Ichneumonidae

“ Finally, it may not be a logical deduction, but to my imagination it is far more satisfactory to look at such instincts as the young cuckoo ejecting its foster-brothers, ants making slaves, the larvae of ichneumonidae feeding within the live bodies of caterpillars, not as specially endowed or created instincts, but as small consequences of one general law leading to the advancement of all organic beings—namely, multiply, vary, let the strongest live and the weakest die. ”

“ The Ichneumonidæ are a very numerous tribe, no fewer than 1300 European species having been described by Gravenhorst in his monograph of this family, and of these a large proportion occur in Britain. Our British species, however, have not yet been carefully investigated, and it is much to be desired that some competent observer would undertake the task. These insects perform an essential service by destroying so many caterpillars, which, if left to multiply unchecked, would totally consume many of our most useful plants. ”

“ This insect very closely resembles the common English species Ichneumon luteus, Linn. It is, however, considerably larger.
After describing this insect our author took occasion to enter into the natural history of the family to which it belongs, namely, the Ichneumonidæ, so named from the Linnæan genus Ichneumon, which last he says, "appears to be taken from its nature and way of life." He then proceeds as follows:—
"It is generally known that butterflies are produced from caterpillars, and that these caterpillars put on different forms before they arrive to that of the butterfly ”

“ I am extremely obliged to you for the Ichneumonidae which I shall place in my cabinet, 2 or 3 of these are valuable acquisitions and I will send you a few insects which I hope will prove acceptable. Will you be kind enough to look again at your Lucina fasciata for I fear it is not that genus and if not what is it? Dale and Walker were much pleased with their insects, I sent 20 species to the former and 11 to the latter Gent: and Mr. ”

“ The ichneumon tribe, one of Nature's greatest counterpoises to keep down the too rapid increase of the insect world, lay their eggs in the larvæ of other insects, which eggs when hatched develop into a devouring brood, which ungratefully turn upon and devour the helpless creature that sheltered them as a nest. The female ichneumon having discovered a caterpillar or grub which her instinct informs her has not been previously attacked, at once proceeds to thrust her ovipositor into the writhing body of her victim, depositing one or more eggs, according to the size of the living food-supply. ”

“ It is, however, doomed, and destined never to enter into the moth or butterfly state of existence. In due time the eggs are hatched by the warmth of its own body, and on this body to which they are so highly indebted, the young ichneumons, now in their own caterpillar state, begin with unconscious ingratitude to prey. They feast upon it day and night, but the creature, ordained by the iron laws of nature to suffer in this way, is long-lived, and though sickening from day to day, has often sufficient strength to become full-fed, and make its cocoon, and pass into the chrysalis, or pupal, state. ”

“ The ichneumon shows rare intelligence, inasmuch as she invariably deposits her eggs on the young members—the calves, as it were—of the herd; she seems to know that the older aphides would die before the ichneumon grubs arrived at a suitable age for pupation; hence she selects the young ones. She runs here and there about the colony until she finds a young aphis; then, curving her abdomen between her legs, she will quickly lay an egg on the body of the unconscious insect. ”

“ The deadliest foe of the Puss Moth larva, however, is the ichneumon-fly, a parasitic [Pg 156] creature, which lays its eggs in living caterpillars, and lets its grubs hatch out inside them, so as to devour the host from within in the most ruthless fashion. There are many kinds of ichneumon-fly, some of them very minute: the one which attacks the Puss Moth in its larval stage is a comparatively big one. The fly lays its eggs behind the caterpillar's head, where the victim is powerless to dislodge them. ”

“ To be a withered leaf is my first line of defence; if the ichneumon buzzes [Pg 216] nearer, I shift my ground and become a spider. I am the only caterpillar in the country with spider-legs; when they are stretched to their full length and quivering, they are worse to look at than the real thing. Should even [Pg 217] this fail me, I show the imitation scar on my fourth body-ring. That usually clinches the matter. The ichneumon fondly imagines that I am already occupied. So, if I am lucky, I turn at length to dingy pupa, and thus preserve my race.”
“Will you hear an amphibian?” said the toad. ”

“ You may always know an ichneumon-fly by its quivering antennæ; they are never still for a moment while daylight lasts, and the fly itself may also be known by its long, slender body with a hairlike waist. Some of the species are so minute that they lay several of their eggs within a butterfly’s egg, and it affords quite enough food for the ichneumon-grubs until they are full grown.
Others again are large insects with such a long and powerful tube that they can pierce through solid wood in order to reach the concealed grub in which they desire to lay their eggs. ”

“ Such are the Ichneumons, beautiful winged insects, which perfidiously insert their eggs in the body of a living caterpillar, whose internal part serves at the same time for a cradle and for food. The young larva devours organ after organ, beginning with the least important, till the last serves for the formation of the last members of the winged insect.
More unfortunate are those which are kept under the bolts and bars of their host from their early youth to mature age; they have no participation in the great banquet of life, except it be in the pleasures of the table and of love. ”

“ If some other ichneumon has preceded her, she recognizes the fact at once, and will not deposit her egg, but will go in search of another grub. When the egg is hatched, the larva feeds on the body of its host, carefully avoiding the vital organs. The caterpillar retains just enough vitality to assume the pupa state, and then dies. The chrysalis discloses, not a butterfly, but an ichneumon.
The mason wasp (Epipone spinipes) builds its cells and lays its eggs, one in each cell. It then hunts and procures spiders, which it deposits in the cells and then seals the openings. ”

“ The pupa may be frequently discovered inside that of the moth, and is quite white in its early stages, but as age advances all the colours of the future insect can be seen through the thin pellicle which invests it. The perfect insect makes its escape through a circular hole, which it drills in the upper end of the unfortunate moth pupa it has destroyed. The sexes of all ichneumon-flies may be at once recognized by the females possessing an ovipositor [3] differing considerably in length among the various species, but nearly always plainly visible. ”

“ These ichneumons discover with astonishing ingenuity the caterpillar which can bring up their young, and they often reach it with their ovipositor in the midst of a fruit, or in the substance of a branch of a tree. Every one knows the Anobium and other little beetles which attack wood, and live in the dark galleries which they excavate. The mother ichneumon knows perfectly how to discover the beetle which bores into our furniture, and winged ichneumons have often been seen to proceed from worm-eaten wood. It is not only caterpillars that are sought by ichneumons for the sake of their young ”

“ The ichneumon flies (of the order Hymenoptera) are four-winged, slender-bodied insects which lay their eggs either on or in (by means of a sharp piercing ovipositor) some caterpillar or beetle grub, into the body of which the young grub-like ichneumon larvæ burrow on hatching. The parasites feed on the body-tissues of the host, not attacking, however, such organs as the heart or nervous system, which would produce the immediate death of the host. The caterpillar lives with the ichneumon grubs within it usually until nearly time for its pupation. ”

“ The Ichneumon-flies are parasitic, their larvæ feed upon the substance of the Aphides. The genus Aphidius is particularly provided to furnish parasites to these insects, in which they deposit a single egg selecting a louse of the proper size to sustain their progeny: the egg hatches to a larva, which exhausts the Aphis by the time it has attained its growth, when the poor creature fastens itself securely to the leaf, and dies, leaving its carcase a secure resting place for the pupa of the Ichneumon. ”

“ The whole tribe of Ichneumon are celebrated for their courage; a small fly will not hesitate to attack the largest cockroach, who evinces the greatest terror at sight of his well-known enemy; but the greatest proof of valor in a fly is displayed in the war of the ichneumon against the spider.
There is a great variety of this insect in Ceylon, from the large black species, the size of the hornet down to the minute tinsel-green fly, no bigger than a gnat; but every one of these different species wages perpetual war against the arch enemy of flies. ”

“ What it is the animal has recourse to, never has been ascertained; of course, remains among our other important desiderata. The ichneumon is not only domesticated with facility, if obtained at an early age, but becomes extremely affectionate. Neither rats nor snakes will enter a house in which a tame ichneumon is retained, and allowed, as is usual, to range about at pleasure. The Saumpareahs, or snake-men, keep one, or more, for the purpose of exhibiting their feats in the attack of snakes. ”

“ The Indian ichneumon, a small creature, looking like both the weasel and the mongoose, is of great use to the natives because of its great hatred of snakes, which would otherwise make every footstep of the traveller most dangerous. This little creature, on seeing a snake, no matter how large, will instantly dart on it, and seize it by the throat, if he finds himself in an open place, where he has a chance of running to a certain herb, which he some way knows to be an antidote against the poison of the bite, if he should happen to receive one. ”

“ This Ichneumon Fly can, from outside, not only tell that inside the stem of that tree there is a caterpillar, but can locate the exact spot, and, still more wonderful, is able to determine whether or not that caterpillar is the particular species it is in search of. There are numerous other species of moths whose caterpillars feed in the centre of trees, and yet this female Ichneumon is able to mark down as her prey, although far out of reach of any sense known to us, that one species which alone can serve her purpose. ”

“ The slight puncture is scarcely felt by the grub, which continues to eat and grow; the inserted egg, however, presently hatches, and produces the ichneumon-grub, which begins to feed on the fat of the wasp-grub, instinctively avoiding the vital parts, until the latter has attained nearly its full size, and is ready to pass into the pupa state; when, its vigour being gone, it fails to accomplish the metamorphosis, the insidious intruder, now also full grown, taking its place, and by and by issuing from the hole a perfect Ichneumon. ”

“ A live larva has no odor. And, besides, the most difficult part is not to find out whether or not a suitably plump larva is there under the bark, at such and such a depth; it is also necessary to ascertain whether another ichneumon egg has not already been laid in the body of the coveted worm, as one larva would be insufficient for two nurslings. An egg deposited in some fat worm is not seen, heard, or felt; that is very evident. Nevertheless the ichneumon never plunges its terebra through the bark into a larva already occupied. ”

“ It then completes its own growth, pupates and eventually emerges as a very active, highly organized and beautifully colored fly, provided with a splendid nervous system, exquisite sense-organs and powerful locomotor organs in the shape of legs and wings. It is either a male or a female and, if of the latter sex, soon proceeds to place its offspring in immediate contact with the host. Although the larval Ichneumon exhibits modifications of structure almost as extreme as those of the adult Sacculina, these produce no effect on the organization of the adult insect. ”

“ It is of interest that the waters have been invaded by the parasitic group of the Hymenoptera, since in number of species this is by far the largest of the order. No group of terrestrial insects escapes their attacks—even larvae boring in wood are detected by ichneumon flies with excessively long ovipositors. Not a few cases are known in which a parasitic larva is itself pierced by the ovipositor of a “hyperparasite,” and even the offspring of the latter may itself fall a victim to the attack of a “tertiary parasite.” ”

“ The third larval form only a few live to reach. This is of the usual long, oval form of the larvæ of the ichneumons, and the body has thirteen segments exclusive of the head. The muscular system has greatly developed and the larva is much more lively in its motions than before. The new organs that develop are the air tubes and fat bodies. The "imaginal disks" or rudimentary portions destined to develop and form the skin of the adult, or imago, arise in the pupa state, which resembles that of other ichneumons. ”