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 (.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 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.
