Insect life: Souvenirs of a naturalist

by Jean-Henri Fabre

First experiment.—A Sphex, dragging her prey, is at a few inches from her burrow. Without disturbing her I cut the antennæ of the ephippiger, which we already know serve as harness. Having [[168]]recovered from her astonishment at the sudden lightening of her load, the Sphex returns and unhesitatingly seizes the base of the antennæ, the short stumps not cut off. Very short they are—hardly a millimetre long; no matter, they suffice for the Sphex, who grips what remains of her ropes and drags anew. With many precautions not to hurt her, I cut off the two stumps, now level with the skull. Finding nothing to seize at the parts familiar to her, she takes hold on one side of one of the long palpi of her victim, and drags it, not at all put out by this modification in her style of harnessing herself. I leave her alone. The prey is got home and placed with its head to the mouth of the burrow. The Sphex enters to make a short inspection of the interior before proceeding to store provisions. Her tactics recall those of S. flavipennis in like circumstances. I profit by this brief moment to take the abandoned prey, deprive it of all its palpi, and place it a little farther off—a pace from the burrow. The Sphex reappears and goes straight to her game, which she saw from her threshold. She seeks above the head, she seeks below, on one side, and finds nothing to seize. A desperate attempt is made; opening wide her mandibles she tries to grasp the ephippiger by the head, but her pincers cannot surround anything so large, and slip off the round, polished skull. She tries several times in vain; at length, convinced of the futility of her efforts, draws back, and seems to renounce further attempts. She appears discouraged—at least she smooths her wings with her hind feet, while with her front tarsi, first passing them through her mouth, she washes her [[169]]eyes, a sign among Hymenoptera, as I believe, that they give a thing up.

Yet there were points by which the ephippiger might be seized and dragged as easily as by the antennæ and palpi. There are the six feet, there is the ovipositor—all organs slender enough to be thoroughly grasped and used as traction ropes. I own that the easiest way of getting the prey into the storehouse is to introduce it head first by the antennæ; yet, drawn by one foot, especially a front one, it would enter almost as easily, for the orifice is wide and the passage short, even if there be one. How came it then that the Sphex never once tried to seize one of the six tarsi or the point of the ovipositor, while she did make the impossible, absurd attempt to grip with mandibles far too short the huge head of her prey? Perhaps the idea did not occur to her. Let us try to suggest it. I place under her mandibles first a foot, then the end of the abdominal sabre. She refuses obstinately to bite; my repeated solicitations come to nothing. A very odd kind of hunter this to be so embarrassed by her game and unable to think of seizing it by a foot if it cannot be taken by the horns! Perhaps my presence and all these unusual events may have troubled her faculties; let us leave her to herself, with her burrow and ephippiger, and give her time to consider and to imagine in the calm of solitude some means of managing the business. I walked away and returned in a couple of hours to find the Sphex gone, the burrow open, and the ephippiger where I had laid it. The conclusion is that the Sphex tried nothing, but departed, abandoning home, [[170]]game—everything, when to utilise them all that was needed would have been to take the prey by one foot. Thus this rival of Flourens, who just now startled us by her science when pressing the brain to induce lethargy, is invariably dull when the least unusual event occurs. The Sphex, which knows so well how to reach the thoracic ganglia of a victim with her sting, and those of the brain with her mandibles, and which makes such a judicious difference between a poisoned sting that would destroy the vital influence of the nerves, and compression causing only momentary torpor, cannot seize her prey in a new way. To understand that a foot may be taken instead of the antennæ is impossible; nothing will do but the antennæ or another filament of the head or one of the palpi. For want of these ropes her whole race would perish, unable to surmount this trifling difficulty.

Second experiment.—The Sphex is busy closing her burrow where the prey is stored and the egg laid. With her fore tarsi she sweeps backward before her door, and launches from the entrance a spurt of dust, which passes beneath her, and springs up behind in a parabolic curve as continuous as if it were a slender stream of some liquid, so rapidly does she sweep. From time to time she chooses some sand grains with her mandibles, strengthening materials inserted singly in the dusty mass. To consolidate this she beats it with her head, and heaps it with her mandibles. Walled up by this masonry, the entrance rapidly disappears. In the midst of the work I intervene. Having put the Sphex aside I clear out the short gallery carefully with the blade [[171]]of a knife, take away the materials which block it, and entirely restore the communication of the cell with the outer air. Then, without injuring the edifice, I draw the ephippiger out of the cell where it is lying with its head to the far end, and its ovipositor to the entrance. The egg is as usual on its breast, near the base of one of the hind legs—a proof that the Sphex had given her last touch to the burrow, and would never return. These dispositions made, and the ephippiger placed safely in a box, I gave up my place to the Sphex, who had been watching while her domicile was rifled. Finding the entrance open, she entered and remained some moments, then came forth and took up her work where I interrupted it, beginning to stop the entrance conscientiously, sweeping the dust backward, and transporting sand grains to build them with minute care, as if doing a useful work. The orifice being again thoroughly blocked, she brushed herself, seemed to give a glance of satisfaction at her work, and finally flew off.

Yet she must have known that the burrow was empty, since she had gone inside, and made prolonged stay, but yet after this visit to the plundered dwelling, she set to work to close it with as much care as if nothing had happened. Did she propose to turn it later to account, returning with a fresh prey, and laying a new egg? In that case the burrow was closed to defend it from indiscreet visitors while the Sphex was away. Or it was a measure of prudence against other miners who might covet a ready-made chamber, or a wise precaution against internal wear and tear, and, in fact, [[172]]some predatory Hymenoptera are careful when obliged to suspend work to defend the mouth of their burrow by closing it up temporarily. I have seen certain Ammophilæ, whose burrow is a vertical well, close the entrance with a little flat stone when the insect goes a-hunting, or stops mining when the hour to leave off work comes at sunset. But in that case the stoppage is slight—a mere slab set on the top of the well. It takes but a moment when the insect comes to displace the little flat stone, and the door is open. But what we have just seen the Sphex construct is a solid barrier—strong masonry, where layers of alternate dust and gravel occupy the whole passage. It is definitive, and no temporary work, as is sufficiently shown by the careful way in which it is constructed. Besides, as I think I have already proved, it is very doubtful, considering the manner in which she acted, whether the Sphex would return to use the dwelling which she had prepared. A new ephippiger will be caught elsewhere, and elsewhere too will the storehouse destined for it be hollowed. As, however, these are but conclusions drawn by reasoning, let us consult experiment, more conclusive here than logic. I let nearly a week pass in order to allow the Sphex to return to the burrow so methodically closed, and use it if she liked for her nest-laying. Events answered to the logical deduction; the burrow was just as I had left it, well closed, but without food, egg, or larva. The demonstration was decisive; the Sphex had not returned.

Thus we see the plundered Sphex go into her house, pay a leisurely visit to the empty chamber, [[173]]and the next moment behave as if she had not perceived the absence of the big prey which a little while before had encumbered the cell. Did she not realise the absence of food and egg? Was she really so dull—she, so clear-sighted when playing the murderer—that the cell was empty? I dare not accuse her of such stupidity. She did perceive it. But why then that other piece of stupidity which made her close, and very conscientiously too, an empty chamber which she did not mean to store? It was useless—downright absurd—to do this, and yet she worked with as much zeal as if the future of the larva depended on it. The various instinctive actions of insects are then necessarily connected; since one thing has been done, such another must inevitably follow to complete the first, or prepare the way for the next, and the two acts are so necessarily linked that the first must cause the second, even when by some chance this last has become not only superfluous, but sometimes contrary to the creature’s interest. What object could there be in stopping a burrow now useless, since it no longer contained prey and egg, and which will remain useless, since the Sphex will not return to it? One can only explain this irrational proceeding by regarding it as the necessary consequence of preceding actions. In the normal state of things the Sphex hunts her prey, lays an egg, and closes the hole. The prey has been caught, the egg laid, and now comes the closing of the burrow, and the insect closes it without reflecting at all, or guessing the fruitlessness of her labour.

Third experiment.—To know all and nothing, [[174]]according as the conditions are normal or otherwise, is the strange antithesis presented by the insect. Other examples drawn from the Sphegidæ will confirm us in this proposition. Sphex albisecta attacks middle-sized Acridians, the various species scattered in the neighbourhood of her burrow all furnishing a tribute. From the abundance of these Acrididæ the chase is carried on near at hand. When the vertical well-like burrow is ready, the Sphex merely flies over the ground near, and espies an Acridian feeding in the sunshine. To pounce and sting while it struggles is done in a moment. After some fluttering of the wings, which unfold like carmine or azure fans, some moving of feet up and down, the victim becomes motionless. Next it must be got home by the Sphex on foot. She performs this toilsome operation as do her kindred, dragging her game between her feet, and holding one of the antennæ in her mandibles. If a grass thicket has to be traversed, she hops and flutters from blade to blade, keeping firm hold of her prey. When within a few feet of her dwelling she executes the same manœuvre as does S. occitanica, but without attaching the same importance to it, for sometimes she neglects it. The game is left on the road, and though no apparent danger threatens the dwelling, she hurries toward its mouth, and puts in her head repeatedly, or even partly enters, then returns to the Acridian, brings it nearer, and again leaves it to revisit her burrow, and so on several times, always with eager haste.

These repeated visits have sometimes annoying results. The victim, rashly abandoned on a slope, [[175]]rolls to the bottom, and when the Sphex returns and does not find it where she left it, she must hunt for it, sometimes in vain. If found, there will be a difficult climb, which, however, does not prevent her leaving it once more on the perilous slope. The first of these repeated visits to her cell is easily explained. Before bringing her heavy load she is anxious to make sure that the entrance is clear, and that nothing will hinder her carrying in the prey. But what is the use of her other visits, repeated so speedily one after another? Are the Sphex’s ideas so unstable that she forgets the one just made, and hurries back a moment later, only to forget that she has done so, and so on? It would indeed be a slippery memory where impressions vanished as soon as made. Let us leave this too obscure question.

At length the game is brought to the edge of the well, its antennæ hanging into the mouth, and there is an exact repetition of the method used by S. flavipennis, and, though in less striking conditions, by S. occitanica. She enters alone, reappears at the entrance, seizes the antennæ, and drags in the Acridian. While she was within I have pushed the prey rather farther off, and have always obtained precisely the same result as in the case of the huntress of crickets. In both Sphegidæ there was the same persistence in plunging into their burrows before dragging down their prey. We must recollect that S. flavipennis does not always allow herself to be duped by my trick of withdrawing the insect. There are elect tribes among them,—strong-minded families,—who after a [[176]]while find out the tricks of the experimenter, and know how to baffle them. But these revolutionaries capable of progress are the few; the rest, rigid conservatives in manners and customs, are the majority, the crowd. I cannot say whether the hunters of Acrididæ show more or less cunning in different districts.

But the most remarkable thing, and the one to which I want specially to come, is this. After withdrawing the prey of S. albisecta several times from the mouth of the hole, and obliging her to fetch it back, I profited by her descent to the bottom of her den to seize and put the prey where she could not find it. She came up, sought about for a long time, and, when quite convinced that it was not to be found, went down again. A few moments later she reappeared. Was it to return to the chase? Not the least in the world; she began to close the hole, and with no temporary cover, such as a small flat stone to mark the orifice, but with a solid mass of carefully collected dust and gravel swept into the passage until it was quite filled. S. albisecta only makes a single cell at the bottom of her well, and puts in but one victim. This one specimen had been caught and dragged to the edge of the hole, and if it was not stored, that was my fault, not her’s. The Sphex worked by an inflexible rule, and according to that rule she completed the work by stopping up the hole even if empty. Here we have an exact repetition of the useless labour of S. occitanica whose dwelling I rifled.

Fourth experiment.—It is almost impossible to [[177]]be certain whether S. flavipennis, which makes several calls at the bottom of the same passage, and heaps several grasshoppers in each, commits the same irrational mistakes when accidentally disturbed. A cell may be closed, although empty or imperfectly stored, and yet the Sphex will return to the same burrow to make others. Yet I have reason to believe that this Sphex is subject to the same aberrations as her two relations. The facts on which I base my belief are these. When the work is completed, there are generally four grasshoppers in each cell, but it is not uncommon to find three or only two. Four appears to me the usual number—first, because it is the most frequent, and secondly, when I have brought up young larvæ dug up when eating their first grasshopper, I found that all, even those only provided with two or three, easily finished those offered, up to four, but after that they hardly touched the fifth ration. If four grasshoppers are required by the larva to develop fully, why is it sometimes only provided with three or even only two? Why this immense difference in the amount of food? It cannot be from any difference in the joints served up, since all are unmistakably of the same size, but must come from losing prey on the road. In fact, one finds at the foot of the slopes whose upper parts are occupied by Sphegidæ, grasshoppers killed, and then lost down the incline, when, for some reason or other, the Sphex has momentarily left them. These grasshoppers become the prey of ants and flies, and the Sphex who finds them takes good care not to pick them up, as they would take enemies into the burrow. [[178]]