We have now to consider the nature of the provisions placed by the Sphex near the egg. Each cell must contain four crickets. That is the amount of food necessary for a larva during its evolution, and these insects are in fact large enough to supply a considerable amount of nourishment. When the Sphex interrupts digging operations it is to fly on a hunting expedition. It soon returns with a cricket it has seized, holding it by one antenna which it turns round in its jaws. It is a heavy burden for the slender Sphex to bear. Sometimes on foot, dragging its burden after it, sometimes flying, and carrying the suspended cricket always in a passive condition, the burrow is gradually reached, not without difficulty. In spite of appearances, the cricket is not dead; it cannot move, but if kept for several days it will not putrefy, and its joints remain supple. It is simply the victim of a general paralysis.
The cause of the paralysis. — It was evidently of the greatest interest to know how the Sphex contrived this capture, and what method it used to suppress the movements of the prey. In order to obtain the solution of this problem, Fabre during a long period accumulated experiments and observations, and at last discovered in every detail how the thing was done. In order to compel the Sphex to act in his presence, he placed himself in front of the orifice of a gallery in which the insect was working; he soon saw it returning with a paralysed cricket. Arrived at the burrow, the insect placed the prey on the ground for a moment and disappeared in the passage to see that everything was in order, and that no damage had taken place since its departure. Everything was going well, and it reappeared, took up its burden, and again entered the subterranean passage, drawing the victim along. It brought it into the chamber for which it was destined, placing it on its back, the head down and the feet towards the door. Then it set out hunting again until it had ranged four crickets side by side. Before attempting a decisive experiment, the observer felt his way. At the moment when the Sphex was buried in the earth examining the chamber, Fabre withdrew the prey a short distance and awaited events. Having made the domiciliary visit, the Sphex then went straight to the place where it had left its insect, but could not find it. It was naturally very perplexed, and examined the neighbourhood with extreme agitation, not knowing what had happened, and evidently regarding the whole affair as very extraordinary; at last it found the victim it was seeking. The cricket still preserved the same immobility; its executioner seized it by an antenna and drew it anew to the entrance of the hole. In the interior of the subterranean domain everything is in good order; the insect had just assured itself of the fact, and we should expect to see it enter with its prey; not at all, it entered alone, and only decided to introduce the prey after it had made a fresh inspection. This fact is surprising, and it is still more surprising that if the practical joke of removing the cricket is repeated several times in succession, the Sphex drags it anew every time to the entrance of the burrow and first descends alone; forty times over this experiment succeeded without the insect deciding to renounce the habitual manœuvre. Fabre insists on this fact, and rightly, for nothing should be neglected; he makes it a text to show how automatic instinct is, and how the acts which proceed from it are invariably regulated so as to succeed one another always in the same order. In their nature these acts are quite indistinguishable from intelligent acts; only the creature is not capable of modifying them to bring them into harmony with unforeseen circumstances. All this is correct, but where it becomes excessive is in endowing animals alone with instinct and separating them from this point of view from Man. It is incontestable that the custom of visiting the burrow before introducing a victim into it has become so imperious in the Sphex that it cannot be broken, even when it is of no use. It is a mechanical instinct. But we may see an exactly parallel manifestation of human intelligence. In face of danger man utters cries of distress; they are heard and assistance comes. But these appeals are not intelligent and appropriate to the end; they are instinctive. Place the same individual in a situation where he knows very well that his voice cannot be heard; this will not hinder him from reproducing the same acts if he finds himself in the presence of danger. It is thus that the Sphex proceeds, guided by instincts, and it is no reason for despising it. And even in the course of this little experiment the insect gives proof of judgment. When it finds its cricket, it is perfectly aware that it is the same cricket which it brought, that there is no life in it, and that there is no need to re-commence the struggle; it sees too that it is not an ordinary corpse liable to putrefaction, but the very same cricket, and it does not hesitate to utilise it at once.
These habits being ascertained, Fabre proceeded to find out how the paralysis is produced. He awaited near a burrow the Sphex’s arrival, dragging a victim by an antenna, and while the insect was occupied in the subterranean survey he substituted a living cricket for that which the Sphex had left, expecting to find it on the spot where it had been placed. On emerging it perceives the cricket scampering away; not a moment was to be lost, and without reflection it leapt on the refractory victim. A lively struggle followed, a duel to the death among the blades of grass; it was a truly dramatic spectacle, the agile assailant whirling around the Cricket, who kicked violently with his hind legs. If a blow were to reach the Sphex it would be disembowelled; but it avoids the blows skilfully without ceasing its own violent attack. At last the combat ends; the cricket is brought to earth, turned on to its back, and maintained in this position by the Sphex. Still on its guard, the latter seizes in its jaws one of the filaments which terminate the abdomen of the vanquished, placing its legs on the belly; with the two posterior legs it holds the head turned back so as to stretch the under side of the neck. The cricket is unable to move and the conqueror’s sting wanders over the horny carapace seeking a joint, feeling for a soft place in which it can enter to give the finishing stroke. The dart at last reaches, between the head and the neck, the spot where the hard portions articulate, leaving between them a space without covering. The joint in the armour is found. The Sphex’s abdomen is agitated convulsively; the sting penetrates the skin, piercing a ganglion situated just beneath this point; the venom spreads and acts on the nervous cells, which can no longer convey messages to the muscles. That is not all; the sting wanders over the cricket’s belly, this time seeking the joint between the neck and the thorax; it finds it, and is again thrust in with fury; a second ganglion of the nervous chain is thus perforated and poisoned. After these two wounds the victim is completely paralysed.
As already mentioned, several facts enable us to recognise that the Cricket is by no means dead. It is simply incapable of movement, as would happen after an injection of curare. This poison kills a superior animal, for it hinders the muscular movements of the chest and diaphragm, necessary to respiration; but if a frog, which can breathe through its skin, is thus acted on it comes to life again at the end of twenty-four or forty-eight hours if the dose has not been too strong. The cricket is in a similar condition; it neither eats nor breathes; being incapable also of movement, there is no vital expenditure; it remains in a sort of torpor, or latent life, awaiting the tragic fate that is reserved for it. When it has been deposited in the little mortuary chamber the Sphex lays an egg on its thorax. The larva will soon come out to penetrate the body of the prey by enlarging the hole left by the sting. It thus finds for its first meals a food which unites the flavour of living flesh with the immobility of death. Nothing can be more convenient. When the first body is eaten it proceeds to the second, and thus devours successively the four victims stored up by maternal foresight.
In order not to interrupt the description and interfere with the succession of the acts, I have passed without remark the experiment in which Fabre substituted a living animal for the Sphex’s already paralysed captive. It seems to me, however, that in this circumstance the insect showed judgment, and knew how to act in accordance with new requirements. It was evidently the first time in insect memory in which so surprising a phenomenon had been seen as a victim at the last moment again taking the field. We cannot make instinct intervene here. If the Sphex’s acts are so automatic as we are sometimes led to believe, in accordance with facts which are perfectly accurate, we ought always to observe the following succession of acts: first, hollowing of the burrow; second, the chase; third, the blows of the dart; fourth, the different manœuvres for placing the victim in the sarcophagus. Now in the present case the insect had accomplished the first three series of actions, and had even begun the fourth; it ought next to drag the cricket into the burrow without listening to the recriminations which the latter had no business to make, since it was to be regarded as having received the two routine doses of poison. But the Sphex sees its victim come to life, understands this fact, and without seeking to fathom the cause judges that a new struggle and new blows of the sting are necessary; he understands that it is necessary to begin afresh, since the usual result has not been attained. He is then capable of reflection, and the series of acts which he accomplishes are not ordained with such inflexibility that it is impossible for him to modify them in order to conform them to varying circumstances.
The Sphex occitanica acts in the same manner as its relative in this complicated art of laying up provisions for the family. The differences are only in detail. Instead of hollowing the burrow first and then setting out on the chase to fill it, it does not devote itself to the labour of digging until a successful expedition has already assured the victim. ([Fig. 17.]) Instead of attacking crickets it seeks a larger orthopterous insect, the Ephippigera. The struggle is no doubt more difficult, but the result is proportionately greater, and the pursuit does not need to be so often renewed; a single captive is sufficient for its larva.[73]
The sureness of instinct. — It is not doubtful that a sure inherited instinct conducts the Sphex to prick its victim in the situation of the nervous ganglia, which will be wounded in the act. It may be said that the lesion results from the position in which the hymenopterous insect maintains its victim; for the sting is on the median line, and can only penetrate at the soft points; the two points attacked are then rigorously determined by physical circumstances. But these arguments have no bearing if we consider the method of procedure adopted by the Ammophila,[74] a hymenopterous insect related to the preceding, which paralyses caterpillars. It is free in this case to insert its sting at any portion of the body; yet it knows how to turn over and arrange the captive so that the dart shall penetrate both times at two points where ganglia will be poisoned and immobility without death be induced. It must then be agreed that there is here an instinct much too sure to be called mechanical; but these facts, which considered alone seem simply marvellous, become much less so, and lend themselves to evolutionary interpretation, when it is recognised that they are related by insensible degrees to other facts of the same order, much more intelligent and at the same time less sure.
Similar cases in which the specific instinct is less powerful and individual initiative greater. — Here is, for instance, the case of the Chlorion, where each animal possesses more considerable initiative.[75] It attacks the Cockroach. These insects are of an extremely varied size, according to age, and as they are also very agile the Chlorion is not certain of being always able to obtain victims of the same dimension. The orifice of its burrow, which it hollows in walls between the crevices of the stones, is calculated on the average size of its victims. It has also the habit of paralysing the cockroach by stinging it on the nervous chain. These preliminary operations do not impede it, but it is embarrassed when it wishes to introduce through the entrance of its gallery an insect which is too large. It pulls at first as much as it can, but seeing the failure of its efforts it does not persevere in this attempt, and comes out to survey the situation. Decidedly the victim is too large and cannot pass through. The Chlorion begins by cutting off the elytra, which maintain it rigid and prevent it from being compressed. This done, it harnesses itself anew and re-commences its efforts. But this is not sufficient, and the victim still resists. The insect returns, and again examines the situation. Now it is a leg which is placed cross-ways and opposes the introduction of the body; strong diseases need strong remedies, and our Chlorion sets itself to amputate this encumbering appendage. It triumphs at last; the cockroach yields to its efforts, and little by little penetrates the hole. As may be seen, the labour is laborious and painful, and may present itself beneath various aspects which call for a certain ingenuity on the part of the animal.