Upon the leaves of pear trees we may sometimes find a pretty cocoon of very slight and elegant texture, formed of silk, as shown in the cut.
A very singular cocoon is spun by the larva of a common moth, somewhat of the outline of a balloon in form. This cocoon is spun in a very slight manner, and thus offers a striking contrast to those of many other insects; in fact, it is so slight, and the meshes are so open, that the insect can be readily seen within suspended in a hammock of silk, and thus presenting a very curious appearance. In another, the inclosed insect looks just like a poor prisoner within a grating.
[Illustration: _Cases formed of Epidermis of Bark._]
In order to give a sufficient degree of strength to their cocoons, some larvæ adopt the plan of forming them partly of silken fibre and partly of other materials. Réaumur, being on an entomological excursion in the forest of Vincennes on a fine day in the month of May, fell in with a most curious cocoon, formed by a larva which feeds upon the oak-tree. At first he could scarcely conceive what the object he saw before him was, but on removing the branch it proved to be a very singular cocoon. Detaching a small branch, on which was a larva just commencing its cocoon, Réaumur, finding the evening draw on, set out on his return home. The larva did not seem to discover the fact of its being carried away a prisoner; and as the entomologist carried the branch with gentleness, it proceeded with its task as comfortably as if stationed on the tree it was now leaving behind. Réaumur beguiled the tedium of the way by carefully watching its mode of proceeding in the formation of its cocoon. He thus noticed the larva cutting very delicate layers of the fine upper skin or _epidermis_ of the bark of the twig, which it fastened together by silken cords, and then formed into two wing-like pieces fastened on each side of the twig in the manner represented in the cut, something like the feathers of an arrow in appearance. And now, this being done, the difficulty was to draw the two sides together, and so to convert them into a covering for its body. The manner in which this was done will hardly, perhaps, be imagined. It will be best understood if the reader will cut out two pieces of paper of the shape of these two side portions, fasten them on with a little glue by one of their edges to a piece of twig, and then, by a fine needle and thread, draw them together by stitching from side to side all the way up. The larva does something very like this, for it fixes silk cords to each of the outer edges, and then pulls and hauls with all its might until it has forcibly bent over the layers until they meet, and then it ties the edges together by short cords, so as to produce a seam so beautifully close, even, and fine, as would put the "fine-drawing" of the most superlative tailor to shame; in fact, the join is frequently quite imperceptible. Having done this, it lines the inside with beautiful tapestry of silk. By the time Réaumur and his friends had got to the end of their walk, which occupied an hour and a little more, the larva had, after vast labour, joined together its seams, and far advanced toward the completion of its task.