The astonishing task of supplying silk for the whole civilized world is performed almost without exception by the common silkworm, or caterpillar of the mulberry-tree moth. But it must not be supposed that this is the only silk-producing insect. On the contrary, all the caterpillars of butterflies and moths have the power of spinning a certain quantity of silken thread, however small, and however inferior to that of the silkworm, properly so called. It is very common in gardens to see numbers of caterpillars dangling by their silken threads from the young branches of fruit-trees. In this way they let themselves down, or break their fall if blown off by the wind, or otherwise shaken from their favourite tree. And in the case of some caterpillars when the insect has completed the term of its existence and becomes a chrysalis, it suspends itself by silken cords to some fixed point, where it remains in complete repose, without food, perhaps for months before the perfect winged insect bursts forth, as different a creature from the caterpillar as the chrysalis is from either,—and yet these are but three different states of existence of the same insect. [Illustration: CHRYSALIS SUSPENDED BY SILKEN CORDS. ] According to the particular species of caterpillar, the silk will vary in strength and fineness, and also in colour, but seldom will it be found strong enough, or in sufficient quantity to be of use to us. The insects themselves employ it in many ways for their own safety and shelter. How common it is to find some of the leaves of a lilac-tree made up into little rolls, or folded together at their edges, where they stick so fast that it requires some little force to pull them asunder. This is the work of a small caterpillar, whose subsistence is found on that tree. A single egg has been laid on each leaf selected by the parent moth, and soon after it is hatched, the caterpillar begins rolling up the lilac leaf, and fastening the edges with silk. This is a work of time, but gradually proceeds as the caterpillar increases in strength, until at last it is shut up in a gallery of its own making, safe from the attacks of birds and larger insects. The leaves of various other trees are rolled in a somewhat similar manner, as those of the oak, the willow, and the rose, and also those of humbler plants, as the plantain, nettle, thistle, &c. The mode in which these leaf-rolling caterpillars set to work to form convenient habitations of the leaves of the plants on which they feed, is well described by Kirby and Spence. [Illustration: OAK LEAF ROLLED BY A CATERPILLAR. ]