I present Jules' Ammophila with a slender, brownish Looper which I caught on the jasmine. The attack is not slow in coming. The caterpillar is grabbed by the neck: lively contortions of the victim, which rolls the aggressor over and drags her along, now uppermost, now undermost in the struggle. First the thorax is stung, in its three rings, from back to front. The sting lingers longest near the throat, in the first segment. This done, the Ammophila releases her victim and proceeds to stamp her tarsi, to polish her wings, to stretch herself. Again I observe the acrobatic postures, the forehead touching the ground, the hinder part of the body raised. This mimic triumph is the same as that of the huntress of the Grey Worm. Then the Looper is once more seized. Despite its contortions, which are not in the least abated by the three wounds in the thorax, it is stung from front to back in each segment still unwounded, no matter how many, whether supplied with legs or not. I expected to see the sting refrain more or less in the long interval which separates the true legs in front from the pro-legs at the back (Fleshy legs found on the abdominal segments of caterpillars and certain other larvae.—Translator's Note.): segments devoid of organs of defence or locomotion did not seem to me to deserve conscientious surgery. I was mistaken: not a segment of the Looper is spared, not even the last ones. It is true that these, being eminently capable of catching hold with their false legs, would be dangerous later were the Wasp to neglect them.
I observe, however, that the lancet works more rapidly in the second part of the operation than in the first, either because the caterpillar, half subjugated by the triple wound at the outset, is easier to reach with the sting, or because the segments more remote from the head are rendered harmless with a smaller injection of poison. Nowhere do we see repeated the care expended upon paralysing the thorax, still less the insistent attention to the first segment. On returning to her Looper after the entr'acte devoted to the joys of success, the Ammophila stabs so swiftly that, on one occasion, I saw her obliged to begin all over again. Lightly stung along its whole length, the victim still struggles. Without hesitation, the operator unsheathes her scalpel for the second time and operates on the Looper afresh, with the exception of the thorax, which was already sufficiently anaesthetized. This done, all is in order; there is no more movement.
After the stiletto the hooks of the mandibles rarely fail to intervene. Long and curved, they nibble at the paralysed victim's neck, sometimes from above, sometimes from below. It is a repetition of what the Hairy Ammophila showed us: the same sudden squeezes of the pincers, with rather long intervals between. These intervals, these measured bites and the insect's watchful attitude have every appearance of telling us that the operator is noting the effect produced before giving a fresh pinch of the nippers.
It will be seen how valuable is the evidence of Jules' Ammophila: it tells us that the immolaters of Looper caterpillars and those of ordinary caterpillars follow precisely the same method; that victims displaying very dissimilar external structure do not entail any modification of the operative tactics so long as the internal organization remains the same. The number, arrangement and degree of mutual independence of the nerve-centres guide the sting; the anatomy of the game, rather than its form, controls the huntress' tactics.
Let me mention, before I dismiss the subject, a superb example of this marvellous anatomical discrimination. I once took from between the legs of a Hairy Ammophila, which had just paralysed it, a caterpillar of Dicranura vinula. What a strange capture compared with the ordinary caterpillar! Bridling in thick folds beneath its pink neckerchief, its fore-part raised in a sphinx-like attitude, its hinder-part slowly waving two long caudal threads, the curious animal is no caterpillar to the schoolboy who brings it to me, nor to the man who comes upon it while cutting his bundle of osiers; but it is a caterpillar to the Ammophila, who treats it accordingly. I explore the queer creature's segments with the point of a needle. All are insensitive; all therefore have been stung.
CHAPTER 12. THE METHOD OF THE SCOLIAE.
After the Ammophilae, the paralysers who multiply their lancet-thrusts to destroy the influence of the various nerve-centres, excepting those of the head, it seemed advisable to interrogate other insects which also are accustomed to a naked prey, vulnerable at all points save the head, but which deliver only a single thrust of the sting. Of these two conditions the Scoliae fulfilled one, with their regular quarry, the tender Cetonia-, Oryctes-or Anoxia-larva, according to the Scolia's species. Did they fulfil the second? I was convinced beforehand that they did. From the anatomy of the victims, with their concentrated nervous system, I foresaw, when compiling my history of the Scoliae, that the sting would be unsheathed once only; I even mentioned the exact spot into which the weapon would be plunged.
These were assertions dictated by the anatomist's scalpel, without the slightest direct proof derived from observed facts. Manoeuvres executed underground escaped the eye, as it seemed to me that they must always do. How indeed could I hope that a creature whose art is practised in the darkness of a heap of mould would decide to work in broad daylight? I did not reckon upon it all. Nevertheless, to salve my conscience, I tried bringing the Scolia into contact with her prey under the bell-glass. I was well-advised to do so, for my success was in inverse ratio to my hopes. Next to the Philanthus, none of the Hunting Wasps displayed such ardour in attacking under artificial conditions. All the insects experimented upon, some sooner, some later, rewarded me for my patience. Let us watch the Two-banded Scolia (S. bifasciata, VAN DER LIND) operating on her Cetonia grub.
The incarcerated larva strives to escape its terrible neighbour. Lying on its back, it fiercely wends its way round and round the glass circus. Presently the Scolia's attention awakens and is betrayed by a continued tapping with the tips of the antennae upon the table, which now represents the accustomed soil. The Wasp attacks the game, delivering her assault upon the monster's hinder end. She climbs upon the Cetonia-grub, obtaining a purchase with the tip of her abdomen. The quarry merely travels the more quickly on its back, without coiling itself into a defensive posture. The Scolia reaches the fore-part, with tumbles and other accidents which vary greatly with the amount of tolerance displayed by the larva, her improvised steed. With her mandibles she nips a point of the thorax, on the upper surface; she places herself athwart the beast, arches herself and makes every effort to reach with the end of her abdomen the region into which the sting is to be driven. The arch is a little too narrow to embrace almost the whole circumference of her corpulent prey; and she renews her attempts and efforts for a long time. The tip of the belly tries every conceivable expedient, touching here, there and everywhere, but as yet stopping nowhere. This persistent search in itself demonstrates the importance which the paralyser attaches to the point at which her lancet is to penetrate the flesh.