CHAPTER V.

MEANS OF DEFENCE OF THE LARVA.

There is, perhaps, no period in the life of an insect when it is so much in danger of the attacks of foes, as when it is in the larva state. Possessed, at the best, with but very feeble powers of locomotion, in comparison with those of winged insects, it is continually exposed to destruction on all sides, from which it has not the power to escape. Not only do insects of various species particularly select the larva for the object of their attacks, but birds and other creatures are also in the lists against them. Thus imperilled, what chance has the larva against foes so numerous, and in a contest so unequal? It has been calculated that a pair of sparrows, for their own consumption, and for that of their tender brood, destroy at least three thousand caterpillars in a week! and we well know what multitudes of larvæ fall into the clutches of the cawing rooks which follow the tail of the plough. The winged insects are tolerably secure, although many even of their ranks fall victims to the swift-winged swallow and sand-martin, and to the rapid leap of the artful trout. But the poor crawling larvæ are neither strong enough to fight, nor swift enough to flee, and fall by thousands into the unsparing hands of their various enemies.

Yet, the Creator, who has wisely appointed a large portion of their numbers for food to many creatures, has also taken many precautions to prevent their being entirely annihilated, as might otherwise have been the case. These are well deserving a brief notice, previous to our passing on to the last stage in the history of the larva. From what has been already said about the coats of various larvæ, it may be imagined that that must be a stout-hearted enemy which could venture to attack some of them. The spines and hard excrescences with which they are furnished must, undoubtedly, prove far from agreeable to the touch of a foe; and there can be no question that this sort of armour is, of itself, a good defence to many larvæ. Others form artificial coverings, which are equally useful, by concealing them from the notice of their enemies. Thus, as we have before remarked, some dwell in tubes of leaves, hid from every eye; others encase themselves in a shield of cemented gravel or shells, like those represented in the cut, presenting a most grotesque appearance; others hide themselves in variously-formed cells. Some, immediately on being touched, roll themselves up, like hedge-hogs, into a ball, which looks like a little globe of hairs, and is so slippery that it cannot be retained between the fingers; others, again, when they are touched, instantly drop down, and from their colour, resembling precisely that of the herbage into which they have fallen, it becomes next to fruitless to search for them.

A very singular larva which, both for offence and defence, adopts a most extraordinary procedure, must be mentioned by itself. This larva is not unfrequently to be found in our houses, and is said to feed upon our disgusting and annoying invaders--the bugs; but it so completely contrives to conceal its real character, that not once in a hundred times would it, probably, be recognised as an insect at all. It collects together a number of particles of sand, or fragments of wool, or silk, or earth, and with singular skill, contrives to form a sort of coat out of these, in which it envelopes itself. Thus attired, as may be imagined, it is not easy to discover what the object really is, and it thus, undoubtedly, escapes the undesirable notice of any of its enemies. But more than this: like those North American Indians, who hunt by concealing themselves in the skins of wolves, and so attract less attention from the herd than they would do if they were to expose themselves in their natural aspect to view, this crafty larva steals upon its prey in much the same manner, although it can run with sufficient swiftness when necessary. It creeps forward with the greatest stealth, moving only one leg at a time, and thus quite insensibly approaches its victim, who is not at all alarmed at what merely appears to be a lump of dust. Soon, however, it is convinced of its fatal mistake, and discovers the terrible fact that it is in the embrace of an unsparing devourer.

Other larvæ escape notice in a singular manner, by their close resemblance to little pieces of stick. Thus, we are told by Messrs. Kirby and Spence, that "there is a certain tribe of caterpillars called surveyors (_Geometræ_), that will sometimes support themselves, for whole hours, by means of their posterior legs, solely upon their hinder extremity, forming an angle, of various degrees, with the branch on which they are standing, and looking like one of its twigs. The body is kept stiff and immovable, with the separations of the segments scarcely visible; it terminates in a knob, the legs being applied close, so as to resemble a bud at the end of a twig; besides which, it often exhibits intermediate tubercles, which increase the resemblance. Its colour, too, is usually obscure, and similar to that of the bark of a tree: so that, doubtless, the sparrows and other birds are frequently deceived by this manoeuvre, and thus balked of their prey. Rösel's gardener, mistaking one of these caterpillars for a dead twig, started back in great alarm, when, upon attempting to break it off, he found it was a living animal."

Some, however, are actually armed, so as to offer an active resistance to the onslaught of any enemy. Mr. Abbot has described a terrible caterpillar, well known in certain districts in America, under the strange title of the "Hickory-horned Devil." This creature is furnished with seven or eight strong horn-like spines, upwards of half an inch in length, which project from its head and anterior segments. When threatened by danger, the caterpillar does not attempt to fly, but lifts up its head menacingly, and shakes it about in a very fierce manner. The negroes, in particular, are so terrified at its aspect, that they dread it as much as the rattlesnake. But, in reality, it is harmless; and Mr. Abbot, in order to convince the ignorant people that such was the case, took hold of it, in their presence, without receiving any injury. This, however, did not convince them, and they made answer that, although it did not sting him, it would undoubtedly sting them.

The weapon of another is thus pleasantly described by De Geer:--"In the month of July, I found a caterpillar resting upon a small twig, which I cut off in order to enable me to examine it more attentively. As I was scrutinizing its appearance, I happened, accidentally, to touch its body. Instantly there shot out, from a spot near the head, two streams of clear fluid, which struck me on the face, and partly entered one of my eyes, causing a very acute, but fortunately, not a very enduring pain. My surprise at this salute prevented my taking particular notice of the place from whence the jets proceeded. It appears probable that this caterpillar has been thus endowed with this squirting apparatus to enable it to defend itself against its enemies, or at least, to assist in frightening, or perhaps in hunting, its prey. For myself, I confess, after the reception I had met with, I felt some degree of fear at too nearly approaching it."

On examining them carefully at another opportunity, this entomologist found that these caterpillars were provided with a squirting apparatus, situated in a cleft in the neck. When the creature is irritated, it thrusts out a curious organ, divided into four branches, and drilled with holes, like the rose of a watering-pot. From this organ shoot the jets of fluid spoken of. After the discharge they are drawn in again, and covered over by the closing up of the cleft. Strange to say, when taken in-doors, the caterpillar lost the power of squirting altogether. It appeared as if it could only do so in the open air, where a number of insect enemies were arrayed against it. This caterpillar is commonly known as that of the Puss-moth, and has sometimes caused the most strange and foolish country tales by its striking appearance. It has been described as a horrible monster, having a head like a lion, jaws like a shark, a horn like a unicorn, and two tremendous stings in its tail! Certainly, its appearance is not the most engaging in the world, as may be conceived from the representation of it in the cut; and what adds to its singularity is, that it possesses the power of lashing its sides with its tail, so as to drive away flies. If the reader should be fortunate enough to find one, he may have some amusement in examining all the curious apparatus with which this rather forbidding looking insect is supplied.

The winter draws near, and sends its foretokening cold breathings to warn every creature, vegetable and animal, that the dark season is arriving, when food is no longer to be obtained. What is to become of the larva? Can it endure the penetrating tooth of frost, or the overwhelming shower of rain? Or can it endure to be from week to week, from month to month, without a mouthful of food? From the facts already stated with reference to the age of larva, it is very certain that many larvæ have to bear these trials; and some, not merely during one, but during several winters. We must, therefore, inquire how they have been defended, or strengthened, so as to enable them so to do.

The alteration in the coats of animals during winter, or rather, just previous to it, and the fact that animals destined to inhabit the arctic regions are enveloped in coats of the shaggiest hair, are well known to every person. There can be no doubt, that in many instances in the insect world, where a larva has to be exposed to the frosts of winter, the same provision of a hairy covering, which has been given to them by the Creator, is intended to meet the same end, and to preserve their soft and tender bodies from the destructive influence of extreme cold. The following striking observation of a talented entomologist, who has not thought it beneath him to write a most interesting book only on the family of ants (M. Huber), shows very clearly that such is, in fact, the intention of providing the larva with a covering of this kind. He noticed that the larvæ of some species of ants destined to pass through the winter, were furnished with this kind of warm clothing, while those which were not so destined had smooth coats, that is, even in the same species: thus proving to us, beyond a doubt, that as the winter approached, the warm coat was put on by the larvæ. The engraving on the last page represents some extraordinary specimens of hairiness in caterpillars from Brazil, now in the British Museum.

A large number of larvæ become torpid during winter--they are not dead--they are not sensibly alive--they are plunged in that long half-death which affects not only them but also many large animals, who retire in winter, lie down to sleep for weeks, and awake to find the cold departing, and the spring-time nigh at hand. But the frost sometimes proves too severe for them, and the poor insects become sometimes congealed into solid lumps of ice! Alas! we shall exclaim, then there is an end to their life when that takes place; and, undoubtedly, the severity of such a degree of cold destroys large numbers; yet, strange to say, some larvæ actually revive, even after they have been thus frozen into hard inanimate lumps. One observer states that he has found them in this condition; and so entirely congealed, that they chinked like small stones when dropped into a glass tumbler! yet they revived after careful management. In an experiment made during Sir John Ross's voyage to the arctic regions, upon the larvæ of a moth, they were four successive times exposed to the intense cold of 40° below zero, and four times they revived again on being brought into the warm atmosphere of the cabin. Experiments have also been made by other persons with a like result. It may, therefore, be considered certain that some larvæ will bear to be frozen into solid masses, so that they will snap asunder like an icicle, and yet return to life again; and even go through all their stages of development, into the perfect insect. How remarkable a fact this is, when we remember the deadly effect of frost upon man and the higher animals!

Many larvæ, however, form nests of various kinds, in which they comfortably spend the dreary days and nights of this stern season. "With this view," write the excellent observers, Kirby and Spence, "the larva of _Cossus ligniperda_ forms a covering of pieces of wood, lined with fine silk; those of some other moths excavate, under a stone, a cavity exactly the size of their bodies, to which they give all round a coating of silk; and the larvæ of _Pieris Cratægi_ enclose themselves, in autumn, in cases of the same material, and thus pass the cold season, in small societies of from two to twelve, under a common covering formed of leaves. Bonnet mentions a trait of the cleanliness of these insects, which is almost ludicrous. He observed in one of these nests a sort of sack, containing nothing but grains of excrement; and a friend assured him that he had seen one of these caterpillars partly protrude itself out of the case, the hind feet first, to eject a similar grain; so that it would seem the society have on their establishment a scavenger, whose business it is to sweep the streets, and convey the rejected matters to one grand repository. This, however singular, is rendered not improbable, from the fact that beavers dig, in their habitations, holes solely destined for a like purpose, as do also badgers."

A singular variety of larva-nest is mentioned by a Mexican traveller. He says,--"After having ascended for about an hour, we came to the region of oaks, and other majestically tall trees, the names of which I could not learn. Suspended from their stately branches were innumerable nests, enclosed, apparently, in white paper bags, in the manner of bunches of grapes in England, to preserve them from birds and flies. I had the curiosity to examine one of them, which I found to contain numberless caterpillars. The texture is so strong that it is not easily torn; and the interior contained a quantity of green leaves to support the numerous progeny within."

The larvæ of some Australian insects form the most curious nests we have ever beheld. A representation, taken from specimens in the entomological collection at the British Museum, will show what extraordinary structures these are. They appear like minute bundles of faggots, and have been formed by the insect cutting short pieces of twigs, all nearly of the same size, and then cementing them together in the manner represented. Some of these are of a large size, as large as a moderate-sized pear; others are smaller, and these present the most beautifully regular appearance, consisting of a number of very small rods, bound together in a cylindrical form, like the _fasces_ of the Roman soldiery.

In this manner larvæ pass through the winter. Without a doubt many perish; but there remain infinite numbers at the end of this season, which, from the depths of their cells, become sensible to the influence of spring, so soon as the first footsteps of that season are felt upon the earth. The larva wakens to active life once more; and with an appetite rendered all the keener by its fast of four or five months, it leaves its dormitory, and begins to consume whatever suitable food may lie in its way; and so it continues, until the time of its change approaches.