More Hunting Wasps

by Jean-Henri Fabre

SECOND ACT.—When the operation is resumed, the caterpillar is seized by the back. From front to rear, in order, all the segments are stung on the ventral surface, except the three operated on. All serious danger is averted by the stabs of the first act; therefore, the Wasp is now able to work upon her patient without the haste displayed at the outset. Deliberately and methodically she drives in her lancet, withdraws it, selects the spot, stabs it and begins again, passing from segment to segment, taking care, each time, to lay hold of the back a little more to the rear, in order to bring the segment to be paralysed within reach of the needle. For the second time, the caterpillar is released. It is absolutely inert, except the mandibles, which are still capable of biting.

THIRD ACT.—The Ammophila clasps the paralysed victim between her legs; with the hooks of her mandibles she seizes the back of its neck, at the base of the first thoracic segment. For nearly ten minutes she munches this weak spot, which lies close to the cerebral nerve-centres. The pincers squeeze suddenly but at intervals and methodically, as though the manipulator wished each time to judge of the effect produced; the squeezes are repeated until I am tired of trying to count them. When they cease, the caterpillar's mandibles are motionless. Then comes the transportation of the carcase, a detail which is not relevant in this place.

I have set forth the complete tragedy, as it is fairly often enacted, but not always. The insect is not a machine, unvarying in the effect of its mechanism; it is allowed a certain latitude, enabling it to cope with the eventualities of the moment. Any one expecting to see the incidents of the struggle unfolding themselves exactly as I have described will risk disappointment. Special instances occur—they are even numerous—which are more or less at variance with the general rule. It will be well to mention the more important, in order to put future observers on their guard.

Not infrequently the first act, that of paralysing the thorax, is restricted to two thrusts of the sting instead of three, or even to one, which is then delivered in the foremost segment. This, it would seem, from the persistency with which the Ammophila inflicts it, is the most important prick of all. Is it unreasonable to suppose that the operator, when she begins by pricking the thorax, intends to subdue her capture and to make it incapable of injuring her, or even of disturbing her when the moment comes for the delicate and protracted surgery of the second act? This idea seems to me highly admissible; and then, instead of three dagger-thrusts, why not two only, why not merely one, if this would suffice for the time being? The amount of vigour displayed by the caterpillar must be taken into consideration. Be this as it may, the segments spared in the first act are stabbed in the second. I have sometimes even seen the three thoracic segments stung twice over: at the beginning of the attack and again when the Wasp returned to her vanquished prey.

The Ammophila's triumphant transports beside her wounded and writhing victim are also subject to exceptions. Sometimes, without releasing its prey for a moment, the insect proceeds from the thorax to the next segments and completes its operation in a single spell. The joyous entr'acte does not take place; the convulsive movements of the wings and the acrobatic postures are suppressed.

The rule is paralysis of all the segments, however many, in regular order from front to back, including even the anal segment if this boast of legs. By a fairly frequent exception the last two or three segments are spared. Another exception, but a very rare one, of which I have observed only a single instance, consists in the inversion of the dagger-thrusts of the second act, the thrusts being delivered from back to front. The caterpillar is then seized by its hinder extremity; and the Ammophila, progressing towards the head, stings in reverse order, passing from the succeeding to the preceding segment, including the thorax already stabbed. This reversal of the usual tactics I am inclined to attribute to negligence on the insect's part. Negligence or not, the inverted method has the same final result as the direct method: the paralysis of all the segments.

Lastly, the compression of the neck by the mandibulary pincers, the munching of the weak spot between the base of the skull and the first segment of the thorax, is sometimes practised and sometimes neglected. If the caterpillar's jaws open and threaten, the Ammophila stills them by biting the neck; if they are already growing quiescent, she refrains. Without being indispensable, this operation is useful at the moment of carting the prey. The caterpillar, too heavy to be carried on the wing, is dragged, head first, between the Ammophila's legs. If the mandibles are working, the least clumsiness may render them dangerous to the carrier, who is exposed to their bite without any means of defence.

Moreover, once on the way, thickets of grass are traversed in which the Grey Worm can seize a blade and offer a desperate resistance to the traction. Nor is this all. The Ammophila does not as a rule trouble about her burrow, or at least does not complete it, until she has caught her caterpillar. During the mining-operations, the game is laid somewhere high up, out of reach of the Ants, on some tuft of grass, or the twigs of a shrub, whither the huntress, from time to time, stopping her well-sinking, hastens to see if her quarry is still there. For her this is a means of refreshing her memory of the spot where she has laid it, often at some distance from the burrow, and of preventing attempts at robbery. When the moment comes for removing the game from its hiding-place, the difficulty would be insurmountable were the worm, gripping the shrub with all the might of its jaws, to anchor itself there. Hence inertia of the powerful hooks, which are the paralysed creature's sole means of resistance, becomes essential during the carting. The Ammophila obtains it by compressing the cerebral ganglia, by munching the neck. The inertia is temporary; it wears off sooner or later; but by this time the carcase is in the cell and the egg, prudently laid at a distance on the ventral surface of the worm, has nothing to fear from the caterpillar's grapnels. No comparison is permissible between the methodical squeezes of the Ammophila benumbing the cephalic nerve-centres and the brutal manipulations of the Philanthus emptying the crop of her Bee. The huntress of Grey Worms induces a temporary torpor of the mandibles; the ravisher of Bees makes them eject their honey. No one gifted with the least perspicacity will confound the two operations.

For the moment we will not dwell any longer on the method of the Hairy Ammophila; we will see instead how her kinswomen behave. After protracted refusals the Sandy Ammophila (A. sabulosa, FAB.),on whom I experimented in September, ended by accepting the proffered prey, a powerful caterpillar as thick as a lead-pencil. The surgical method did not differ from that employed by the Hairy Ammophila when operating on her Grey Worm in one spell. All the segments, excepting the last three, were stung from front to back, beginning with the prothorax. This single success with a simplified method left me in ignorance of the accessory manoeuvres, which I do not doubt must more or less closely recall those of the preceding species.

I am all the more inclined to accept these secondary manoeuvres, not as yet recorded—the transports of triumph and the compressions of the neck—inasmuch as I see them practised upon the Looper caterpillars, which differ so greatly from the others in external structure, exactly as I have described them in the case of the Grey Worm, which is of the ordinary form. Two species, the Silky Ammophila (A. holoserica, FAB.) and Jules' Ammophila (See in the first volume of the "Souvenirs entomologiques" what I mean by this denomination.—Author's Note.), affect this curious prey, which moves with the stride of a pair of compasses. The first, often renewed under glass during the greater part of August, has always refused my offers; the second, her contemporary, has, on the contrary, promptly accepted them.