For some days before, the larva loses its long distinguishing characteristic—its appetite—and now forsakes the plants upon which it formerly fed; or if it does not forsake them, no longer consumes any part of them. It becomes, apparently, in some degree sensible that it is approaching the most dangerous period of the history of the insect—the state of sleep or torpor in which it is to exist as a pupa—of which we shall speak more particularly in our next chapter. Before, although a weak and comparatively a defenceless creature, it was still able to exercise a vigilant watch against its enemies, and thus to avoid them, or to prepare for their reception; but now, its eyes are to be closed in a death-like slumber; its body to hang a tempting bait to any wandering foe, or hungry bird, and it can in no way resist the attacks of the feeblest adversary.

As if fully aware of this, the wonderful instinct of the larva meets the difficulty by teaching it to select the best place for its concealment from a dangerous notice. With this view, it sets out in search of a hiding-place, and rests not until it has obtained a city of refuge which may prove to it a defence against the enemy. It may be some little recess, covered by an irregular stone, and sheltered round the sides by moss and the upspringing grass; or, perhaps, a little hole in the earth has received the poor fugitive from future harm, and in order to conceal itself more completely, it has drawn over the mouth of the cave a covering of leaves. Here, safe from observation, the larva bids a farewell—to speak as the poets speak—to the busy staring world for awhile, and loses all recollection of its past history, in the night of torpidity upon which it has now entered. The larvæ of the lady-bird, and other insects, glue themselves fast to the under side of a twig or leaf, and here pass the days of their sleep in safety. Many of the larvæ of insects whose life, up to this period, has been passed beneath the surface of some glassy pool, now quit the pure element, and seek the shore, on which they are to pass the remaining portion of their existence.

But there are two other ways in which larvæ prepare for the state of pupa, which are so curious, and prevail to such a large extent among insects, that we may be excused for following the example of all authors upon insect history, and treating our readers to the interesting facts which have been recorded by various observers upon this subject. One of these is the plan of hanging themselves up in the air, like sailors in their hammocks; and in other positions, this plan is commonly called the suspension of the larva. The other is the formation of beautiful cases of various kinds, which are called cocoons, in which they wrap themselves up close during the period to be devoted to the pupa state. Let us speak of these each separately; and, first, of the case, or cocoon, as a place of concealment for the larva. It is right, however, to premise, that, while the greater number of insects are in a torpid or half-torpid state while in the pupa form, all are not so, as will be noticed in the next chapter; and those which are not do not of course require the protection of a cocoon, or the contrivance of a silken hammock.

The material of which the case or cocoon is composed is a beautiful silken fibre, which is furnished by a spinning apparatus placed either at the extremity of the body, or more frequently at the mouth of the insect, whence it proceeds in a filament of the utmost delicacy and transparency, but at the same time of considerable tenacity. By its means alone cocoons, of a number of different kinds, some of extraordinary beauty and ingenuity, are constructed; but in other cases the insect has recourse to various materials to assist in giving strength to the walls of its cell.

Cocoon of Silk-worm.

The best example, and the most familiar one we can select of a purely silken cocoon, is that of those

"——spinning worms
That in their green shops weave the smooth-haired silk."

This beautiful and valuable cocoon, when examined externally, appears to be formed in two different ways; for the outer covering is loose and open, while the inner one is compact and close, and so in truth it is, although both coverings are formed of a single thread. The outer has been called the scaffolding, by means of which the inner and more solid covering is constructed. The larva stationing itself between two leaves, or in any other suitable spot, fastens its thread to one of the adjoining surfaces, and then proceeds to draw out the fibre and fasten it in various positions until it has woven around itself an envelope, as it were, of loose gauze. After this has been done it begins to form the closer and more compact structure of the inner envelope, laying on the silk backwards and forwards in a series of zig-zags, until it has laid on several layers, and thus completely shut itself in. The loose outer portion forms what ladies so well know under the title of flos-silk; the inner fibres are the most continuous, admitting of being wound off without breaking, and they form the ordinary silk of commerce.