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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.

Meanwhile, the larva continues to move along on its back. Suddenly it curls
up; with a stroke of its head it hurls the enemy to a distance.
Undiscouraged by all her set-backs, the Wasp picks herself up, brushes her
wings and resumes her attack upon the colossus, almost always by mounting
the larva's hinder end. At last after all these fruitless attempts, the
Scolia succeeds in achieving the correct position. She is seated athwart
the Cetonia-grub; the mandibles grip a point on the dorsal surface of the
thorax; the body, bent into a bow, passes under the larva and with the tip
of the belly reaches the region of the neck. The Cetonia-grub, placed in
serious peril, writhes, coils and uncoils itself, spinning round upon its
axis. The Scolia does not interfere. Holding the victim tightly gripped,
she turns with it, allows herself to be dragged upwards, downwards,
sidewards, following its contortions. Her obstinacy is such that I can now
remove the bell-glass and follow the details of the drama in the open.

Briefly, in spite of the turmoil, the tip of the abdomen feels that the
right spot has been found. Then and only then the sting is unsheathed. It
plunges in. The thing is done. The larva, at first plump and active,
suddenly becomes flaccid and inert. It is paralysed. Henceforth there are
no movements save of the antennae and the mouthparts, which will for a long
time yet bear witness to a remnant of life. The point wounded has never
varied in the series of combats under glass: it occupies the middle of the
line of demarcation between the prothorax and the mesothorax, on the
ventral surface. Note that the Cerceres, operating on Weevils, whose
nervous system is as compact as the Cetonia-grub's, drive in the needle at
the same spot. Similarity of nervous organization occasions similarity of
method. Note also that the Scolia's sting remains in the wound for some
time and roots about with marked persistence. Judging by the movements of
the tip of the abdomen, one would certainly say that the weapon is
exploring and selecting. Free to shift in one direction or the other,
within narrow limits, its point is most probably seeking for the little
mass of nerve-tissue which must be pricked, or at least sprinkled with
poison, to obtain overwhelming paralysis.

I will not close this report of the duel without relating a few further
facts, of minor importance. The Two-banded Scolia is a fierce persecutor of
the Cetonia. In one sitting the same mother stabs three larvae, one after
the other, in front of my eyes. She refuses the fourth, perhaps owing to
fatigue or to exhaustion of the poison-bag. Her refusal is only temporary.
Next day, she begins again and paralyses two grubs; the day after that, she
does the same, but with a zeal that decreases from day to day.

The other Hunting Wasps that pursue the chase far afield grip, drag, carry
their prey, after depriving it of movement, each in her own fashion and,
laden with their burden, make prolonged attempts to escape from the bell-
glass and to gain the burrow. Discouraged by these futile endeavours, they
abandon them at last. The Scolia does not remove her quarry, which lies on
its back for an indefinite time on the actual spot of the sacrifice. When
she has withdrawn her dagger from the wound, she leaves her victim where it
lies and, without taking further notice of it, begins to flutter against
the side of the glass. The paralysed carcase is not transported elsewhere,
into a special cellar; there where the struggle has occurred it receives,
upon its extended abdomen, the egg whence the consumer of the succulent
tit-bit will emerge, thus saving the expense of setting up house. It goes
without saying that under the bell-glass the laying does not take place:
the mother is too cautious to abandon her egg to the perils of the open
air.

Why then, recognizing the absence of her underground burrow, does the
Scolia uselessly pursue the Cetonia with the frantic ardour of the
Philanthus flinging herself upon the Bee? The action of the Philanthus is
explained by her passion for honey; hence the murders committed in excess
of the needs of her family. The Scolia leaves us perplexed: she takes
nothing from the Cetonia-grub, which is left without an egg; she stabs,
though well aware of the uselessness of her action: the heap of mould is
lacking and it is not her custom to transport her prey. The other
prisoners, once the blow is struck, at least seek to escape with their
capture between their legs; the Scolia attempts nothing.

After due reflection, I lump together in my suspicions all these surgeons
and ask myself whether they possess the slightest foresight, where the egg
is concerned. When, exhausted by their burden, they recognize the
impossibility of escape, the more expert among them ought not to begin all
over again; yet they do so begin a few minutes later. These wonderful
anatomists know absolutely nothing about anything, they do not even know
what their victims are good for. Admirable artists in killing and
paralysis, they kill or paralyse at every favourable opportunity, no matter
what the final result as regards the egg. Their talent, which leaves our
science speechless, has not a shadow of consciousness of the task
accomplished.

A second detail strikes me: the desperate persistence of the Scolia. I have
seen the struggle continue for more than a quarter of an hour, with
frequent alternations of good luck and bad, before the Wasp achieved the
required position and reached with the end of her abdomen the spot where
the sting should penetrate. During these assaults, which were resumed as
soon as they were repulsed, the aggressor repeatedly applied the tip of her
belly to the larva, but without unsheathing, as I could see by the absence
of the start which the larva gives when it feels the pain of the sting. The
Scolia therefore does not prick the Cetonia anywhere until the weapon
covers the requisite spot. If no wounds are inflicted elsewhere, this is
not in any way due to the structure of the larva, which is soft and
vulnerable all over, except in the head. The point sought by the sting is
no more unprotected than any other part of the skin.

In the scuffle, the Scolia, curved into a bow, is sometimes seized by the
vice-like grip of the Cetonia-grub, which is violently coiling and
uncoiling. Heedless of the powerful grip, the Wasp does not let go for a
moment, either with her mandibles or with the tip of her abdomen. At such
times the two creatures, locked in a mutual embrace, turn over and over in
a mad whirl, each of them now on top, now underneath. When it contrives to
rid itself of its enemy, the larva uncoils again, stretches itself out and
proceeds to make off upon its back with all possible speed. Its defensive
ruses are exhausted. Formerly, before I had seen things for myself, taking
probability as my guide I willingly granted to the larva the trick of the
Hedgehog, who rolls himself into a ball and sets the Dog at defiance.
Coiled upon itself, with an energy which my fingers have some difficulty in
overcoming, the larva, I thought, would defy the Scolia, powerless to
unroll it and disdaining any point but the one selected. I hoped and
believed that it possessed this means of defence, a means both efficacious
and extremely simple. I had presumed too much upon its ingenuity. Instead
of imitating the Hedgehog and remaining contracted, it flees, belly in air;
it foolishly adopts the very posture which allows the Scolia to mount to
the assault and to reach the spot for the fatal stroke. The silly beast
reminds me of the giddy Bee who comes and flings herself into the clutches
of the Philanthus. Yet another who has learnt no lesson from the struggle
for life.

Let us proceed to further examples. I have just captured an Interrupted
Scolia (Colpa interrupta, LATR.), exploring the sand, doubtless in search
of game. It is a matter of making the earliest possible use of her, before
her spirit is chilled by the tedium of captivity. I know her prey, the
larva of Anoxia australis (The Anoxia are a genus of Beetles akin to the
Cockchafers.--Translator's Note.); I know, from my past excavations, the
points favoured by the grub: the mounds of sand heaped up by the wind at
the foot of the rosemaries on the neighbouring hill-sides. It will be a
hard job to find it, for nothing is rarer than the common if one wants it
then and there. I appeal for assistance to my father, an old man of ninety,
still straight as a capital I. Under a sun hot enough to broil an egg, we
set off, shouldering a navvy's shovel and a three-pronged luchet. (The
local pitchfork of southern France.--Translator's Note.) Employing our
feeble energies in turns, we dig a trench in the sand where I hope to find
the Anoxia. My hopes are not disappointed. After having by the sweat of our
brow--never was the expression more justified--removed and sifted two cubic
yards at least of sandy soil with our fingers, we find ourselves in
possession of two larvae. If I had not wanted any, I should have turned
them up by the handful. But my poor and costly harvest is sufficient for
the moment. To-morrow I will send more vigorous arms to continue the work
of excavation.

And now let us reward ourselves for our trouble by studying the tragedy in
the bell-glass. Clumsy, awkward in her movements, the Scolia slowly goes
the round of the circus. At the sight of the game, her attention is
aroused. The struggle is announced by the same preparations as those
displayed by the Two-banded Scolia: the Wasp polishes her wings and taps
the table with the tips of her antennae. And view, halloo! The attack
begins. Unable to move on a flat surface, because of its short and feeble
legs, deprived moreover of the Cetonia-larva's eccentric means of
travelling on its back, the portly grub has no thought of fleeing; it coils
itself up. The Scolia, with her powerful pincers, grips its skin now here,
now elsewhere. Curved into a circle with the two ends almost touching, she
strives to thrust the tip of her abdomen into the narrow opening in the
coil formed by the larva. The contest is conducted calmly, without violent
bouts at each varying accident. It is the determined attempt of a living
split ring trying to slip one of its ends into another living split ring,
which with equal determination refuses to open. The Scolia holds the victim
subdued with her legs and mandibles; she tries one side, then the other,
without managing to unroll the circle, which contracts still more as it
feels its danger increasing. The actual circumstances make the operation
more difficult: the prey slips and rolls about the table when the insect
handles it too violently; there are no points of purchase and the sting
cannot reach the desired spot; the fruitless efforts are continued for more
than an hour, interrupted by periods of rest, during which the two
adversaries represent two narrow, interlocked rings.

What ought the powerful Cetonia-grub to do to defy the Two-banded Scolia,
who is far less vigorous than her victim? It should imitate the Anoxia-
larva and remain rolled up like a Hedgehog until the enemy retires. It
tries to escape, unrolls itself and is lost. The other does not stir from
its posture of defence and resists successfully. Is this due to acquired
caution? No, but to the impossibility of doing otherwise on the slippery
surface of a table. Clumsy, obese, weak in the legs, curved into a hook
like the common White Worm (The larva of the Cockchafer.--Translator's
Note.), the Anoxia-larva is unable to move along a smooth surface; it
writhes laboriously, lying on its side. It needs the shifting soil in
which, using its mandibles as a plough-share, it digs into the ground and
buries itself.

Let us try if sand will shorten the struggle, for I see no end to it yet,
after more than an hour of waiting. I lightly powder the arena. The attack
is resumed with a vengeance. The larva, feeling the sand, its native
element, tries to escape. Imprudent creature! Did I not say that its
obstinacy in remaining rolled up was due to no acquired prudence but to the
necessity of the moment? The sad experience of past adversities has not yet
taught it the precious advantage which it might derive from keeping its
coils closed so long as danger remains. For that matter, on the unyielding
support of my table, they are not one and all so cautious. The larger seem
even to have forgotten what they knew so well in their youth: the defensive
art of coiling themselves up.

I continue my story with a fine-sized specimen, less likely to slip under
the Scolia's onslaught. When attacked, the larva does not curl up, does not
shrink into a ring as did the last, which was younger and only half as
large. It struggles awkwardly, lying on its side, half-open. For all
defence it twists about; it opens, closes and reopens the great hooks of
its mandibles. The Scolia grabs it at random, clasps it in her shaggy legs
and for nearly a quarter of an hour battles with the luscious tit-bit. At
last, after a not very tumultuous struggle, when the favourable position is
attained and the propitious moment has come, the sting is implanted in the
creature's thorax, in a central point, below the throat, level with the
fore-legs. The effect is instantaneous: total inertia, except of the
appendages of the head, the antennae and mouth-parts. I achieved the same
results, the same prick at a definite, invariable point, with my several
operators, renewed from time to time by some lucky cast of the net.

Let us mention, in conclusion, that the attack of the Interrupted Scolia is
far less fierce than that of the Two-banded Scolia. The Wasp, a rough sand-
digger, has a clumsy gait; her movements are stiff and almost automatic.
She does not find it easy to repeat her dagger-thrust. Most of the
specimens with which I experimented refused a second victim on the first
two days after their exploits. As though somnolent, they did not stir
unless excited by my teasing them with a bit of straw. Although more active
and more ardent in the chase, the Two-banded Scolia likewise does not draw
her weapon every time that I invite her. For all these huntresses there are
moments of inaction which the presence of a fresh prey is powerless to
disturb.

The Scoliae have taught me nothing further, in the absence of subjects
belonging to other species. No matter: the results obtained represent no
small triumph for my ideas. Before seeing the Scoliae operate, I said,
guided solely by the anatomy of the victims, that the Cetonia-, Anoxia- and
Oryctes-larvae must be paralysed by a single thrust of the lancet; I even
named the point where the sting must strike, a central point, in the
immediate vicinity of the fore-legs. Of the three genera of paralysers, two
have allowed me to witness their surgical methods, which the third, I feel
certain, will confirm. In both cases, a single thrust of the lancet; in
both cases, injection of the venom at a predetermined point. A calculator
in an observatory could not compute the position of his planet with greater
accuracy. An idea may be taken as proved when it attains to this
mathematical forecast of the future, this certain knowledge of the unknown.
When will the acclaimers of chance achieve a like success? Order appeals to
order; and chance knows no laws.





Next: THE METHOD OF THE CALICURGI

Previous: THE METHOD OF THE AMMOPHILAE.



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