THE YELLOW-WINGED SPHEX
Under their powerful armour, which no dart can penetrate, the insects
of the Beetle tribe offer but a single vulnerable spot to the
sting-bearing enemy. This defect in the breastplate is known to the
murderess, who drives in her poisoned dagger there and at one blow
strikes the three motor centres, for she selects her victims from the
Weevil and Buprestis families, whose nervous system is centralized to
the requisite degree. But what will happen when the prey is an insect
clad not in mail but in a soft skin, which the Wasp can stab here or
there indifferently, in any part of the body that chances to be
exposed? In that case are the blows still delivered scientifically?
Like the assassin who strikes at the heart to cut short the dangerous
resistance of his victim, does the assailant follow the tactics of the
Cerceres and wound the motor ganglia by preference? If that be so, then
what happens when these ganglia are some distance apart and so
independent in their action that paralysis of one is not necessarily
followed by paralysis of the others? These questions will be answered
by the story of a Cricket-huntress, the Yellow-winged Sphex (Sphex
flavipennis).
It is at the end of July that the Yellow-winged Sphex tears the cocoon
that has protected her until then and flies out of her subterranean
cradle. During the whole of August she is frequently seen flitting, in
search of some drop of honey, around the spiked heads of the field
eryngo, the commonest of the hardy plants that brave the heat of the
dog-days in this month. But this careless life does not last long, for
by the beginning of September the Sphex is at her arduous task as a
sapper and huntress. She generally selects some small plateau, on the
high banks by the side of the roads, wherein to establish her home,
provided that she find two indispensable things there: a sandy soil,
easy to dig; and sunshine. No other precaution is taken to protect the
dwelling against the autumn rains or winter frosts. A horizontal site,
unprotected, lashed by the rain and the winds, suits her perfectly, on
condition, however, that it is exposed to the sun. And, when a heavy
shower comes in the middle of her mining, it is pitiful next day to see
the half-built galleries in ruins, choked with sand and finally
abandoned by their engineers.
The Sphex seldom practises her industry alone; the site selected is
usually exploited by small bands of ten or twenty sappers or more. One
must have spent days in contemplating one of these villages to form any
idea of the restless activity, the spasmodic haste, the abrupt
movements of those hard-working miners. The soil is rapidly attacked
with the rakes of the forefeet: canis instar, as Linnæus says. No
mischievous puppy displays more energy in digging up the ground. At the
same time, each worker sings her glad ditty, which consists of a shrill
and strident noise, constantly broken off and modulated by the
vibrations of the wings and thorax. One would think that they were a
troop of merry companions encouraging one another in their work with a
cadenced rhythm. Meanwhile the sand flies, falling in a fine dust on
their quivering wings; and the too bulky gravel, removed bit by bit,
rolls far away from the workyard. If a piece seems too heavy to be
moved, the insect gets up steam with a shrill note which reminds one of
the woodman’s ‘Hoo!’ Under the redoubled efforts of tarsi and mandibles
the cave soon takes shape; the insect is already able to dive into it
bodily. We then see a lively alternation of forward movements, to
loosen new materials, and backward movements, to sweep the rubbish
outside. In this constant hurrying to and fro the Sphex does not walk,
she darts as though shot from a spring; she bounds with throbbing
abdomen and quivering antennæ, her whole body, in short, animated with
a musical vibration. The miner is now out of sight; but we still hear
underground her untiring song, while at intervals we catch a glimpse of
her hind-legs, pushing a torrent of sand backwards to the mouth of the
burrow. From time to time the Sphex interrupts her subterranean
labours, either to come and dust herself in the sun, to rid herself of
the grains of sand which, slipping into her delicate joints, might
hamper the liberty of her movements, or else to reconnoitre the
neighbourhood. Despite these interruptions, which for that matter do
not last long, the gallery is dug in the space of a few hours; and the
Sphex comes to her threshold to chant her triumph and give the
finishing polish to her work by removing some unevenness and carrying
away a speck or two of earth whose drawbacks are perceptible to her
discerning eye alone.
Of the numerous tribes of Sphex-wasps which I have visited, one in
particular remains fixed in my memory because of its curious
dwelling-place. On the edge of a high-road were some small heaps of
mud, taken from the ditches by the road-mender’s shovel. One of these
heaps, long ago dried in the sun, formed a cone-shaped mound,
resembling a large sugar-loaf twenty inches high. The site seemed to
have attracted the Wasps, who had established themselves there in a
more populous colony than I have ever since beheld. The cone of dry mud
was riddled from top to bottom with burrows, which gave it the
appearance of an enormous sponge. On every storey there was a feverish
animation, a busy coming and going which reminded one of the scenes in
some great yard when the work is urgent. Crickets were being dragged by
the antennæ up the slopes of the conical city; victuals were being
stored in the larders of the cells; dust was pouring from the galleries
in process of excavation by the miners; grimy faces appeared at
intervals at the mouths of the tunnels; there were constant exits and
constant entrances; and now and again a Sphex, in her brief intervals
of leisure, would climb to the top of the cone, perhaps to cast a look
of satisfaction from this belvedere over the works in general. What a
spectacle to tempt me, to make me long to carry the whole city and its
inhabitants away with me! It was useless even to try: the mass was too
heavy. One cannot root up a village from its foundations to transplant
it elsewhere.
We will return, therefore, to the Sphex-wasps working on level ground,
in ordinary soil, as happens in by far the greater number of cases. As
soon as the burrow is dug, the chase begins. Let us profit by the
Wasp’s distant excursions in search of her game and examine the
dwelling. The usual site of a Sphex colony is, as I said, level ground.
Nevertheless, the soil is not so smooth but that we find a few little
mounds crowned with a tuft of grass or wormwood, a few cracks
consolidated by the scanty roots of the vegetation that covers them. It
is in the sides of these furrows that the Sphex builds her dwelling.
The gallery consists first of a horizontal portion, two or three inches
long and serving as an approach to the hidden retreat destined for the
provisions and the larvæ. It is in this entrance-passage that the Sphex
takes shelter in bad weather; it is here that she retires for the night
and rests for a few moments in the daytime, putting outside only her
expressive face, with its great, bold eyes. Following on the vestibule
comes a sudden bend, which descends more or less obliquely to a depth
of two or three inches more and ends in an oval cell of somewhat larger
diameter, whose main axis lies horizontally. The walls of the cell are
not coated with any particular cement; but, in spite of their bareness,
we can see that they have been the object of the most conscientious
labour. The sand has been heaped up and carefully levelled on the
floor, the ceiling and the sides, so as to prevent landslips and remove
any roughness that might hurt the delicate skin of the grub. Lastly,
this cell communicates with the passage by a narrow entrance, just wide
enough to admit the Sphex laden with her prey.
When this first cell is supplied with an egg and the necessary
provisions, the Sphex walls up the entrance, but does not yet abandon
her burrow. A second cell is dug beside the first and victualled in the
same way; then a third and sometimes a fourth. Not till then does the
Sphex shoot back into the burrow all the rubbish accumulated outside
the door and completely remove all the outward traces of her work.
Thus, to each burrow there are usually three cells, rarely two and
still more rarely four. Now, as we ascertain when dissecting the
insect, we can estimate the number of eggs laid at about thirty, which
brings up to ten the number of burrows needed. On the other hand, the
operations are hardly begun before September and are finished by the
end of the month. The Sphex, therefore, can devote only two or three
days at most to each burrow and its provisioning. No one will deny that
the active little creature has not a moment to lose, when, in so short
a time, she has to excavate her den, to procure a dozen Crickets, to
carry them sometimes from a distance in the face of innumerable
difficulties, to store them away and finally to stop up the burrow.
And, besides, there are days when the wind makes hunting impossible,
rainy days or even merely grey days, which cause all work to be
suspended. One can readily imagine from this that the Sphex is unable
to give to her buildings the perhaps permanent solidity which the Great
Cerceres bestow upon their long galleries. The latter hand down from
generation to generation their substantial dwellings, each year
excavated to a greater depth than the last, galleries which threw me
into a sweat when I tried to inspect them and which generally triumphed
over my efforts and my implements. The Sphex does not inherit the work
of her predecessors: she has to do everything for herself and quickly.
Her dwelling is but a tent, hastily pitched for a day and shifted on
the morrow. As compensation, the larvæ, who have only a thin layer of
sand to cover them, are capable themselves of providing the shelter
which their mother could not create: they clothe themselves in a
threefold and fourfold waterproof wrapper, far superior to the thin
cocoon of the Cerceres.
But here, with a loud buzz, comes a Sphex who, returning from the
chase, stops on a neighbouring bush, holding in her mandibles, by one
antenna, a large Cricket, several times her own weight. Exhausted by
the burden, she takes a moment’s rest. Then she once more grips her
captive between her feet and, with a supreme effort, covers in one
flight the width of the ravine that separates her from her home. She
alights heavily on the level ground where I am watching, in the very
middle of a Sphex village. The rest of the journey is performed on
foot. The Wasp, not at all intimidated by my presence, bestrides her
victim and advances, bearing her head proudly aloft and hauling the
Cricket, who trails between her legs, by an antenna held in her
mandibles. If the ground be bare, it is easy to drag the victim along;
but, should some grass-tuft spread the network of its shoots across the
road, it is curious to observe the amazement of the Sphex when one of
these little ropes suddenly thwarts her efforts; it is curious to
witness her marches and counter-marches, her reiterated attempts, until
the obstacle is overcome, either with the aid of the wings or by means
of a clever deviation. The Cricket is at last conveyed to his
destination and is so placed that his antennæ exactly touch the mouth
of the burrow. The Sphex then abandons her prey and descends hurriedly
to the bottom of the cave. A few seconds later we see her reappear,
showing her head out of doors and giving a little cry of delight. The
Cricket’s antennæ are within her reach; she seizes them and the game is
brought quickly down to the lair.
I still ask myself, without being able to find a sufficiently
convincing solution, the reason for these complicated proceedings at
the moment when the Cricket is introduced into the burrow. Instead of
going down to her den alone, to reappear afterwards and pick up the
prey left for a time on the threshold, would not the Sphex have done
better to continue to drag the Cricket along the gallery as she does in
the open air, seeing that the width of the tunnel permits it, or else
to go in first, backwards, and pull him after her? The various
Predatory Wasps whom I have hitherto been able to observe carry down to
their cells straight away, without preliminaries, the game which they
hold clasped beneath their bellies with the aid of their mandibles and
their middle-legs. Léon Dufour’s Cerceris begins by complicating her
procedure, because, after laying her Buprestis for a moment at the door
of her underground home, she at once enters her gallery backwards and
then seizes the victim with her mandibles and drags it to the bottom of
the burrow. But it is a far cry from these tactics and those adopted in
a like case by the Cricket-hunters. Why that domiciliary visit which
invariably precedes the entrance of the game? Could it not be that,
before descending with a cumbrous burden, the Sphex thinks it wise to
take a look at the bottom of her dwelling, so as to make sure that all
is well and, if necessary, to drive out some brazen parasite who may
have slipped in during her absence? If so, who is the parasite? Several
Diptera, Predatory Gnats, especially Tachinæ, watch at the doors of the
Hunting Wasps, spying for the propitious moment to lay their eggs on
others’ provisions; but none of them enters the home or ventures into
the dark passages where the owner, if by ill-luck she happened to be
in, would perhaps make them pay dearly for their audacity. The Sphex,
like all the rest, pays her tribute to the plundering Tachinæ; but
these never enter the burrow to perpetrate their misdeeds. Besides,
have they not all the time that they need to lay their eggs on the
Cricket? If they are sharp about it, they can easily profit by the
temporary abandonment of the victim to entrust their progeny to it.
Some greater danger still must therefore threaten the Sphex, since her
preliminary descent of the burrow is of such imperious necessity.
Here is the only fact observed by myself that may throw a little light
on the problem. Amid a colony of Sphex-wasps in full swing, a colony
from which any other Wasp is usually excluded, I one day surprised a
huntress of a different genus, Tachytes nigra, carrying one by one,
without hurrying, in the midst of the crowd where she was but an
intruder, grains of sand, bits of little dry stalks and other
diminutive materials to stop up a burrow of the same shape and width as
the adjacent burrows of the Sphex. The labour was too carefully
performed to allow of any doubt of the presence of the worker’s egg in
the tunnel. A Sphex moving about uneasily, apparently the lawful owner
of the burrow, did not fail, each time that the strange Wasp entered
the gallery, to rush in pursuit of her; but she emerged swiftly, as
though frightened, followed by the other, who impassively continued her
work. I inspected this burrow, evidently an object in dispute between
the two Wasps, and found in it a cell provisioned with four Crickets.
Suspicion almost makes way for certainty: these provisions are far in
excess of the needs of a Tachytes-grub, who is certainly not more than
half the size of the larva of the Sphex. She whose impassiveness, whose
care to stop up the burrow would at first have made one take her for
the mistress of the house, was in reality a mere usurper. How is it
that the Sphex, who is larger and more powerful than her adversary,
allows herself to be robbed with impunity, confining herself to
fruitless pursuits and fleeing like a coward when the interloper, who
does not even appear to notice her presence, turns round to leave the
burrow? Can it be that, in insects as in man, the first chance of
success lies in de l’audace, encore de l’audace et toujours de
l’audace? The usurper certainly had audacity and to spare. I see her
still, with imperturbable calmness, moving in and out in front of the
complaisant Sphex, who stamps her feet with impatience but does not
fall upon the thief.
I will add that, in other circumstances, I have repeatedly found the
same Wasp, whom I presume to be a parasite, in short the Black
Tachytes, dragging a Cricket by one of his antennæ. Was he a
lawfully-acquired prey? I should like to think so; but the vacillating
behaviour of the insect, who went straying about the ruts in the roads
as though seeking for a burrow to suit it, always left me uncertain. I
have never witnessed its digging-work, if it really undertakes the
labour of excavation. And, a more serious matter, I have seen it leave
its game on the rubbish-heap, perhaps not knowing what to do with it,
for lack of a burrow wherein to place it. Such wastefulness as this
seems to me to point to ill-gotten goods; and I ask myself if the
Cricket were not stolen from the Sphex at the moment when she abandoned
her prey on the threshold. My suspicions also fall upon Tachytes
obsoleta, banded with white round the abdomen like Sphex albisecta and
feeding her larvæ on Crickets similar to those hunted by the latter. I
have never seen her digging any galleries, but I have caught her with a
Cricket whom the Sphex would not have rejected. This identity of
provisions in species of different genera raises doubts in my mind as
to the lawfulness of the booty. Let me add, lastly, to atone in a
measure for the injury which my suspicions may do to the reputation of
the genus, that I have been the eye-witness of a perfectly
straightforward capture of a small and still wingless Cricket by
Tachytes tarsina and that I have seen her digging cells and victualling
them with game acquired by her own valiant exertions.
I have therefore only suspicions to offer in explanation of the
obstinacy of the Sphex-wasps in going down their tunnels before
carrying in their prey. Can they have some other object besides that of
dislodging a parasite who may have arrived during their absence? This
is what I despair of ever knowing; for who can interpret the thousand
ruses of instinct? Poor human reason, which cannot even fathom the
wisdom of a Sphex!
At any rate, it has been proved that these ruses are singularly
invariable. In this connection I will mention an experiment which
interested me greatly. Here are the particulars: at the moment when the
Sphex is making her domiciliary visit, I take the Cricket left at the
entrance to the dwelling and place her a few inches farther away. The
Sphex comes up, utters her usual cry, looks here and there in
astonishment, and, seeing the game too far off, comes out of her hole
to seize it and bring it back to its right place. Having done this, she
goes down again, but alone. I play the same trick upon her; and the
Sphex has the same disappointment on her arrival at the entrance. The
victim is once more dragged back to the edge of the hole, but the Wasp
always goes down alone; and this goes on as long as my patience is not
exhausted. Time after time, forty times over, did I repeat the same
experiment on the same Wasp; her persistency vanquished mine and her
tactics never varied.
Having demonstrated the same inflexible obstinacy which I have just
described in the case of all the Sphex-wasps on whom I cared to
experiment in the same colony, I continued to worry my head over it for
some time. What I asked myself was this:
‘Does the insect obey a fatal tendency, which no circumstances can ever
modify? Are its actions all performed by rule; and has it no power of
acquiring the least experience on its own account?’
Some additional observations modified this too absolute view. Next year
I visit the same spot at the proper season. The new generation has
inherited the burrowing-site selected by the previous generation; it
has also faithfully inherited its tactics: the experiment of
withdrawing the Cricket yields the same results. Such as last year’s
Sphex-wasps were, such are those of the present year, equally
persistent in a fruitless procedure. The illusion was simply growing
worse, when good fortune brought me into the presence of another colony
of Sphex-wasps, in a district at some distance from the first. I
recommenced my attempts. After two or three experiments with results
similar to those which I had so often obtained, the Sphex got astride
of the Cricket, seized him with her mandibles by the antennæ, and at
once dragged him into the burrow. Who was the fool now? Why, the
experimenter foiled by the clever Wasp! At the other holes, her
neighbours likewise, one sooner, another later, discovered my treachery
and entered the dwelling with the game, instead of persisting in
abandoning it on the threshold to seize it afterwards. What did all
this mean? The colony which I was now inspecting, descended from
another stock—for the children return to the site selected by their
parents—was cleverer than the colony of the year before. Craft is
handed down: there are tribes that are sharper-witted and tribes that
are duller-witted, apparently according to the faculties of their
elders. With the Sphex as with us, the intellect differs with the
province.
Next day, in a different locality, I repeated my experiment with
another Cricket; and every time the Sphex was hoodwinked. I had come
upon a dense-minded tribe, a regular village of Bœotians, as in my
first observations.