It is by the action of the hinder pair of its legs that the ant-lion drags itself backwards, the other four pair being extended trailing after it, and leaving an impression on the surface of the fine sand over which it has passed; and when burrowing its way beneath the surface of the sand, it proceeds by short steps backwards. A portion of sand at each step is thrown on the head, owing to the hump-like form of the back: this is immediately jerked away, the body at the same time advancing another step in its backward and spiral motion. Where it rests, a little hillock of sand is raised by the body of the ant-lion underneath; while its jaws emerge and spread flat on the surface. It now probably commences its pitfall, the mode of excavating which we have given in detail. From the spiral course described by the ant-lion in its backward progress appears to have arisen the idea of its tracing out a circle as the outline of its pitfall—as would an architect or engineer; but whence sprang the often-repeated statement, that the ant-lion loads its head with sand by means of one of its legs, that nearest the centre of the circle, we cannot conjecture. Nor do we know how, as it works entirely buried with the exception of the head, the ant-lion can act when it meets with a stone or other obstacle, as M. Bonnet states he has repeatedly witnessed. He observes that if the stone be small, it can manage to jerk it out in the same manner as the sand; but when it is two or three times larger and heavier than its own body, it must have recourse to other means of removal. The larger stones it usually leaves till the last; and when it has removed all the sand which it intends, it then proceeds to try what it can do with the less manageable obstacles. For this purpose it crawls backwards to the place where a stone may be, and thrusting its tail under it, is at great pains to get it properly balanced on its back, by an alternate motion of the rings composing its body. When it has succeeded in adjusting the stone, it crawls up the side of the pit with great care, and deposits its burthen on the outside of the circle. Should the stone happen to be round, the balance can be kept only with the greatest difficulty, as it has to travel with its load upon a slope of loose sand, which is ready to give way at every step; and often when the insect has carried it to the very brink, it rolls off its back and tumbles down to the bottom of the pit. This accident, so far from discouraging the ant-lion, only stimulates it to more persevering efforts. Bonnet observed it renew these attempts to dislodge a stone five or six times. It is only when it finds it utterly impossible to succeed, that it abandons the design and commences another pit in a fresh situation. When it succeeds in getting a stone beyond the line of its circle, it is not contented with letting it rest there; but, to prevent it from again rolling in, it goes on to push it to a considerable distance. We maybe pardoned for pausing before we give full credence to these details.
The ant-lion feeds only on the blood or juice of insects; and as soon as it has extracted these, it tosses the dry carcase out of its den.
When it is about to change into a pupa, it proceeds in nearly the same manner as the caterpillar of the water-betony moth (Cucullia scrophulariæ). It first builds a case of sand, the particles of which are secured by threads of silk, and then tapestries the whole with a silken web. Within this it undergoes its transformation into a pupa, and in due time it emerges in form of a four-winged fly, closely resembling the dragon-flies (Libellulæ), vulgarly and erroneously called horse-stingers.
The instance of the ant-lion naturally leads us to consider the design of the Author of Nature in so nicely adjusting, in all animals, the means of destruction and of escape. As the larger quadrupeds of prey are provided with a most ingenious machinery for preying on the weaker, so are those furnished with the most admirable powers of evading their destroyers.
In the economy of insects, we constantly observe that the means of defence, not only of the individual creatures, but of their larvæ and pupæ, against the attacks of other insects, and of birds, is proportioned, in the ingenuity of their arrangements, to the weakness of the insect employing them. Those species which multiply the quickest have the greatest number of enemies. Bradley, an English naturalist, has calculated that two sparrows carry, in the course of a week, above three thousand caterpillars to the young in their nests. But though this is, probably, much beyond the truth, it is certain that there is a great and constant destruction of individuals going forward; and yet the species is never destroyed. In this way a balance is kept up, by which one portion of animated nature cannot usurp the means of life and enjoyment which the world offers to another portion. In all matters relating to reproduction, Nature is prodigal in her arrangements. Insects have more stages to pass through before they attain their perfect growth than other creatures. The continuation of the species is, therefore, in many cases, provided for by a much larger number of eggs being deposited than ever become fertile. How many larvæ are produced, in comparison with the number which pass into the pupa state; and how many pupæ perish before they become perfect insects! Every garden is covered with caterpillars; and yet how few moths and butterflies, comparatively, are seen, even in the most sunny season? Insects which lay few eggs are, commonly, most remarkable in their contrivances for their preservation. The dangers to which insect life is exposed are manifold; and therefore are the contrivances for its preservation of the most perfect kind, and invariably adapted to the peculiar habits of each tribe. The same wisdom determines the food of every species of insect; and thus some are found to delight in the rose-tree, and some in the oak. Had it been otherwise, the balance of vegetable life would not have been preserved. It is for this reason that the contrivances which an insect employs for obtaining its food are curious, in proportion to the natural difficulties of its structure. The ant-lion is carnivorous, but he has not the quickness of the spider, nor can he spread a net over a large surface, and issue from his citadel to seize a victim which he has caught in his out-works. He is therefore taught to dig a trap, where he sits like the unwieldy giants of fable, waiting for some feeble one to cross his path. How laborious and patient are his operations—how uncertain the chances of success! Yet he never shrinks from them, because his instinct tells him that by these contrivances alone can he preserve his own existence, and continue that of his species.
CLOTHES-MOTH AND OTHER TENT-MAKING CATERPILLARS.—LEAF AND BARK MINERS.
There are at least five different species of moths similar in manners and economy, the caterpillars of which feed upon animal substances, such as furs, woollen cloths, silk, leather, and, what to the naturalist is no less vexing, upon the specimens of insects and other animals preserved in his cabinet. The moths in question are of the family named Tinea by entomologists, such as the tapestry-moth (Tinea tapetzella), the fur-moth (Tinea pellionella), the wool-moth (Tinea vestianella), the cabinet-moth (Tinea destructor, Stephens), &c.