When the caterpillar, which has thus conveyed and disposed a patch of leaf against another leaf, is not ready to be transformed into a chrysalis, it applies itself to make a tent or habitation which it may carry everywhere about with it. It begins by slightly fixing the piece against the perfect leaf, leaving intervals all round, between the piece and leaf, at which it may project its head. The piece which it has fixed serves as a model for cutting out a similar piece in the other leaf. The caterpillar puts them accurately together, except at one end of the oval, where an opening is left for the insect to project its head through. When the caterpillar is inclined to change its situation, it draws itself forward by means of its scaly limbs, riveted upon the leaf. The membraneous limbs, which are riveted against the inner sides of the tents, oblige it to follow the anterior part of the body, as it advances. The caterpillar, also, puts its head out of the tent every time it desires to eat.
There is found on the common chickweed (Stellaria media), towards the end of July, a middle-sized smooth green caterpillar, having three brown spots bordered with white on the back, and six legs and ten pro-legs, whose architecture is worthy of observation. When it is about to go into chrysalis, towards the beginning of August, it gnaws off, one by one, a number of the leaves and smaller twigs of the chickweed, and adjusts them into an oval cocoon, somewhat rough and unfinished externally, but smooth, uniform, and finely tapestried with white silk within. Here it undergoes its transformation securely, and, when the period of its pupa trance has expired in the following July, it makes its exit in the form of a yellowish moth, with several brown spots above, and a brown band on each of its four wings below. It is also furnished with a sort of tail.
On the cypress-spurge (Euphorbia cyparissias), a native woodland plant, but not of very common occurrence, may be found, towards the end of October, a caterpillar of a middle size, sparely tufted with hair, and striped with black, white, red, and brown. The leaves of the plant, which are in the form of short narrow blades of grass, are made choice of by the caterpillar to construct its cocoon, which it does with great neatness and regularity, the end of each leaf, after it has been detached from the plant, being fixed to the stem, and the other leaves placed parallel, as they are successively added. The other ends of all these are bent inwards, so as to form a uniformly rounded oblong figure, somewhat larger at one end than at the other.
A caterpillar which builds a very similar cocoon to the last-mentioned may be found upon a more common plant—the yellow snap-dragon or toad-flax (Antirrhinum linaria)—which is to be seen in almost every hedge. It is somewhat shaped like a leech, is of a middle size, and the prevailing colour pearl-grey, but striped with yellow and black. It spins up about the beginning of September, forming the outer coating of pieces of detached leaves of the plant, and sometimes of whole leaves placed longitudinally, the whole disposed with great symmetry and neatness. The moth appears in the following June.
Cypress-Spurge Caterpillar—(Acronycta Euphrasiæ)—with a Cocoon, on a branch.
It is worthy of remark, as one of the most striking instances of instinctive foresight, that the caterpillars which build structures of this substantial description are destined to lie much longer in their chrysalis trance than those which spin merely a flimsy web of silk. For the most part, indeed, the latter undergo their final transformation in a few weeks; while the former continue entranced the larger portion of a year, appearing in the perfect state the summer after their architectural labours have been completed. (J. R.) This is a remarkable example of the instinct which leads these little creatures to act as if under the dictates of prudence, and with a perfect knowledge of the time, be it long or short, which will elapse before the last change of the pupa takes place. That the caterpillar, while weaving its cocoon and preparing to assume the pupa state, exercises any reflective faculties, or is aware of what is about to occur relative to its own self, we cannot admit. It enters upon a work of which it has had no previous experience, and which is performed, as far as contingencies allow, in the same manner by every caterpillar of the same species. Its labours, its mode of carrying them on, and the very time in which they are to be commenced, are all pre-appointed; and an instinctive impulse urges and guides; and with this instinct its organic endowments are in precise harmony; nor does instinct ever impel to labours for which an animal is not provided. “The same wisdom,” says Bonnet, “which has constructed and arranged with so much art the various organs of animals, and has made them concur towards one determined end, has also provided that the different operations which are the natural results of the economy of the animal should concur towards the same end. The creature is directed towards his object by an invisible hand; he executes with precision, and by one effort, those works which we so much admire; he appears to act as if he reasoned, to return to his labour at the proper time, to change his scheme in case of need. But in all this he only obeys the secret influence which drives him on. He is but an instrument which cannot judge of each action, but is wound up by that adorable Intelligence, which has traced out for every insect its proper labours, as he has traced the orbit of each planet. When, therefore, I see an insect working at the construction of a nest, or a cocoon, I am impressed with respect, because it seems to me that I am at a spectacle where the Supreme Artist is hid behind the curtain.”[BM]
There is a small sort of caterpillar which may be found on old walls, feeding upon minute mosses and lichens, the proceedings of which are well worthy of attention. They are similar, in appearance and size, to the caterpillar of the small cabbage-butterfly (Pontia rapæ), and are smooth and bluish. The material which they use in building their cocoons is composed of the leaves and branchlets of green moss, which they cut into suitable pieces, detaching at the same time along with them a portion of the earth in which they grow. They arrange these upon the walls of their building, with the moss on the outside, and the earth on the inside, making a sort of vault of the tiny bits of green moss turf, dug from the surface of the wall. So neatly, also, are the several pieces joined, that the whole might well be supposed to be a patch of moss which had grown in form of an oval tuft, a little more elevated than the rest growing on the wall. When these caterpillars are shut up in a box with some moss, without earth, they construct with it cells in form of a hollow ball, very prettily plaited and interwoven.
