More Hunting Wasps Part 12

The choice is soon made: the Banded Epeira is the one preferred. But she does not yield without protest. On the approach of the Wasp, she rises and a.s.sumes a defensive att.i.tude, just like that of the Lycosa. The Calicurgus pays no attention to threats: under her harlequin's coat, she is violent in attack and quick on her legs. There is a rapid exchange of fisticuffs; and the Epeira lies overturned on her back. The Pompilus is on top of her, belly to belly, head to head; with her legs she masters the Spider's legs; with her mandibles she grips the cephalothorax. She curves her abdomen, bringing the tip of it beneath her; she draws her sting and...

One moment, reader, if you please. Where is the sting about to strike?

From what we have learnt from the other paralysers, it will be driven into the breast, to suppress the movement of the legs. That is your opinion; it was also mine. Well, without blushing too deeply at our common and very excusable error, let us confess that the insect knows better than we do. It knows how to a.s.sure success by a preparatory manoeuvre of which you and I had never dreamt. Ah, what a school is that of the animals! Is it not true that, before striking the adversary, you should take care not to get wounded yourself? The Harlequin Pompilus does not disregard this counsel of prudence. The Epeira carries beneath her throat two sharp daggers, with a drop of poison at their points; the Calicurgus is lost if the Spider bites her. Nevertheless, her anaesthetizing demands perfect steadiness of the lancet. What is to be done in the face of this danger which might disconcert the most practised surgeon? The patient must first be disarmed and then operated on.

And in fact the Calicurgus' sting, aimed from back to front, is driven into the Epeira's mouth, with minute precautions and marked persistency.

On the instant, the poison-fangs close lifelessly and the formidable quarry is powerless to harm. The Wasp's abdomen then extends its arc and drives the needle behind the fourth pair of legs, on the median line, almost at the junction of the belly and the cephalothorax. At this point the skin is finer and more easily penetrable than elsewhere. The remainder of the thoracic surface is covered with a tough breast-plate which the sting would perhaps fail to perforate. The nerve-centres, the source of the leg-movements, are situated a little above the wounded point, but the back-to-front direction of the sting makes it possible to reach them. This last wound results in the paralysis of all the eight legs at once.

To enlarge upon it further would detract from the eloquence of this performance. First of all, to safeguard the operator, a stab in the mouth, that point so terribly armed, the most formidable of all; then, to safeguard the larva, a second stab in the nerve-centres of the thorax, to suppress the power of movement. I certainly suspected that the slayers of robust Spiders were endowed with special talents; but I was far from expecting their bold logic, which disarms before it paralyses. So the Tarantula-huntress must behave, who, under my bell-gla.s.ses, refused to surrender her secret. I now know what her method is; it has been divulged by a colleague. She throws the terrible Lycosa upon her back, p.r.i.c.ks her p.r.i.c.kers by stinging her in the mouth and then, in comfort, with a single thrust of the lancet, obtains paralysis of the legs.

I examine the Epeira immediately after the operation and the Tarantula when the Calicurgus is dragging her by one leg to her burrow, at the foot of some wall. For a little while longer, a minute at most, the Epeira convulsively moves her legs. So long as these throes continue, the Pompilus does not release her prey. She seems to watch the progress of the paralysis. With the tips of her mandibles she explores the Spider's mouth several times over, as though to ascertain if the poison-fangs are really innocuous. When all movement subsides, the Pompilus makes ready to drag her prey elsewhere. It is then I take charge of it.

What strikes me more than anything else is the absolute inertia of the fangs, which I tickle with a straw without succeeding in rousing them from their torpor. The palpi, on the other hand, their immediate neighbours, wave at the least touch. The Epeira is placed in safety, in a flask, and undergoes a fresh examination a week later. Irritability has in part returned. Under the stimulus of a straw, I see her legs move a little, especially the lower joints, the tibiae and tarsi. The palpi are even more irritable and mobile. These different movements, however, are lacking in vigour and coordination; and the Spider cannot employ them to turn over, much less to escape. As for the poison-fangs, I stimulate them in vain: I cannot get them to open or even to stir. They are therefore profoundly paralysed and in a special manner. The peculiar insistence of the sting when the mouth was stabbed told me as much in the beginning.

At the end of September, almost a month after the operation, the Epeira is in the same condition, neither dead nor alive: the palpi still quiver when touched with a straw, but nothing else moves. At length, after six or seven weeks' lethargy, real death supervenes, together with its comrade, putrefaction.

The Tarantula of the Ringed Calicurgus, as I take her from the owner at the moment of transportation, presents the same peculiarities. The poison-fangs are no longer irritable when tickled with my straw: a fresh proof, added to those of a.n.a.logy, to show that the Lycosa, like the Epeira, has been stung in the mouth. The palpi, on the other hand, are and will be for weeks highly irritable and mobile. I wish to emphasise this point, the importance of which will be recognized presently.

I found it impossible to provoke a second attack from my Harlequin Calicurgus: the tedium of captivity did not favour the exercise of her talents. Moreover, the Epeira sometimes had something to do with her refusals; a certain ruse de guerre which was twice employed before my eyes may well have baffled the aggressor. Let me describe the incident, if only to increase our respect a little for these foolish Spiders, who are provided with perfected weapons and do not dare to make use of them against the weaker but bolder a.s.sailant.

The Epeira occupies the wall of the wire-gauze cage, with her eight legs wide-spread upon the trelliswork; the Calicurgus is wheeling round the top of the dome. Seized with panic at the sight of the approaching enemy, the Spider drops to the ground, with her belly upwards and her legs gathered together. The other dashes forward, clasps her round the body, explores her and prepares to sting her in the mouth. But she does not bare her weapon. I see her bending attentively over the poisoned fangs, as though to investigate their terrible mechanism; she then goes away. The Spider is still motionless, so much so that I really believe her dead, paralysed unknown to me, at a moment when I was not looking.

I take her from the cage to examine her comfortably. No sooner is she placed on the table than behold, she comes to life again and promptly scampers off! The cunning creature was shamming death beneath the Wasp's stiletto, so artfully that I was taken in. She deceived an enemy more cunning than myself, the Pompilus, who inspected her very closely and took her for a corpse unworthy of her dagger. Perhaps the simple creature, like the Bear in the fable of old, already noticed the smell of high meat.

This ruse, if ruse it be, appears to me more often than not to turn to the disadvantage of the Spider, whether Tarantula, Epeira or another.

The Calicurgus who has just put the Spider on her back after a brisk fight knows quite well that her prostrate foe is not dead. The latter, thinking to protect itself, simulates the inertia of a corpse; the a.s.sailant profits by this to deliver her most perilous blow, the stab in the mouth. Were the fangs, each tipped with its drop of poison, to open then; were they to snap, to give a desperate bite, the Pompilus would not dare to expose the tip of her abdomen to their deadly scratch. The shamming of death is exactly what enables the huntress to succeed in her dangerous operation. They say, O guileless Epeirae, that the struggle for life has taught you to adopt this inert att.i.tude for purposes of defence. Well, the struggle for life was a very bad counsellor. Trust rather to common sense and learn, by degrees, at your own cost, that to hit back, above all if you can do so promptly, is still the best way to intimidate the enemy. (Fabre does not believe in the actual shamming of death by animals. Cf. "The Glow-worm and Other Beetles," by J.

Henri Fabre, translated by Alexander Teixeira de Mattos: chapters 8 to 15.--Translator's Note.)

The remainder of my observations on these insects under gla.s.s is little more than a long series of failures. Of two operators on Weevils, one, the Sandy Cerceris (C. arenaria), persistently scorned the victims offered; the other, Ferrero's Cerceris (C. Ferreri), allowed herself to be empted after two days' captivity. Her tactical method, as I expected, is precisely that of the Cleonus-huntress, the Great Cerceris, with whom my investigations commenced. When confronted with the Acorn-weevil, she seizes the insect by the snout, which is immensely long and shaped like a pipe-stem, and plants her sting in its body to the rear of the prothorax, between the first and second pair of legs. It is needless to insist: the spoiler of the Cleoni has taught us enough about this mode of operation and its results.

None of the Bembex-wasps, whether chosen among the huntresses of the Gadfly or among the lovers of the House-fly rabble, satisfied my aspirations. Their method is as unknown to me now as at the distant period when I used to watch it in the Bois des Issards. (Cf. "The Hunting Wasps": chapters 14 to 18.--Translator's Note.) Their impetuous flight, their love of long journeys are incompatible with captivity.

Stunned by colliding with the walls of their gla.s.s or wire-gauze prison, they all perish within twenty-four hours. Swifter in their movements and apparently satisfied with their honeyed thistle-heads, the Spheges, huntresses of Crickets or Ephippigers, die as quickly of nostalgia. All I offer them leaves them indifferent.

Nor can I get anything out of the Eumenes, notably the biggest of them, the builder of gravel cupolas, Amedeus' Eumenes. All the Pompili, except the Harlequin Calicurgus, refuse my Spiders. The Palarus, who preys upon an indefinite number of the Hymenopteron clan, refuses to tell me if she drinks the honey of the Bees, as does the Philanthus, or if she lets the others go without manipulating them to make them disgorge. The Tachytes do not vouchsafe their Locusts a glance; Stizus ruficornis promptly gives up the ghost, disdaining the Praying Mantis which I provide for her.

What is the use of continuing this list of checks? The rule may be gathered from these few examples: occasional successes and many failures. What can be the reason? With the exception of the Philanthus, tempted from time to time by a b.u.mper of honey, the predatory Wasps do not hunt on their own account; they have their victualling-time, when the egg-laying is imminent, when the family calls for food. Outside these periods, the finest heads of game might well leave these nectar-bibbers indifferent. I am careful therefore, as far as possible, to capture my subjects at the proper season; I give preference to mothers caught upon the threshold of the burrow with their prey between their legs. This diligence of mine by no means always succeeds. There are demoralized insects which, once under gla.s.s, even after a brief delay, no longer care about the equivalent of their prize.

All the species do not perhaps pursue their game with the same ardour; mood and temperament are more variable even than conformation. To these factors, which are of the nicest order, we may add that of the hour, which is often unfavourable when the subject is caught at haphazard on the flowers, and we shall have more than enough to explain the frequency of the failures. After all, I must beware of representing my failures as the rule: what does not succeed one day may very well succeed another day, under different conditions. With perseverance and a little skill, any one who cares to continue these interesting studies will, I am sure, fill up many gaps. The problem is difficult but not impossible.

I will not quit my bell-jars without saying a word on the entomological tact of the captives when they decide to attack. One of the pluckiest of my subjects, the Hairy Ammophila, was not always provided with the hereditary dish of her family, the Grey Worm. I offered her indiscriminately any bare-skinned caterpillars that I chanced to find.

Some were yellow, some green, some brown with white edges. All were accepted without hesitation, provided that they were of suitable size.

Tasty game was recognized wonderfully under very dissimilar liveries.

But a young Zeuzera-caterpillar, dug out of the branches of a lilac-tree, and a silkworm of small dimensions were definitely refused.

The over-fed products of our silkworm-nurseries and the mystery-loving caterpillar which gnaws the inner wood of the lilac inspired her with suspicion and disgust, despite their bare skin, which favoured the sting, and their shape, which was similar to that of the victims accepted.

Another ardent huntress, the Interrupted Scolia, refused the Cetonia-grub, which is of like habits with the Anoxia-larva; the Two-banded Scolia also refused the Anoxia. The Philanthus, the headlong murderess of Bees, saw through my trickery when I confronted her with the Virgilian Bee, the Eristalis (E. tenax). She, a Philanthus, take this Fly for a Bee! What next! The popular idea is mistaken; antiquity too is mistaken, as witness the "Georgics," which make the putrid remains of a sacrificed Bull give birth to a swarm; but the Wasp makes no mistake. In her eyes, which see farther than ours, the Eristalis is an odious Dipteron, a lover of corruption, and nothing more.

CHAPTER 14. OBJECTIONS AND REJOINDERS.

No idea of any scope can begin its soaring flight but straightway the curmudgeons are after it, eager to break its wings and to stamp the wounded thing under foot. My discovery of the surgical methods that give the Hunting Wasps their preserved foodstuffs has undergone the common rule. Let theories be discussed, by all means: the realm of the imagination is an untilled domain, in which every one is free to plant his own conceptions. But realities are not open to discussion. It is a bad policy to deny facts with no more authority than one's wish to find them untrue. No one that I know of has impugned by contrary observations what I have so long been saying about the anatomical instinct of the Wasps that hunt their prey; instead, I am met with arguments. Mercy on us! First use your eyes and then you shall have leave to argue! And, to persuade people to use their eyes, I mean to reply, since we have time to spare, to the objections which have been or may be raised. Of course, I pa.s.s over in silence those in which childish disparagement shows its nose too plainly.

The sting, I am told, is directed at one point rather than another because that is the only vulnerable point. The insect cannot choose what wound it will inflict; it stings where it must. Its wonderful operative method is the necessary result of the victim's structure. Let us first, if we attach any importance to lucidity, come to an understanding about the word "vulnerable." Do you mean by this that the point or rather points wounded by the sting are the only points at which a lesion will suddenly cause either death or paralysis? If so, I share your opinion; not only do I share it, but I was the first to proclaim it. My whole thesis is contained in that. Yes, a hundred times yes, the points wounded are the only vulnerable points; they are even very vulnerable; they are the only points which lend themselves to the infliction of sudden death or else paralysis, according to the operator's intention.

But this is not how you understand the matter: you mean accessible to the sting, in a word, penetrable. Here we part company. I have against me, I admit, the Weevils and the Buprestes of the Cerceres. These mailed ones hardly give the sting a chance, save behind the prothorax, the point at which the lancet is actually directed. If I were one to stand on trifles, I might observe that in front of the prothorax, under the throat, is an accessible spot and that the Cerceres will have nothing to do with it. But let us proceed; I give up the horn-clad Beetle.

What are we to say of the Grey Worm and other caterpillars beloved of the Ammophilae? Here are victims accessible to the sting underneath, on the back, on the sides, fore and aft, everywhere with the same facility, excepting the top of the head. And of this infinity of points, which are equally penetrable, the Wasp selects ten, always the same, differing in no way from the rest, unless it be by the close proximity of the nerve-centres. What are we to say of the Cetonia- and Anoxia-larvae, which are always attacked in the first thoracic segment, after long and painful struggles, when the a.s.sailant can sting the grub freely at whatever point she chooses, since it is quite naked and offers no greater resistance to the lancet at one point than at another?

What are we to think of the Sphex' Crickets and Ephippigers, stabbed three times on the side of the thorax, which is fairly well defended, whereas the abdomen, soft and bulky, into which the sting would sink like a needle into a pat of b.u.t.ter, is neglected? Do not let us forget the Philanthus, who takes no account either of the fissures beneath the abdominal plates or of the wide hiatus behind the corselet, but plunges her weapon, at the base of the throat, through a gap of a fraction of a millimetre. Let us just mention the Mantis-hunting Tachytes. Does she make for the most undefended point when she stabs, first of all, at its base, the Mantis' dreadful engine--the arm-pieces each fitted with a double saw--at the risk of being seized, transfixed and crunched on the spot if she misses her blow? Why does she not strike at the creature's long abdomen? That would be quite easy and free from danger.

And the Calicurgi, if you please. Are they also unskilled duelists, plunging the dirk into the only easily accessible point, when their very first move is to paralyse the poison-fangs? If there is one point about the Tarantula and the Epeira that is dangerous and difficult to attack, it is certainly the mouth which bites with its two poisoned harpoons.

And these desperadoes dare to brave that deadly trap! Why do they not follow your judicious advice? They should sting the plump belly, which is wholly unprotected. They do not; and they have their reasons, as have the others.

All, from the first to the last, show us, clear as water from the rock, that the outer structure of the victims operated on counts for nothing in the method of operating. This is determined by the inner anatomy. The points wounded are not stung because they are the only points penetrable by the lancet; they are stung because they fulfil an important condition, without which penetrability loses its value. This condition is none other than the immediate proximity of the nerve-centres whose influence has to be suppressed. When at close quarters with her prey, whether soft or armour-clad, the huntress behaves as if she understood the nervous system better than any of us. The thoughtless objection about the only penetrable points is, I hope, swept aside forever.

I am also told:

"It is possible, if it comes to that, for the sting to be delivered in the neighbourhood of the nerve-centres; in a victim at most three or four centimetres long, distances are very small. But a casual there or thereabouts is a very different thing from the precision of which you speak."

Oh, they are "thereabouts," are they? We shall see! You want figures, millimetres, fractions? You shall have them!

First I call to witness the Interrupted Scolia. If the reader no longer has her method of operating in mind, I will beg him to refresh his memory. The two adversaries, in the preliminary conflict, may be fairly well represented by two rings interlocked not in the same plane but at right angles. The Scolia grips a point of the Anoxia-grub's thorax; she curves her body underneath it and, while encircling the grub, gropes with the tip of her abdomen along the median line of the larva's neck.

Owing to her transversal position, the a.s.sailant is now free to aim her weapon in a slightly slanting direction, whether towards the head or towards the thorax, at the same point of entry in the larva's throat.

Between the two opposite slants of the sting, which is itself very short, what can the distance be? Two millimetres (.078 inch.--Translator's Note.), perhaps less. That is very little. No matter: let the operator make a mistake of this length--negligible, you may tell me--let the sting slant towards the head instead of slanting towards the thorax; and the result of the operation will be entirely different. With a slant towards the head, the cerebral ganglia are wounded and their lesion causes sudden death. This is the stroke of the Philanthus, who kills her Bee by stinging her from below, under the chin. The Scolia needed a motionless but not dead victim, one that would supply fresh victuals; she will now have only a corpse, which will soon go bad and poison the larva.

With a slant towards the thorax, the sting wounds the little ma.s.s of nerve-cells in the thorax. This is the regulation stroke, the one which will induce paralysis and leave the small amount of life needed to keep the provisions fresh. A millimetre higher kills; a millimetre lower paralyses. On this tiny deviation the salvation of the Scolia race depends. You need not fear that the operator will make any mistake in this micrometrical performance: her sting always slants towards the thorax, although the opposite inclination is just as practicable and easy. What would be the outcome of a there or thereabouts under these conditions? Very often a corpse, a form of food fatal to the grub.

The Two-banded Scolia stings a little lower down, on the line of demarcation between the first two thoracic segments. Her position is likewise transversal in relation to the Cetonia-grub; but the distance of the cervical ganglia from the point where the sting enters would possibly not allow the weapon turned towards the head to inflict a lesion followed by sudden death as in the above instance. I am calling this witness with another object. It is extremely unusual for the operator, no matter what her prey or her method, to make a slight mistake and sting merely somewhere near the requisite point. I see them all groping with the tip of the abdomen, sometimes seeking persistently, before unsheathing. They thrust only when the point beneath the sting is precisely that at which the wound will produce its full effect. The Two-banded Scolia in particular will struggle with the Cetonia-grub for half an hour at a time to enable herself to drive in the stiletto at the right spot.

Wearied by an endless scuffle, one of my captives committed before my eyes a slight blunder, an unprecedented thing. Her weapon entered a little to one side, not quite a millimetre from the central point and still, of course, on the line of demarcation between the first two thoracic segments. I at once laid hold of the precious specimen, which was to teach me curious matters about the effects of an ill-delivered stroke. If I myself had made the insect sting at this or that point, there would have been no particular interest in it: the Scolia, held between the finger-tips, would wound at random, like a Bee defending herself; her undirected sting would inject the poison at haphazard.

But here everything happened by rule, except for the little error of position.

Well, the victim of this clumsy operation has its legs paralysed only on the left side, the side towards which the weapon was deflected; it is a case of hemiplegia. The legs on the right side move. If the operation had been performed in the normal fashion the result would have been sudden inertia of all six legs. The hemiplegia, it is true does not last long. The torpor of the left half rapidly gains the right half of the body and the creature lies motionless, incapable of burying itself in the mould, without, however, realizing the conditions indispensable to the safety of the egg or the young grub. If I seize one of its legs or a point of the skin with the tweezers, it suddenly shrivels and curls up and swells out again, as it does when in complete possession of its energies. What would become of an egg laid on such victuals? At the first closing of this ruthless vice, at the first contraction, it would be crushed, or at least detached from its place; and any egg removed from the point where the mother has fastened it is bound to perish. It needs, on the Cetonia's abdomen, a yielding support which the bites of the new-born larva will not set aquiver. The slightly eccentric sting gives none of this soft ma.s.s of fat, always outstretched and quiescent.

Only on the following day, after the torpor has made progress, does the larva become suitably inert and limp. But it is too late; and in the meantime the egg would be in serious danger on this half-paralysed victim. The sting, by straying less than a millimetre, would leave the Scolia without progeny.

I promised fractions. Here they are. Let us consider the Tarantula and the Epeira on whom the Calicurgi have just operated. The first thrust of the sting is delivered in the mouth. In both victims the poison-fangs are absolutely lifeless: tickling with a bit of straw never once succeeds in making them open. On the other hand, the palpi, their very near neighbours, their adjuncts as it were, possess their customary mobility. Without any previous touches, they keep on moving for weeks.

In entering the mouth the sting did not reach the cervical ganglia, or sudden death would have ensued and we should have before our eyes corpses which would go bad in a few days, instead of fresh carcases in which traces of life remain manifest for a long time. The cephalic nerve-centres have been spared.

What is wounded then, to procure this profound inertia of the poison-fangs? I regret that my anatomical knowledge leaves me undecided on this point. Are the fangs actuated by a special ganglion? Are they actuated by fibres issuing from centres exercising further functions? I leave to anatomists equipped with more delicate instruments than I the task of elucidating this obscure question. The second conjecture appears to me the more probable, because of the palpi, whose nerves, it seems to me, must have the same origin as those of the fangs. Basing our argument on this latter hypothesis, we see that the Calicurgus has only one means of suppressing the movement of the poisoned pincers without affecting the mobility of the palpi, above all without injuring the cephalic centres and thus producing death, namely, to reach with her sting the two fibres actuating the fangs, fibres as fine as a hair.

I insist upon this point. Despite their extreme delicacy, these two filaments must be injured directly; for, if it were enough for the sting to inject its poison "there or thereabouts," the nerves of the palpi, so close to the first, would undergo the same intoxication as the adjacent region and would leave those appendages motionless. The palpi move; they retain their mobility for a considerable period; the action of the poison, therefore, is evidently situated in the nerves of the fangs.

There are two of these nerve-filaments, very fine, very difficult to discover, even by the professional anatomist. The Calicurgus has to reach them one after the other, to moisten them with her poison, possibly to transfix them, in any case to operate upon them in a very restricted manner; so that the diffusion of the virus may not involve the adjoining parts. The extreme delicacy of this surgery explains why the weapon remains in the mouth so long; the point of the sting is seeking and eventually finds the tiny fraction of a millimetre where the poison is to act. This is what we learn from the movements of the palpi close to the motionless fangs; they tell us that the Calicurgi are vivisectors of alarming accuracy.

If we accept the hypothesis of a special nerve-centre for the mandibles, the difficulty would be a little less, without detracting from the operator's talent. The sting would then have to reach a barely visible speck, an atom in which we should hardly find room for the point of a needle. This is the difficulty which the various paralysers solve in ordinary practice. Do they actually wound with their dirks the ganglion whose influence is to be done away with? It is possible, but I have tried no test to make sure, the infinitely tiny wound appearing to be too difficult to detect with the optical instruments at my disposal. Do they confine themselves to lodging their drop of poison on the ganglion, or at all events in its immediate neighbourhood? I do not say no.

I declare moreover, that, to provoke lightning paralysis, the poison, if it is not deposited inside the ma.s.s of nervous substance, must act from somewhere very near. This a.s.sertion is merely echoing what the Two-banded Scolia has just shown us: her Cetonia-grub, stung less than a millimetre from the regular spot, did not become motionless until next day. There is no doubt, judging by this instance, that the effect of the virus spreads in all directions within a radius of some extent; but this diffusion is not enough for the operator, who requires for her egg, which is soon to be laid, absolute safety from the very first.

On the other hand, the actions of the paralysers argue a precise search for the ganglia, at all events for the first thoracic ganglion, the most important of all. The Hairy Ammophila, among others, affords us an excellent example of this method. Her three thrusts in the caterpillar's thorax and especially the last, between the first and second pair of legs, are more prolonged than the stabs distributed among the abdominal ganglia. Everything justifies us in believing that, for these decisive inoculations, the sting seeks out the corresponding ganglion and acts only when it finds it under its point. On the abdomen this peculiar insistence ceases; the sting pa.s.ses swiftly from one segment to another.

For these segments, which are less dangerous, the Ammophila perhaps relies on the diffusion of her venom; in any case, the injections, though hastily administered, do not diverge from a close vicinity of the ganglia, for their field of action is very limited, as is proved by the number of inoculations necessary to induce complete torpor, or, more simply, by the following example.