one's door against a fox or a thief, than to exclude such insidious enemies, whose aversion to light renders it difficult to trace them even when they are

numerous.

We

If we reflect on the prodigious numbers of those insects, and their power and rapidity of destroying, we cannot but admire the wisdom of Providence in creating so indefatigable and useful an agent in countries where the decay of vegetable substances is rapid in proportion to the heat of the climate. have already remarked that they always prefer decaying or dead timber; and it is indeed a very general law among insects which feed on wood to prefer what is unsound: the same principle holds with respect to fungi, lichens, and other parasitical plants.

All the species of Termites are not social; but the solitary ones do not, like their congeners, distinguish themselves in architecture. In other respects, their habits are more similar; for they destroy almost every substance, animal and vegetable. The most common of the solitary species must be familiar to all our readers by the name of wood-louse (Termes pulsatorium, LINN.; Atropos lignarius, LEACH)-one of the insects which produces the ticking, superstitiously termed the death-watch. It is not so large as the common louse, but whiter and more slender, having a red mouth and yellow eyes. It lives in old books, the paper on walls, collections of insects and dried plants, and is extremely agile in its movements, darting, by jerks, into dark corners for the purpose of concealment. It does not like to run straight forward, without resting every half-second, as if to listen or look about for its pursuer, and at such restingtimes it is easily taken. The ticking noise is made by the insect beating against the wood with its head, and it is supposed by some to be peculiar to the female, and to be connected with the laying of her

eggs. M. Latreille, however, thinks that the woodlouse is only the grub of the Psocus abdominalis, in which case it could not lay eggs; but this opinion is somewhat questionable. Another death-watch is a small beetle (Anobium tesselatum).

Structures of Silk spun by Caterpillars, including the Silk-Worm.

"Millions of spinning worms,

That in their green shops weave the smooth-hair'd silk." MILTON'S Comus.

ALL the caterpillars of butterflies, moths, and, in general, of insects with four wings, are capable of spinning silk, of various degrees of fineness and strength, and differing in colour, but usually white, yellow, brown, black, or grey. This is not only of advantage in constructing nests for themselves, and particularly for their pupæ, as we have so frequently exemplified in the preceding pages, but it enables them, the instant they are excluded from the egg, to protect themselves from innumerable accidents, as well as from enemies. If a caterpillar, for instance, be exposed to a gust of wind, and blown off from its native tree, it lets itself gently down, and breaks its fall, by immediately spinning a cable of silk, along which, also, it can re-ascend to its former station when the danger is over. In the same way it frequently disappoints a bird that has marked it out for prey, by dropping hurriedly down from a branch, suspended to its never-failing delicate cord. The leaf-rollers, formerly described, have the advantage of other caterpillars in such cases, by being able to move as quickly backwards as forwards; so that when a bird puts in its bill at one end of the roll, the insects makes a ready exit at the other, and drops along its thread as low as it judges convenient. We

have seen caterpillars drop in this way from one to six feet or more; and by means of their cable, which they are careful not to break, they climb back with great expedition to their former place.*

The structure of their legs is well adapted for climbing up their singular rope the six fore-legs being furnished with a curved claw; while the prolegs (as they have been termed) are no less fitted for holding them firm to the branch when they have re-gained it, being constructed on the principle of forming a vacuum, like the leather-sucker with which boys lift and drag stones. The foot of the common fly has a similar sucker, by which it is enabled to walk on glass, and otherwise support itself against gravity. The different forms of the leg and pro-leg of a spinning caterpillar are represented in the figure.

Leg and Pro-leg of a Caterpillar, greatly magnified. In order, to understand the nature of the apparatus by which a caterpillar spins its silk, it is to be recollected that its whole interior structure differs from that of warm-blooded animals. It has, properly speaking, no heart, though a long tubular dorsal vessel, which runs along the back, and pulsates from twenty to one hundred times per minute, has been called so by Malpighi and others: but *See Insect Transformations, p. 186.

neither Lyonnet nor Cuvier could detect any vessel issuing from it; and consequently the fluid which is analogous to blood has no circulation. It differs also from the higher orders of animals in having no brain, the nerves running along the body being only united by little knobs, called ganglions.* Another circumstance is, that it has no lungs, and does not breathe by the mouth, but by air-holes, or spiracles, eighteen in number, situated along the sides, in the middle of the rings, as may be seen in the following figure from Lyonnet:

Caterpillar of the Goat-Moth (Cossus ligniperda).

These spiracles communicate on each side with tubes that have been called the wind-pipes (trachea).† The spinning apparatus is placed near the mouth, and is connected with the silk-bags, which are long, slender, floating vessels containing a liquid gum. The bags are closed at their lower extremity, become wider towards the middle, and more slender towards the head, where they unite to form the spinning-tube, or spinneret. The bags being in most cases longer than the body of the caterpillar, necessarily lie in a convoluted state, like the intestines of quadrupeds. The capacity, or rather the length of the silk-bags, is in proportion to the quantity of silk required for spinning; the Cossus ligniperda, for example, from living in the wood of trees, spins little, having a bag only one-fourth the length of that of the silk-worm, though the caterpillar is at least twice the dimensions of the latter. The following figure, taken from the *See Insect Transformations, concluding chapter. + Ibid. p. 155.