The Insect World: Being a Popular Account of the Orders of Insects

these insects is prodigious/'

We will not dwell now on the variableness of the length of the body of caterpillars; on the fleshy appendages which are to be observed on them; on the hairs which either beautify or render them hideous, according to the fancy of the observer \ nor on the various colours with which they are decorated. We will notice these various characteristics when giving the history of some species of remarkable Lepidoptera. Many caterpillars are solitary; others live in companies more or less numerous, either when young, or during the whole of their existence. With the exception of a great number of moths, which live at the expense of our furs, or woollen stuffs, and leather or fatty matters, all caterpillars feed on plants. From the root to the seeds, no part of the vegetable is safe from their attacks. The greatest number of the species, however, prefer the leaves. Those of the most acrid and poisonous are no more spared than those of the most harmless plants. There are caterpillars which eat the leaves of the Euphorbia, or spurge, for instance.

" I wished to try," says Re'aumur, *' the milk of this plant on my tongue. It produced hardly any effect upon it at first; but after a quarter of an hour I found my mouth on fire, and it was a heat which reiterated garglings with water during many hours in succession could not quench. This continued till the next day. The heat passed successively from one part of my mouth to another. I, however, saw many of my caterpillars drinking greedily the great drops of milk which were at the end of the broken stem I had presentedIs it notto them."'extraordinary that there are caterpillars which live on the nettle? — that they eat the leaves of this plant, armed as it is with stinging bristles, which cause such smarting and itching to the skin, and produce blisters upon it.

It has often been said that each plant has its own peculiar species of caterpillar. All we can say is, that a certain number of vegetables only suit certain caterpillars. The species which eat roots are few; those which live in the interior of stalks or stems which they feed on

are numerous, and those which nourish themselves on the pulp of fruits are rare. In general, after the leaves, the caterpillars prefer the flowers: in this they certainly do not show bad taste. Their growth is more or less rapid, according to the species, according to the nourishment they take, and according to the season of the year. Those whose food is succulent grow more rapidly than those which have for their food dry gramineous plants and coriaceous lichens. Most of them eat at night, and remain during the day motionless, and as it were in a state of torpor; others are so voracious that they are constantly eating. This voracity is indeed sometimes surprising. Malpighi has observed that a silkworm often eats in a day mulberry leaves equal to its own weight. How could we provide our horses and oxen with provender, if they required each day their own weight of hay and grass? There are even some caterpillars which are still more voracious than that. Reaumur weighed several caterpillars of a species which lives on the cabbage, and gave them bits of cabbage-leaves which weighed twice as much as their bodies. In less than twenty-four hours they had entirely consumed them. In this space of time their weight increased one-tenth. Fancy a man whose weight is i8o lbs. eating in one day 360 lbs. of meat, and gaining 18 lbs. in weight! Caterpillars eat by the aid of two jaws or mandibles so broad and solid that, considering the smallness of the insect, they are equivalent to all the teeth with which large animals are furnished. Itis by the alternate movement of these mandibles that the caterpillars devour the leaves with so much greediness and ease. " A caterpillar, when it wants to gnaw the edge of a Fig. loi. -Looper Caterpillar eating the leaves of the leaf," says Reaumur, "twists Apricot (after Rdaumuri. its body in such a way that at least one portion of the edge of this leaf is passed between its legs. These legs hold fast that portion of the leaf which is to be cut by the insect's jaws (Fig. 101). To give the first bite the caterpillar elongates its body, and carries its head as far forward as possible. The portion of the leaf which is between the open jaws is cut through the instant the teeth

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meet each other \ the bites succeed each other quickly; there is not one, or scarcely one of them, that does not detach a bit, and each bit is swallowed almost as soon as cut off. At each fresh bite the head approaches the legs in such a way that during the succession of bites it describes an arc; it hollows out the portion of the leaf in a segment of a circle, and it is always in this order that it gnaws it."

But there is a phenomenon in the life of caterpillars which we ought to point out, and which has attracted the attention of the most illustrious observers. All caterpillars change their skins many times during their life. It is not, indeed, enough to say that they change their skins; the skins or cases they cast are so complete that they might be taken for entire caterpillars. The hairs, the case of the legs, the claws with which the legs are provided, the hard and solid parts which cover the head, the jaws — all these are found in the skin which the insect abandons. What an operation for the poor little animal! This labour is so enormous, so troublesome, that one cannot form a just idea of it. One or two days before this grand crisis, the caterpillar leaves off eating, loses its usual activity, and becomes motionless and languid. Their colour fades, their skin dries little by little, they bow their backs, swell out their segments. At last this dried-up skin splits below the back, on the second or third ring, and lets us have a glimpse of a small portion of the new skin, easily to be recognised by the freshness and brightness of its colours. " When once the split has been begun," says Reaumur, " it is easy for the insect to extend it; it continues to swell out that part of its body which is opposite the slit. Very soon this part raises i itself above the sides of the split; it does the work of a wedge, which I elongates it; thus the split soon extends from the end or the cora- I mencement of the first ring as far as the other side of the end of the fourth. The upper portion of the body which corresponds to these j four rings is then laid bare, and the caterpillar has an opening suf- I ficiently large to serve it as an egress through which it can entirely I leave its old skin. It curves its fore part, and draws it backwards; by this movement it disengages its head from under its old envelope, and brings it up to the beginning of the slit; at once it raises it, and puts it out through this slit. The moment afterwards it stretches out its fore part and lowers its head. There now remains for the

I caterpillar nothing but to draw its hinder part from the old case."I This excessively laborious operation is finished in less than a I minute. The new livery which the caterpillar has just put on is fresh and bright in colour. But the animal is exhausted by its fast, and the efforts which it has made. It requires a few hours in which to

regain its equilibrium, and at the same time its former activity and voracity.

The Chrysalis, or Pupa.

Having attained its full development, the caterpillar ceases to eat, as at the approach of a moult, it empties its intestinal canal by copious ejections; it loses its colours, and becomes dull and livid, and thus prepares itself to enter a new phase of its existence.

Some, when about to transform themselves into chrysalides, suspend themselves to foreign bodies. Others spin a cocoon, composed of silk and other substances, which secures them against the attacks of their enemies and the action of the atmosphere. Those which suspend themselves can be divided under two heads, according to the mode of their suspension:— i. Those which suspend themselves perpendicularly by the tail. 2. Those which, after having fixed themselves by the same part, suspend themselves horizontally, by means of a silk thread passed round the body.

To understand the difficulty which the first of these operations presents, we must consider the problem which the caterpillar has to solve. In this problem there are two unknown quantities to be discovered. Firstly, the caterpillar must suspend itself firmly; and secondly, the pupa, having no communication with the object which supports it, must be suspended in the same manner. This problem is. difficult, apparently impossible, to solve. It is only by watching these insects at work that one can discover the wonderful mysteries of their lives. Swammerdam, Vallisnieri, and other observers who have studied insects, had not, however, observed the manoeuvres of caterpillars in this curious phase of their existence. It is to Reaumur again that science is indebted for the most charming and valuable observations on this point. He got together a great number of caterpillars of the small Tortoise-shell Butterfly ( Vanessa urticce)^ black prickly caterpillars which are common on the stinging-nettle, where they live in companies, and suspend themselves by the tail. When the time approaches at which the caterpillars of this species ought to undergo their transformations, they usually leave the plant which had up to that time served them as food. After having wandered about a little, they select some convenient spot, where they hang themselves up head downwards (Figs. 102, 103).

In order to hang itself in this way, the caterpillar begins by covering, with threads drawn in different directions, a pretty large extent of the surface of the body against which it wishes to fix itself. After having covered it thus with a kind of thin cobweb, it adds different

H7 LEPIDOPTERA.

layers of threads on a small portion of this surface, in such a manner that the upper one is always smaller than that upon which it is laid. In this manner a small hillock of silk is formed, the tissue of which is not at all compact. It resembles an assemblage of loose or badly interwoven threads. The membranous feet of the caterpillar are armed with hooks of different lengths, with the aid of which it suspends itself. By alternately contracting and elongating its body, it pushes its hindermost legs against the hillock of silk, presses against it the hooks of its feet, so as to get them better entangled, and lets its body Figs. jo2, 103 Caterpillars of the small Torfofse-shell fall in a vertical position. Butterfly {Vanessametamorphoses.urticce) undergoing their

It remains hanging thus, often for twenty-four hours, during which time it is occupied in a difficult task, that of splitting its skin. In order to effect this, it incessantly curves and recurves its body (Fig. 102), until at last a split appears on the skin of the back, and through this split emerges a part of the body of the chrysalis. This acts as a wedge, and little by little the split widens from the head to the last of the true legs, and beyond them. Then the opening is sufficient to allow of Figs. 104, 105. — Chrysalides of the small Tortoise-the chrysalis drawing out its shell ButterflyCaterpillarfreeing themselvesskin. from the anterior portion from the envelope, which it immediately does. To set itself entirely free, the chrysalis lengthens and shortens itself alternately (Fig. 105). Each time that it shortens itself, and when it consequently distends the part of its body which is outside the old skin, that parts acts against