There can be no doubt that the Sphex uses her greatest skill when
immolating a cricket; it is therefore very important to explain the
method by which the victim is sacrificed. Taught by my numerous
attempts to observe the war tactics of the Cerceris, I immediately used
on the Sphex the plan already successful with the former, i.e. taking
away the prey and replacing it by a living specimen. This exchange is
all the easier because, as we have seen, the Sphex leaves her victim
while she goes down her burrow, and the audacious tameness, which
actually allows her to take from your fingertips, or even off your
hand, the cricket stolen from her and now offered, conduces most
happily to a successful result of the experiment by allowing the
details of the drama to be closely observed.
It is easy enough to find living crickets; one has only to lift the
first stone, and you find them, crouched and sheltering from the sun.
These are the young ones of the current year, with only rudimentary
wings, and which, not having the industry of the perfect insect, do not
yet know how to dig deep retreats where they would be beyond the
investigations of the Sphex. In a few moments I find as many crickets
as I could wish, and all my preparations are made. I ascend to the top
of my observatory, establish myself on the flat ground in the midst of
the Sphex colony and wait.
A huntress comes, conveys her cricket to the mouth of her hole and goes
down alone. The cricket is speedily replaced by one of mine, but placed
at some distance from the hole. The Sphex returns, looks round, and
hurries to seize her too distant prey. I am all attention. Nothing on
earth would induce me to give up my part in the drama which I am about
to witness. The frightened cricket springs away. The Sphex follows
closely, reaches it, darts upon it. Then there is a struggle in the
dust when sometimes conqueror, sometimes conquered is uppermost or
undermost. Success, equal for a moment, finally crowns the aggressor.
In spite of vigorous kicks, in spite of bites from its pincer-like
jaws, the cricket is felled and stretched on its back.
The murderess soon makes her arrangements. She places herself body to
body with her adversary, but in a reverse position, seizes one of the
bands at the end of the cricket’s abdomen and masters with her forefeet
the convulsive efforts of its great hind-thighs. At the same moment her
intermediate feet squeeze the panting sides of the vanquished cricket,
and her hind ones press like two levers on its face, causing the
articulation of the neck to gape open. The Sphex then curves her
abdomen vertically, so as to offer a convex surface impossible for the
mandibles of the cricket to seize, and one beholds, not without
emotion, the poisoned lancet plunge once into the victim’s neck, next
into the jointing of the two front segments of the thorax, and then
again towards the abdomen. In less time than it takes to tell, the
murder is committed, and the Sphex, after setting her disordered
toilette to rights, prepares to carry off her victim, its limbs still
quivering in the death-throes. Let us reflect a moment on the admirable
tactics of which I have given a faint sketch. The Cerceris attacks a
passive adversary, incapable of flight, whose sole chance of safety is
found in a solid cuirass whose weak points the murderers know. But here
what a difference! The prey is armed with redoubtable mandibles,
capable of disembowelling the aggressor if they can seize her, and a
pair of strong feet, actual clubs, furnished with a double row of sharp
spines, which can be used alternatively to enable the cricket to bound
far away from an enemy or to overturn one by brutal kicks. Accordingly,
note what precautions on the part of the Sphex before using her dart.
The victim, lying on its back, cannot escape by using its hind levers,
for want of anything to spring from, as of course it would were it
attacked in its normal position, as are the big Weevils by Cerceris
tuberculata. Its spiny legs, mastered by the forefeet of the Sphex,
cannot be used as offensive weapons, and its mandibles, held at a
distance by the hind-feet of the Hymenopteron, open threateningly but
can seize nothing. But it is not enough for the Sphex to render it
impossible for her victim to hurt her: she must hold it so firmly
garrotted that no movement can turn the sting from the points where the
drop of poison must be instilled, and probably it is in order to hinder
any motion of the abdomen that one of the end segments is grasped. If a
fertile imagination had had free play to invent a plan of attack it
could not have devised anything better, and it is questionable whether
the athletes of the classic palestra when grappling an adversary would
have assumed attitudes more scientifically calculated.
I have just said that the dart is plunged several times into the
victim’s body, once under the neck, then behind the prothorax, lastly
near the top of the abdomen. It is in this triple blow that the
infallibility, the infused science of instinct, appear in all their
magnificence. First let us recall the chief conclusions to which the
preceding study of the Cerceris have led us. The victims of Hymenoptera
whose larva live on prey are not corpses, in spite of entire
immobility. There is merely total or partial paralysis, and more or
less annihilation of animal life, but vegetative life—that of the
nutritive organs—lasts a long while yet, and preserves from
decomposition the prey which the larvæ are not to devour for a
considerable time. To produce this paralysis the predatory Hymenoptera
use just those methods which the advanced science of our day might
suggest to the experimental physiologist—namely, wounding, by means of
a poisoned dart, those nervous centres which animate the organs of
locomotion. We know too that the various centres or ganglia of the
nervous chain in articulate animals act to a certain degree
independently, so that injury to one only causes, at all events
immediately, paralysis of the corresponding segment, and this in
proportion as the ganglia are more widely separated and distant from
each other. If, on the contrary, they are soldered together, injury to
the common centre causes paralysis of all the segments where its
ramifications spread. This is the case with Buprestids and Weevils,
which the Cerceris paralyses by a single sting, directed at the common
mass of the nerve centres in the thorax. But open a cricket, and what
do we find to animate the three pairs of feet? We find what the Sphex
knew long before the anatomist, three nerve centres far apart. Thence
the fine logic of the three stabs. Proud science! humble thyself.
Crickets sacrificed by Sphex flavipennis are no more dead, in spite of
all appearances, than are Weevils struck by a Cerceris. The flexibility
of the integuments displays the slightest internal movement, and thus
makes useless the artificial means used by me to show some remains of
life in the Cleonus of Cerceris tuberculata. If one closely observes a
cricket stretched on its back a week or even a fortnight or more after
the murder, one sees the abdomen heave strongly at long intervals. Very
often one can notice a quiver of the palpi and marked movements in the
antennæ and the bands of the abdomen, which separate and then come
suddenly together. By putting such crickets into glass tubes I have
kept them perfectly fresh for six weeks. Consequently, the Sphex larvæ,
which live less than a fortnight before enclosing themselves in their
cocoons, are sure of fresh food as long as they care to feast.
The chase is over; the three or four crickets needed to store a cell
are heaped methodically on their backs, their heads at the far end,
their feet toward the entrance. An egg is laid on each. Then the burrow
has to be closed. The sand from the excavation lying heaped before the
cell door is promptly swept out backward into the passage. From time to
time fair-sized bits of gravel are chosen singly, the Sphex scratching
in the fragments with her forefeet, and carrying them in her jaws to
consolidate the pulverised mass. If none suitable are at hand, she goes
to look for them in the neighbourhood, apparently choosing with such
scrupulous care as a mason would show in selecting the best stones for
a building. Vegetable remains and tiny bits of dead leaf are also
employed. In a moment every outward sign of the subterranean dwelling
is gone, and if one has not been careful to mark its position, it is
impossible for the most attentive eye to find it again. This done, a
new burrow is made, provisioned and walled up as soon as the Sphex has
eggs to house. Having finished laying, she returns to a careless and
vagabond life until the first cold weather ends her well-filled
existence.
The Sphex’s task is accomplished. I will finish mine by an examination
of her weapon. The organ destined for the elaboration of her poison is
composed of two elegantly branched tubes communicating separately with
a common reservoir or pear-shaped vial, whence proceeds a slender
channel leading to the axis of the sting and conducting to its end the
little poisoned drop. The dart is extremely small, and not such as one
would expect from the size of the Sphex, especially from the effect
which her sting produces on crickets. The point is quite smooth,
without the barbs found in the sting of the hive bee. The reason of
this is evident. The bee uses her sting to avenge an injury only at the
cost of life, the barbs preventing its withdrawal from the wound, and
thus causing mortal ruptures in the viscera at the end of the abdomen.
What could the Sphex have done with a weapon which would have been
fatal the first time it was used? Even supposing that the barbed dart
could have been withdrawn, I doubt if any Hymenopteron using its
weapon, especially to wound game destined for its progeny, would be
provided with one. For here the dart is not a fine gentleman’s weapon,
unsheathed for vengeance, which is said to be the pleasure of the gods,
but a very costly one, since the vindictive bee sometimes pays for it
with life. It is a worker’s tool, on which depends the future of the
larvæ, thus it should be one easily used in a struggle with captured
prey, plunging into and coming out of the flesh without any delay—a
condition much better fulfilled by a smooth blade than by a barbed one.
I wished to ascertain at my own expense if the Sphex’s sting be very
painful—that sting which knocks over robust victims with frightful
rapidity. Well, I own with great admiration that it is slight and
cannot be at all compared as to pain with those of the bee and the
irascible wasp. It hurts so little that, instead of using pincers, I
never hesitated to catch with my fingers any Sphegidæ which I wanted
for my researches. I may say the same of the various Cerceris,
Philanthides, Palares, and even of the huge Scoliides, whose very look
is terrifying, and in general of all predatory Hymenoptera which I have
been able to observe. I except, however, those that hunt spiders, the
Pompili, and even their sting is far less severe than that of a bee.
One last remark. We know how furiously Hymenoptera armed with a sting
used only for defence rush at the bold man who disturbs their nest, and
punish his temerity. Those on the contrary whose sting is used only for
hunting are very pacific, as if they guessed how important for their
family is the little poison drop in their vase. That droplet is the
safeguard of their race—I might really say their means of subsistence;
therefore they use it economically, in the serious business of the
chase, with no parade of vengeful courage. I was not once punished by a
sting when I established myself amid colonies of our various predatory
Hymenoptera, whose nests I overturned, carrying off larvæ and
provisions. To induce the creature to use its weapon, one must lay hold
of it, and even then the skin is not always pierced, unless one puts
within reach a part more delicate than the fingers, such as the wrist.