Homes Without Hands: Being a Description of the Habitations of Animals, Classed According to Their Principle of Construction

The larva of the Goat Moth derives its name from the very powerful and rank odor which it exhales, and which is thought to resemble that of the he-goat. This odor is not only strong but enduring, and for several years after the insect has vacated its burrow the disagreeable scent is plainly perceptible. I have now before me some specimens of the burrow of this creature, and although a very long time has evidently elapsed since the larvæ inhabited them, their odor is quite strong, and can be perceived at a distance of several feet. The pocket in which I placed them, after removing them from the tree, has never lost a rank reminiscence of its contents. As is the case with the musk-beetle, the Goat Moth can be often discovered by means of its odor, and any one who is acquainted with the scent will be attracted by the well-known emanation, and point at once to the tree whence it issues.

The larva is by no means a prepossessing creature, either to the eye or the nostrils, and though some persons believe that it was the famous Cossus, or tree-grub of the Romans, which was thought so great a delicacy by the ancients, I can not believe that any palate could have attained so very artificial a condition as to endure this repulsive creature, much less to consider it as a dainty.

It grows with wonderful rapidity, being when it has reached its full size seventy-two thousand times heavier than when it was hatched; its segments are deeply marked, and in color it is of a mahogany-red above, and yellowish below. The whole surface is smooth and polished, and, as may be presumed, considering the life which it leads, its muscular strength is enormous. Not only are the large and trenchant jaws extremely thick and strong, but the development of muscle is singularly great; and the head is of a wedge-like shape, so that the creature can force itself even through hard wood. It feeds entirely upon the substance of the tree in which it takes up its residence, and leaves in its tunnels a considerable amount of débris. As the creature increases in size, its tunnel increases in diameter; and it is an amusing task to cut up an old and soft-wooded tree, and follow the caterpillar through its manifold windings.

It lives for some three years in the larval condition, and during the winter it lies dormant in an ingeniously made cocoon, constructed from wood-chips and silken thread, a large store of which can be produced by this caterpillar. Several cocoons are now before me, which I took from a willow-tree in Erith marshes. Out of a great number of specimens I have selected four, in order to show the different dimensions of the cocoons. The largest is two inches and a quarter in length, and rather more than an inch in width. In shape it is nearly cylindrical, except at the ends, which are rounded. One of them is intact, but the other has a round hole through which the larva has emerged. It is composed of wood-chips of various sizes, looking like ordinary sawdust, which are loosely, though thickly, fastened upon a silken framework. Near one end of the cocoon the chips are very heavily massed, for what purpose seems doubtful. Rough, however, as is the exterior of the cocoon, the inside is quite smooth and soft, not unlike the interior of the tube made by the trap-door spider.

The smallest cocoon is barely an inch in length, and is made of much smaller chips, fastened together so strongly that the cocoon retains its cylindrical form when handled, whereas the larger specimen is so loosely made that it collapses under the least pressure. The other two are intermediate in point of size, but precisely similar in point of construction. Besides them there is a specimen of the cocoon in which the creature undergoes its last change.

This is of far stronger texture than either of the others, being quite hard, like papier-mâché, and dark and polished within.

Generally, just before the moth emerges, the chrysalis works itself along, so that it partially projects from the hole, thus enabling the insect to escape at once into the outer world. In some instances, however, this is not the case, and in the present specimen the empty chrysalis shell may be seen, its shattered sides showing the manner in which the inclosed moth made its exit. The hole through which the moth emerged from the cocoon is of a wonderfully small size, considering the dimensions of the perfect insect, and its sides are very ragged and irregular. Like the other cocoons, it is strongly imbued with the characteristic odor, which has attached itself so strongly to my fingers that careful ablution will be needed before I shall venture to produce my hands in society.

The course taken by the larva is most erratic. Sometimes it travels just below the bark, and then turns suddenly, and dives into the very heart of the tree. It is much given to making these sudden changes, and frequently returns nearly on its former track, a mere shell of wood dividing the two passages. The winter cocoons may be found in various parts of the tree, some deeply buried in the wood, others near the exterior. The pupal cocoon is, as far as I know from personal experience, very near the exterior of the tree, so that when the perfect insect is freed from its enwrapments, it is obliged to traverse only a very short distance before finding itself in the open air.

To keep this larva until it passes through its different stages is by no means a difficult process, and demands less trouble than is given by the generality of caterpillars. The larva is easily found; for whenever an old willow-tree has a powerful scent, and exhibits certain round holes in its bark, the Goat Moth caterpillar is sure to be an inmate. Cut down the tree, and with a saw and chisel break it up, until the caterpillars are found. The chisel is used as much for ripping as for cutting; and the use of the mallet should be avoided as much as possible, lest the jarring strokes should injure the caterpillar. To the ears of the searcher, a few blows with a mallet on the chisel do not appear very formidable; but to an animal inclosed in the wood the shock of every stroke must be terrible, on account of the sound-conducting power of the substance in which it lies.

When one or two of the caterpillars have been obtained, they should be placed in a metal box, as their sharp jaws would soon force a passage through a wooden prison, and a quantity of the wood should be inclosed with them. No farther trouble is required; for as they eat the dry wood, and do not need to be supplied daily with fresh food, as is the case with the leaf-eating caterpillars, they are quite content, and feed and grow nearly as well as if they had been left in undisturbed possession of the tree in which they were hatched.

Should any of them die, or should a sufficient number be captured to spare a specimen or two, dissection should be employed, in order to show a very peculiar structure, which is probably of use in enabling the caterpillar to make its way through the wood. When laid on its back, and opened, the general structure of the interior resembles that of the silk-worm, save that the muscles are far more strongly defined, and the silk-producing organs are comparatively smaller. Toward the head, however, a pair of organs are seen, which at once arrest the attention. A couple of membranous sacs—something like the honey-bag of the bee, only very much larger, and long in proportion to their width—lie on either side of the neck, if we may so term the first few segments of the larva. They are generally rather flaccid, so that their sides are wrinkled longitudinally. From the upper part of each of these proceeds a delicate thread, which the microscope shows to be hollow; and which is, in fact, a duct leading into the mouth. These sacs contain a very fœtid fluid, which is supposed to moisten the wood, and partly to soften it, so that it can be shredded with comparative ease.

It is hardly necessary to refer the inquiring reader to Lyonnett's magnificent work on this subject, as the book is a model of skill and perseverance. Still, books are chiefly useful as guides, and not as substitutes for practical experience; and though the beautiful work just mentioned may be perfectly familiar, it ought only to act as a guide to the investigator, and not to supply the place of actual dissection.

ANOTHER moth belonging to the same family is also a notable borer into wood. This is the pretty insect called the WOOD-LEOPARD MOTH (Zeuzera æsculi), a rarer moth than that which has just been described, though not by any means a scarce insect when the entomologist knows when and where to look for it.

The larva of the Wood-leopard Moth is rather pretty in color, being whitish-yellow, spotted regularly with black, and having a reddish-brown patch at either extremity. It lives in the interior of many trees, avoiding, however, those which have a very hard-grained wood. Most of the forest trees are subject to its attacks, and the ordinary fruit-trees of our gardens, such as the apple, pear, chestnut, and walnut, are often seriously damaged by this pretty but destructive insect. Like the goat moth, it makes a strong cocoon, in which it can lie safely throughout its pupal condition, and, as with that insect, the walls of the cocoon are rather rough outside and smooth within. When the cocoon is quite dry it is very brittle, and is apt to snap if carelessly handled. This cocoon may often be found when the trees are cut up for firewood; and as it generally lies very near the exterior, a strong pocket-knife will sometimes disclose it.

The perfect insect is remarkably pretty, considering the simplicity of its coloring, which consists of black upon white. The former color, however, is so disposed, that the wings look as if they were made of the minutest miniver, and the feathery antennæ add considerably to its beauty.

Some of the most elegant and curious British Lepidoptera are also among the most destructive.

The various species belonging to the remarkable family Ægeriadæ, properly called Clear-wing Moths, are terrible enemies to the gardener, as well as to the landowner, their larvæ feeding upon the pith, and generally preferring the young wood to that of a more advanced growth. In some cases they live in the roots, and are quite as destructive as their relations who prefer the branches. All the Clear-wings are distinguished by the fact that the greater part of their wings is simply membranous and transparent, without the beautiful feathery scales that are worn by the Lepidoptera as an order. Some of them resemble hornets, others are often mistaken for wasps, while several species are wonderfully like gnats, and as they fly about in the sunshine may readily be mistaken for these insects.

Of one of these insects, Ægeria asiliformis, known to collectors as the BREEZE-FLY CLEAR-WING, Mr. J. Rennie writes as follows: "We observed above a dozen of them, during this summer, in the trunk of a poplar, one side of which had been stripped of its bark. It was this portion of the trunk which all the caterpillars selected for their final retreat, not one having been observed where the tree was covered with bark. The ingenuity of the little architect consisted in scraping the cell almost to the surface of the wood, leaving only an exterior covering of unbroken wood, as thin as writing-paper. Previous, therefore, to the chrysalis making its way through this feeble barrier, it could not have been suspected that an insect was lodged under the smooth wood. We observed more than one of these insects in the act of breaking through this covering, within which there is besides a round movable lid, of a sort of brown wax."