More Hunting Wasps

by Jean-Henri Fabre

A similar muscular energy is found in the larvae of the Oryctes (Also known as the Rhinoceros Beetle.—Translator's Note.), the Anoxia (A Beetle akin to the Cockchafer.—Translator's Note.), the Cockchafer. Weighed down by a heavy belly and living underground, where they feed either on leaf-mould or on roots, these larvae all possess the vigorous constitution needed to drag their corpulence through a resisting medium. All of them also roll themselves into a hook which is not straightened without an effort.

Now what would become of the egg and the new-born grub of the Scoliae, fixed under the belly, at the centre of the Cetonia's spiral, or inside the hook of the Oryctes or the Anoxia? They would be crushed between the jaws of the living vice. It is essential that the arc should slacken and the hook unbend, without the least possibility of their returning to a state of tension. Indeed, the well-being of the Scoliae demands something more: those powerful bodies must not retain even the power to quiver, lest they derange a method of feeding which has to be conducted with the greatest caution.

The Cetonia-grub to which the Two-banded Scolia's egg is fastened fulfils the required conditions admirably. It is lying on its back, in the midst of the mould, with its belly fully extended. Long accustomed though I be to this spectacle of victims paralysed by the sting of the Hunting Wasp, I cannot suppress my astonishment at the profound immobility of the prey before my eyes. In the other victims with flexible skins, Caterpillars, Crickets, Mantes, Ephippigers, I perceived at least some pulsations of the abdomen, a few feeble contortions under the stimulus of a needle. There is nothing of the sort here, nothing but absolute inertia, except in the head, where I see, from time to time, the mouth-parts open and close, the palpi give a tremor, the short antennae sway to and fro. A prick with the point of a needle causes no contraction, no matter what the spot pricked. Though I stab it through and through, the creature does not stir, be it ever so little. A corpse is not more inert. Never, since my remotest investigations, have I witnessed so profound a paralysis. I have seen many wonders due to the surgical talent of the Wasp; but to-day's marvel surpasses them all.

I am doubly surprised when I consider the unfavourable conditions under which the Scolia operates. The other paralysers work in the open air, in the full light of day. There is nothing to hinder them. They enjoy full liberty of action in seizing the prey, holding it in position and sacrificing it; they are able to see the victim and to parry its means of defence, to avoid its spears, its pincers. The spot or spots to be attained are within their reach; they drive the dagger in without let or hindrance.

What difficulties, on the other hand, await the Scolia! She hunts underground, in the blackest darkness. Her movements are laboured and uncertain, owing to the mould, which is continually giving way all round her; she cannot keep her eyes on the terrible mandibles, which are capable of cutting her body in two with a single bite. Moreover, the Cetonia-grub, perceiving that the enemy is approaching, assumes its defensive posture, rolls itself up and makes a shield for its only vulnerable part, the ventral surface, with its convex back. No, it cannot be an easy operation to subdue the powerful larva in its underground retreat and to stab with the precision which immediate paralysis requires.

We wish that we might witness the struggle between the two adversaries and see at first hand what happens, but we cannot hope to succeed. It all takes place in the mysterious darkness of the soil; in broad daylight, the attack would not be delivered, for the victim must remain where it is and then and there receive the egg, which is unable to thrive and develop except under the warm cover of vegetable mould. If direct observation is impracticable, we can at least foresee the main outlines of the drama by allowing ourselves to be guided by the warlike manoeuvres of other burrowers.

I picture things thus: digging and rummaging through the heap of mould, guided perhaps by that singular sensibility of the antennae which enables the Hairy Ammophila to discover the Grey Worm (The caterpillar of the Turnip Moth. Cf. "The Hunting Wasps": chapters 18 to 20.—Translator's Note.) underground, the Scolia ends by finding a Cetonia-larva, a good plump one, in the pink of condition, having reached its full growth, just what the grub which is to feed on it requires. Forthwith, the assaulted victim, contracting desperately, rolls itself into a ball. The other seizes it by the skin of the neck. To unroll it is impossible to the insect, for I myself have some trouble in doing so. One single point is accessible to the sting: the under part of the head, or rather of the first segments, which are placed outside the coil, so that the grub's hard cranium makes a rampart for the hinder extremity, which is less well defended. Here the Wasp's sting enters and here only can it enter, within a narrowly circumscribed area. One stab only of the lancet is given at this point, one only because there is no room for more; and this is enough: the larva is absolutely paralysed.

The nervous functions are abolished instantly; the muscular contractions cease; and the animal uncoils like a broken spring. Henceforth motionless, it lies on its back, its ventral surface fully exposed from end to end. On the median line of this surface, towards the rear, near the brown patch due to the alimentary broth contained in the intestine, the Scolia lays her egg and without more ado, leaves everything lying on the actual spot where the murder was committed, in order to go in search of another victim.

This is how the deed must be done: the results prove it emphatically. But then the Cetonia-grub must possess a very exceptional structure in its nervous organization. The larva's violent contraction leaves but a single point of attack open to the sting, the under part of the neck, which is doubtless uncovered when the victim tries to defend itself with its mandibles; and yet a stab in this one point produces the most thorough paralysis that I have ever seen. It is the general rule that larvae possess a centre of innervation for each segment. This is so in particular with the Grey Worm, the sacrificial victim of the Hairy Ammophila. The Wasp is acquainted with this anatomical secret: she stabs the caterpillar again and again, from end to end, segment by segment, ganglion by ganglion. With such an organization the Cetonia-grub, unconquerably coiled upon itself would defy the paralyser's surgical skill.

If the first ganglion were wounded, the others would remain uninjured; and the powerful body, actuated by these last, would lose none of its powers of contraction. Woe then to the egg, to the young grub held fast in its embrace! And how insurmountable would be the difficulties if the Scolia, working in the profound darkness amid the crumbling soil and confronted by a terrible pair of mandibles, had to stab each segment in turn with her sting, with the certainty of method displayed by the Ammophila! The delicate operation is possible in the open air, where nothing stands in the way, in broad daylight, where the sight guides the scalpel, and with a patient which can always be released if it becomes dangerous. But in the dark, underground, amidst the ruins of a ceiling which crumbles in consequence of the conflict and at close quarters with an opponent greatly her superior in strength, how is the Scolia to guide her sting with the accuracy that is essential if the stabs are to be repeated?