Chapter XIV. Objections and Rejoinders
Jean-Henri Fabre More Hunting Wasp
Saddle-backed Bush Cricket (Ephippiger ephippiger)
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 pass 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 assailant 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 butter, 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 assailant 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 (1), 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 mass 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 mass 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 mass of nervous substance, must act from somewhere very near. This assertion 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 passes 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.
A Grey Worm which had just received its first sting on the third thoracic segment repulses the Ammophila and with a jerk hurls her to a distance. I profit by the occasion and take hold of the grub. The legs of this third segment only are paralysed; the others retain their usual mobility. However helpless in the two injured legs, the animal can walk very well; it buries itself in the earth, returning to the surface at night to gnaw the stump of lettuce with which I have served it. For a fortnight my paralytic retains perfect liberty of action, except in the segment operated on; then it dies, not of its wound but accidentally. All this time the effect of the poison has not spread beyond the inoculated segment.
At any point where the sting enters, anatomy informs us of the presence of a nervous nucleus. Is this centre directly smitten by the weapon? Or is it poisoned with virus, from a very small distance, by the progressive impregnation of the neighbouring tissues? This is the doubtful point, though it does not in any way invalidate the precision of the abdominal injections, which are comparatively neglected. As for those in the caterpillar's thorax, their precision is beyond dispute. After the Ammophilae, the Scoliae and, above all, the Calicurgi, is it really necessary to bring into court yet other witnesses, who would all swear that, with modifications of detail, the movement of their lancet is strictly regulated by the nervous system of the prey? This ought to be enough. The proof is established for those who have ears to hear with.
Others delight in objections whose oddity surprises me. They see in the poison of the Hunting Wasps an antiseptic liquid and in victuals stored in their burrows preserved meats which are kept fresh not by a remnant of life but by the virus and its microbes. Come, my learned masters, let us just talk the matter over, between ourselves. Have you ever seen the larder of a skilled Hunting Wasp, a Sphex for instance, a Scolia, an Ammophila? You haven't, have you? I thought as much. Yet it would be better to begin by doing so, before bringing the preservative microbe on the scene. The slightest examination would have shown you that the victuals cannot be compared exactly with smoked hams. The thing moves, therefore it is not dead. There you have the whole matter, in its artless simplicity. The palpi move, the mandibles open and shut, the tarsi quiver, the antennae and the abdominal filaments wave to and fro, the abdomen throbs, the intestine rejects its contents, the animal reacts to the stimulus of a needle, all of which signs are hardly compatible with the idea of pickled meat.
Have you had the curiosity to look through the pages in which I set forth the detailed results of my observations? You haven't, have you? Again, I thought as much. It is a pity. You would there find, in particular, the history of certain Ephippigers who, after being stung by the Sphex according to rule, were reared by myself by hand. You must agree that these are queer preserves to be produced by the use of an antiseptic fluid. They accept the mouthfuls which I offer them on the tip of a straw; they feed, they sit up and take nourishment. I shall never live to see tinned sardines doing as much.
I will avoid tedious repetition and content myself with adding to my old sheaf of proofs a few facts which have not yet been related. The Nest-building Odynerus showed us in her cells a few Chrysomela-larvae fixed by the hinder part to the side of the reed. The grub fastens itself in this way to the poplar-leaf to obtain a purchase when the moment has come for leaving the larval slough. Do not these preparations for the nymphosis tell us plainly that the creature is not dead?
The Hairy Ammophila affords us an even better example. A number of caterpillars operated on before my eyes attained, some sooner, some later, the chrysalis stage. My notes are explicit on the subject of some of them, taken on Verbascum sinuatum. Sacrificed on the 14th of April, they were still irritable when tickled with a straw a fortnight after. A little later, the pale-green colouring of the early stages is replaced by a reddish brown, except on two or three segments of the median ventral surface. The skin wrinkles and splits, but does not come detached of its own accord. I can easily remove it in shreds. Under this slough appears the firm, chestnut-brown horn integument of the chrysalis. The development of the nymphosis is so correct that for a moment the crazy hope occurs to me that I may see a Turnip-moth come out of this mummy, the victim of a dozen dagger-thrusts. For the rest, there is no attempt at spinning a cocoon, no jet of silky threads flung out by the caterpillar before turning into a chrysalis. Perhaps under normal conditions metamorphosis takes place without this protection. However, the moth whom I expected to see was beyond the limits of the possible. In the middle of May, a month after the operation on the caterpillars, my three chrysalids, still incomplete underneath, in the three or four middle segments, withered and at last went mouldy. Is the evidence conclusive this time? Who can conceive such a silly idea as that a prey really dead, a corpse preserved from putrefaction by an antiseptic, could contain what is perhaps the most delicate work of life, the development of the grub into the perfect insect?
The truth must be driven into recalcitrant brains with great blows of the sledge-hammer. Let us once more employ this method. In September I unearth from a heap of mould five Cetonia-grubs, paralysed by the Two-banded Scolia and bearing on the abdomen the as yet unhatched egg of the Wasp. I remove the eggs and install the helpless creatures on a bed of leaf-mould with a glass cover. I propose to see how long I can keep them fresh, able to move their mandibles and palpi. Already the victims of various Hunting Wasps had instructed me on a similar matter; I knew that traces of life linger for two, three, four weeks and longer. For instance, I had seen the Ephippigers of the Languedocian Sphex continue the waving of their antennae and their paralytic shudders for forty days of artificial feeding by hand; and I used to wonder whether the more or less early death of the other victims was not due to lack of nourishment quite as much as to the operation which they had undergone. However, the insect in its adult form usually has a very brief existence. It soon dies, killed by the mere fact of living, without any other accident. A larva is preferable for these investigations. Its constitution is livelier, better able to support protracted abstinence, above all during the winter torpor. The Cetonia-grub, a regular lump of bacon, nourished by its own fat during the winter season, fulfils the needful conditions to perfection. What will become of it, lying belly upwards on its bed of leaf-mould? Will it survive the winter?
At the end of a month, three of my grubs turn brown and lapse into rottenness. The other two keep perfectly fresh and move their antennae and palpi at the touch of a straw. The cold weather comes and tickling no longer elicits these signs of life. The inertia is complete; nevertheless their appearance remains excellent, without a trace of the brownish tinge, the sign of deterioration. At the return of the warm weather, in the middle of May, there is a sort of resurrection. I find my two larvae turned over, belly downwards; much more: they are half-buried in the mould. When teased, they coil up lazily; they move their legs as well as their mouth-parts, but slowly and without vigour. Then their strength seems to revive. The convalescent, resuscitated grubs dig with clumsy efforts into their bed of mould; they dive into it and disappear to a depth of about two inches. Recovery seems to be imminent.
I am mistaken. In June I unearth the invalids. This time, the larvae are dead; their brown colour tells me as much. I expected better things. Never mind: this is no trifling success. For nine months, nine long months, the grubs stabbed by the Scolia kept fresh and alive. Towards the end, torpor was dispelled, strength and movement returned, sufficiently to enable them to leave the surface where I had placed them and to regain the depths by boring a passage through the soil. I really think that after this resurrection there will be no more talk of antiseptics, unless and until tinned Herrings begin to frolic in their brine (2).
1. .078 inch.
2. The subject of this and the preceding chapters is continued in an essay entitled „The Poison of the Bee“ for which cf. „Bramble-bees and Others“: chapter 11.