Plate, p. 10).

The caterpillar of the Hawk-moth works its way down into the ground and lies in a hole which it lines with silk. I had one in a large flower-pot once for many months. After about seven months, or sometimes much longer, the pupa wriggles up to the top of the ground, and then breaks through its cover and comes out as a moth.

Bring in some caterpillars, each with the plant on which you find it. Keep them fed and watch their changes.