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

Certain enemies, however, care nothing for this hairy defense, these foes but swallow the caterpillar without hesitation. Chief among them is the cuckoo, which feeds largely on the caterpillar of the Tiger Moth, and, in consequence, is subject to a very remarkable phenomenon. The interior of the gizzard had long been known to be lined with hair, which was thought to be a natural and ordinary growth peculiar to the species. It was however discovered—I believe by John Hunter—that these hairs are those of the Tiger Moth, the points of which have worked themselves into the coats of the organ in which they were found. Hunter employs this fact as an illustration of the power and peculiar movement of the gizzard.

Doubts have been thrown upon the accuracy of Hunter's statement; but the question has been set at rest by two facts. In the first place, cuckoos that have been held in confinement do not possess the hairy lining; and, in the second place, the microscope proves that the hairs are those of a caterpillar, allied at least to the Tiger Moth, if not belonging to the insect itself.

When the caterpillar has ceased feeding, and is about to become a pupa, it ascends some convenient object, and then spins a beautiful cocoon, shaped very much like the grass hammocks made by the natives of tropical America, and bearing a considerable resemblance to them in general form, as well as in the loose and open meshes. So long, indeed, are the meshes made, that the inclosed insect can be seen through the network, from the time that the old wrinkled skin is cast off and pushed away in a heap by the white and shining chrysalis, to the time when the chrysalis shell is in its turn shattered, and the perfect moth creeps slowly into the air, all dull, and sodden, and bewildered, with its undeveloped wings looking like four mottled split peas rather than the beautiful members which they soon become, when the air has passed into their vessels, and their multitudinous folds have been shaken out.

I hope that none of my readers will kill a Tiger Moth in either of its stages. It does no harm to the gardener, and has quite enough foes of its own; the ichneumon flies piercing it in spite of its long bristles, and the cuckoo, together with other birds, reveling in so large and juicy a morsel. It is a special favorite of mine, this great moth, for I have kept so many hundreds of them, and have admired the wondrous details of their anatomy so often, that I am always glad to say a kind word for a creature which has afforded me so much amusement and instruction.

Among the pensile insects may be reckoned the beautiful BURNET MOTH (Anthrocera filipendulæ), an insect which has already been mentioned while treating of the pensile hymenoptera.

This insect, which is well known for its splendid colors of deep velvet green and blazing scarlet, is also notable for the shape of its antennæ, which are so swollen toward the tips as to induce many persons to reckon the insect as a butterfly rather than a moth.

The shape of the cocoon of the Burnet Moth is not unlike that of the Tiger Moth, but its material and position are very different. The cocoon of the tiger moth is slung horizontally, in hammock fashion, while that of the Burnet is set perpendicularly, and fastened to the upper part of a grass stem, one side being firmly pressed against it. The substance of the cocoon is quite opaque, grayish, rather stout, very tough, and having the silken threads, of which it is chiefly made, so conspicuous, that many persons take the cocoon to be the work of a spider.

Sometimes in a field, or even in a limited portion of a field, these cocoons are so numerous that, at a little distance, they look almost as if they were the seeds of a plant rather than the cocoons of an insect. In such cases the moths themselves may generally be found near the cocoons, sometimes being on the ground and sometimes on the wing. These moths are peculiarly liable to the attacks of the ichneumon flies, for not only does the Burnet ichneumon make them its special prey, but I have seen a large percentage of the cocoons bored full of holes, which show that one of the parasitic hymenopteræ has laid its eggs in the caterpillar; that the young have been developed, and made their escape to continue the work of destruction; and that the caterpillar which nurtured them is lying dead within its useless cocoon.

THERE are others of our finest and yet commonest moths which make to themselves pensile habitations in which they pass the long time of helplessness when they are in the pupal state. Any thing more utterly helpless than the pupa of certain moths can not well be imagined, their only protection consisting either in their hiding-place or the sheltering armor in which the creature is enveloped.

The fur-clad DRINKER MOTH, for example (Odonestis potatoria), spins a cocoon which bears some resemblance in its texture to that of the Burnet Moth, though it is rather looser in structure and is of much larger dimensions. The general color of the cocoon is gray, with a few brownish mottlings here and there, and in form it is spindle-shaped, being widest in the centre, and diminishing to a point at either extremity. Conspicuous as this cocoon appears to be when exhibited in a glass case, it is any thing but conspicuous in the position wherein it is placed by the insect. I have bred at least two hundred moths from the caterpillar, and though the space was necessarily limited, many of the cocoons escaped observation until after the moth had been developed and made its escape.

Like the Burnet Moth, the Drinker is very liable to the attacks of ichneumons. There is now before me a cocoon which was made in 1846, and is preserved as one of the first instances of an entomologist's disappointment. As it now lies on its slab of white cardboard, it looks as if a charge of dust-shot had been fired through it, no less than seventeen minute holes being perceptible on one side alone, each hole representing at least one ichneumon fly which had made its escape after fulfilling its destructive mission.

THE handsome OAK-EGGER MOTH (Gastropacha quercus) affords another example of the pensile cocoon. Of these insects also I have had great numbers; and some specimens of the moth, chrysalis, and cocoon are now before me, the cocoon unchanged by the eighteen years which have elapsed since it was made, but the moth sadly faded, after the manner of its kind when exposed to the action of light. This insect, by the way, is one of those which suffer the most from the fumes of sulphur, a lesson which I long ago learned from experience. Having been told that the best method of killing moths was to expose them to the fumes of burning sulphur, I invented an apparatus which would cause the insects to be enveloped in dense fumes, while the heat of the burning sulphur was carried off in another direction.

Of its efficacy as a means of destruction no complaint can be made, inasmuch as it destroyed the insect in a very few moments; but as it likewise discharged the colors, its use was soon given up.

All the beautiful scarlets lost their tone, and became pale orange, and in the case of the Oak-egger and similar moths, the warm dun of the wings changed to dirty yellow. Moreover, the sublimated sulphur was sure to rest upon the wings, and to destroy their delicacy.

Camphor, which is so largely and so wrongly used in cabinets, is liable to the same objection. Its volatility is extreme, a large lump vanishing in a wonderfully short time when exposed to the air. The pieces of camphor used in cabinets continually need renewal, and the question frequently arises, Where has the camphor gone? The answer may be found in the dimmed glass, on which a deposit has been left, and which is so difficult to be cleaned, as well as on the inclosed insects, the lustre of whose bodies is sadly marred by the same substance.

Large as is the caterpillar of the Oak-egger Moth, it is contracted into a comparatively small chrysalis when it assumes the pupal state, and makes a cocoon which only allows enough space for the pupa and the cast larval skin. The form of the cocoon is egg-shaped, whence the name of Oak-egger, and its substance is rather peculiar, being thin, hard, and rather brittle when quite dry. Externally it is surrounded by a loose layer of silken threads, by means of which it is attached to the plant on which it hangs, but the cocoon itself is smooth, very much the color of half-charred paper, and in spite of its brittleness is possessed of some elasticity.

The manner in which the insect packs itself in so narrow a cell is most ingenious, and a cocoon may well be sacrificed in order to show the method by which this feat is achieved. If a cocoon be opened longitudinally, the chrysalis will be seen to fill the whole of the interior. On examining it more closely, the cast skin is seen to envelop the whole abdomen of the pupa, being pushed down in folds so as to fit closely round the pointed abdomen, and to occupy as little space as possible.

When the moth escapes from the cocoon, it breaks away quite a large hole at the end next the head, and slips out of the chrysalis shell with great ease, by lifting up a large flap which covers the legs and the head, and which gives way at the line of demarcation which separates it from the wings. In consequence of this arrangement, the pupal shell and the cast caterpillar skin remain in exactly the same position, and by means of a little ingenuity the raised flap can be replaced and fastened so as to give no indications that the insect has ever broken it. These cocoons are far more conspicuous than those of the Drinker Moth, and are attached rather lightly to the stems of various plants.

There is a smaller insect, popularly called the LITTLE EGGER MOTH (Eriogaster lanestris), which spins a cocoon of a similar structure, except that the walls are of even harder and more uniform texture, scarcely larger than a wren's egg, and of a substance which looks almost as if it were made of the same material as the egg. When broken, it is found to be even more brittle than that of the larger insect. Owing, in all probability, to the exceeding closeness of the structure, which would exclude air from the inhabitant, it is perforated with one or two very tiny, and very circular holes, which look just as if some one had been trying to kill the insect by piercing the cocoon with a fine needle or pin.

Even from the outside these perforations are visible, but they are much more evident when the cocoon is opened. The object of these holes is, however, conjectural, and it would be a useful experiment to stop them with wax, in order to see whether the inclosed insect could be developed when the air was thus excluded. I believe that there are none of these holes in the cocoon of the large Oak-egger Moth, and if there be any such perforations, they are so minute as to escape notice.

IF the reader will refer to page 294, he will see an account of certain cocoons which are made by hymenopterous insects, and suspended by a single thread from the branches. In Mr. H. W. Bates's work on the natural history of the Amazon River, there is a most interesting account of a pensile cocoon also suspended by a single thread, but which is the work of a lepidopterous insect. It will be seen that Mr. Bates was able to see the insects spin the cocoon, and his account exactly tallies with Mr. Westwood's conjecture as to the method by which the creature manages to produce a hollow cocoon at the end of a single thread. Mr. Bates's account is as follows: