There is a caterpillar which forms its silken cone in the shape of a boat turned bottom upwards, whence it is called by Reaumur the “coque en batteau;” the construction is complicated, and seems to require more art than is usually attributed to this insect. It consists of two principal parts, shaped like shells, which are united with considerable skill and propriety; each shell or side is framed by itself, and formed of an innumerable quantity of minute silk rings; in the fore part there is a projection, in which a small crevice may be perceived, which serves, when opened, for the escape of the moth; the sides are connected with so much art, that they open and shut as if framed with springs; so that the cone, from which the butterfly has escaped, appears as close as that which is still inhabited.
Those caterpillars which are not furnished with a silky cone, supply that want with various materials, which they possess sufficient skill to form into a proper habitation, to secure them while preparing for the perfect state; some construct theirs with leaves and branches, tying them fast together, and then strengthening the connection; others connect these leaves with great regularity; many strip themselves of their hairs, and form a mixture of hair and silk; others construct a cone of sand, or earth, cementing the particles with a kind of glue; some gnaw the wood into a kind of saw-dust, and glue it together; with an innumerable variety of modes suited to their present and future state.
To make the reader more fully acquainted with a subject which affords such abundant matter for the exercise of his microscope, I shall proceed to describe, in as concise a manner as I am able, the changes of a few insects of different classes, beginning with the beetle.
The beetle is of the first or coleopterous class, having four wings. The two upper ones are crustaceous, and form a case to the lower ones; when they are shut, there is a longitudinal suture down the back: this formation of the wings is necessary, as the beetle often lives under the surface of the earth, in holes which it digs by its own industry and strength. These cases save the real wings from the damage which they might otherwise sustain, by rubbing or crushing against the sides of its abode; they serve also to keep the wings clean, and produce a buzzing noise when the animal rises in the air. The strength of this insect is astonishing; it has been estimated that, bulk for bulk, their muscles are a thousand times stronger than those of a man!