More Hunting Wasps

by Jean-Henri Fabre

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?