These beetles, however, in point of industry must yield the palm to one (Necrophorus Vespillo) whose singular history was first detailed by M. Gleditsch in the Acts of the Berlin Society for 1752. He begins by informing us that he had often remarked that dead moles when laid upon the ground, especially if upon loose earth, were almost sure to disappear in the course of two or three days, often of twelve hours. To ascertain the cause, he placed a mole upon one of the beds in his garden. It had vanished by the third morning; and on digging where it had been laid, he found it buried to the depth of three inches, and under it four beetles which seemed to have been the agents in this singular inhumation. Not perceiving any thing particular in the mole, he buried it again; and on examining it at the end of six days he found it swarming with maggots apparently the issue of the beetles, which M. Gleditsch now naturally concluded had buried the carcase for the food of their future young. To determine these points more clearly, he put four of these insects into a glass vessel half filled with earth and properly secured, and upon the surface of the earth two frogs. In less than twelve hours one of the frogs was interred by two of the beetles: the other two ran about the whole day as if busied in measuring the dimensions of the remaining corpse, which on the third day was also found buried. He then introduced a dead linnet. A pair of the beetles were soon engaged upon the bird. They began their operations by pushing out the earth from under the body so as to form a cavity for its reception; and it was curious to see the efforts which the beetles made by dragging at the feathers of the bird from below to pull it into its grave. The male having driven the female away continued the work alone for five hours. He lifted up the bird, changed its place, turned it and arranged it in the grave, and from time to time came out of the hole, mounted upon it and trod it under foot, and then retired below and pulled it down. At length, apparently wearied with this uninterrupted labour, it came forth and leaned its head upon the earth beside the bird without the smallest motion as if to rest itself, for a full hour, when it again crept under the earth. The next day in the morning the bird was an inch and a half under ground, and the trench remained open the whole day, the corpse seeming as if laid out upon a bier, surrounded with a rampart of mould. In the evening it had sunk half an inch lower, and in another day the work was completed and the bird covered.—M. Gleditsch continued to add other small dead animals, which were all sooner or later buried; and the result of his experiment was, that in fifty days four beetles had interred in the very small space of earth allotted to them, twelve carcases: viz. four frogs, three small birds, two fishes, one mole, and two grasshoppers, besides the entrails of a fish, and two morsels of the lungs of an ox. In another experiment a single beetle buried a mole forty times its own bulk and weight in two days[669]. It is plain that all this labour is incurred for the sake of placing in security the future young of these industrious insects along with a necessary provision of food. One mole would have sufficed a long time for the repast of the beetles themselves, and they could have more conveniently fed upon it above ground than below. But if they had left thus exposed the carcase in which their eggs were deposited, both would have been exposed to the imminent risk of being destroyed at a mouthful by the first fox or kite that chanced to espy them.
At the first view I dare say you feel almost inclined to pity the little animals doomed to exertions apparently so disproportioned to their size. You are ready to exclaim that the pains of so short an existence, engrossed with such arduous and incessant toil, must far outweigh the pleasures. Yet the inference would be altogether erroneous. What strikes us as wearisome toil, is to the little agents delightful occupation. The kind Author of their being has associated the performance of an essential duty with feelings evidently of the most pleasurable description; and, like the affectionate father whose love for his children sweetens the most painful labours, these little insects are never more happy than when thus actively engaged. "A bee," as Dr. Paley has well observed, "amongst the flowers in spring, (when it is occupied without intermission in collecting farina for its young or honey for its associates,) is one of the cheerfullest objects that can be looked upon. Its life appears to be all enjoyment: so busy and so pleased[670]."
Of the sources of exquisite gratification which every rural walk will open to you, while witnessing in the animals themselves those marks of affection for their unseen progeny of which I have endeavoured to give you a slight sketch, it will be none of the least fertile to examine the various and appropriate instruments with which insects have been furnished for the effective execution of their labours. The young of the saw-fly tribe (Serrifera[671]) are destined to feed upon the leaves of rose-trees and various other plants. Upon the branches of these the parent fly deposits her eggs in cells symmetrically arranged; and the instrument with which she forms them is a saw, somewhat like ours but far more ingenious and perfect, being toothed on each side, or rather consisting of two distinct saws, with their backs (the teeth or serratures of which are themselves often serrated, and the exterior flat sides scored and toothed), which play alternately; and, while their vertical effect is that of a saw, act laterally as a rasp. When by this alternate motion the incision, or cell, is made, the two saws, receding from each other, conduct the egg between them into it[672]. The Cicada, so celebrated by the poets of antiquity, which lays its eggs in dry wood, requires a stronger instrument of a different construction. Accordingly it is provided with an excellent double auger, the sides of which play alternately and parallel to each other, and bore a hole of the requisite depth in very hard substances without ever being displaced.
The construction of the sting or ovipositor with which the different species of Ichneumon are provided, is not less nicely adapted to its various purposes. In those which lay their eggs in the bodies of caterpillars that feed exposed on the leaves of plants it is short, often in very large species not the eighth of an inch long: having free access to their victims, a longer sting would have been useless. But a considerable number oviposit in larvæ which lie concealed where so short an instrument could not possibly approach them. In these, therefore, the sting is proportionably elongated, so much so that in some small species it is three or four times the length of the body. Thus in Pimpla Manifestator, whose economy has been so pleasingly illustrated by Mr. Marsham[673], and which attacks the larva of a wild bee (Chelostoma[674] maxillosa) lying at the bottom of deep holes in old wood, the sting is nearly two inches long[675]: and it is not much shorter in the more minute I. Strobilellæ L., which lays its eggs in larvæ concealed in the interior of fir cones, which without such an apparatus it would never be able to reach.
The tail of the females of many moths whose eggs require to be protected from too severe a cold and too strong a light, is furnished, evidently for application to this very purpose, with a thick tuft of hair. But how shall the moth detach this non-conducting material and arrange it upon her eggs? Her ovipositor is provided at the end with an instrument resembling a pair of pincers, which for this purpose are as good as hands. With these, having previously deposited her eggs upon a leaf she pulls off her tuft of hairs, with which she so closely envelops them as effectually to preserve them of the required temperature: and having performed this last duty to her progeny she expires.
The ovipositor of the capricorn beetles, an infinite host, is a flattened retractile tube, of a hard substance, by means of which it can introduce its eggs under the bark of timber, and so place them where its progeny will find their appropriate food[676]. The auger used by certain species of Œstrus, to enable them to penetrate the hides of oxen or deer and form a nidus for their eggs, has been before described[677].—But to enumerate all the varieties of these instruments would be endless.
The purpose which in the insects above mentioned is answered by their anal apparatus, is fulfilled in the numerous tribes of weevils by the long slender snout with which their head is provided. It is with this that Balaninus Nucum pierces the shell of the nut, and the weevil (Calandra granaria) the skin of the grains of wheat, in which they respectively deposit their eggs, prudently introducing one only into each nut or grain, which is sufficient, but not more than sufficient, for the nourishment of the grub that will inhabit it.
II. Hitherto I have adverted to those insects only which perish before their young come into existence, and can therefore evince their affection for them in no other way than by placing the eggs whence they are to spring in secure situations stored with food; and these include by far the largest portion of the race. A very considerable number, however, extend their cares much further: they not only watch over their eggs after depositing them, but attend upon their young, when excluded, with an affectionate assiduity equal to any thing exhibited amongst the larger animals, and in the highest degree interesting. Of this description are some solitary insects, as several species of the Linnean genus Sphex, earwigs, field-bugs, and spiders: and those insects which live in societies, namely, ants, bees, wasps, and termites: the most striking traits of whose history in these respects I shall endeavour to lay before you.
You have seen that the greater number of the Sphecina after depositing their eggs in cells stored with a supply of food, take no further care of them. Some, however, adopt a different procedure. One of these, called by Bonnet the Mason-wasp, but different from Reaumur's, not only incloses a living caterpillar along with its egg in the cell, which it carefully closes, but at the expiration of a few days, when the young grub has appeared and has consumed its provision, re-opens the nest, incloses a second caterpillar, and again shuts the mouth: and this operation it repeats until the young one has attained its full growth[678]. A similar mode, according to Rolander, is followed by Ammophila vulgaris as well as by the yellowish wasp of Pennsylvania, described by Bartram in the Philosophical Transactions[679], and by another related to Mellinus arvensis, observed by Duhamel[680]; both of which, however, instead of caterpillars, supply their larvæ with a periodical provision of living flies.
What a crowd of interesting reflections are these most singular facts calculated to excite! With what foresight must the parent insect be endowed, thus to be aware at what period her eggs will be hatched into grubs, and how long the provision she has laid up will suffice for their support! What an extent of judgement, thus in the midst of various other occupations to know the precise day when a repetition of her cares will be required! What an accuracy of memory, to recollect with such precision the entrance to her cell, which the most acute eye could not discover; and without compass or direction unerringly to fly to it, often from a great distance and after the most intricate and varied wanderings! If we refer the whole to instinct, and to instinct doubtless it must in the main if not wholly be referred, our admiration is not lessened. Instinct, when simple and directed to one object, is less astonishing; but such a complication of instincts, applied to actions so varied and dissimilar, is beyond our conception. We can but wonder and adore!