THE NEST-BUILDING ODYNERUS
If further proofs than those submitted elsewhere were needful, to
demonstrate that the organ does not imply the function, that the
implement does not determine the work, [57] the Odynerus group would
furnish us with very remarkable evidence. With a close similarity of
organization, not only in the details but also in the aggregate, a
similarity which makes these insects one of the most natural genera in
respect of structure, they possess a great variety of industries,
bearing no relation one to the other, though carried on with the same
equipment. Apart from the likeness in form, one single characteristic
unites this group, whose habits are so unlike: all the Odyneri are
game-hunters; they victual their families with grubs paralysed with the
sting, with little caterpillars and small Beetle-larvæ.
But to achieve this common end, the larder furnished with its egg and
stuffed with game, how many several methods of construction! If we were
better-acquainted with the biology of the genus, we should perhaps find
architects of almost as many different schools as there are species. My
investigations, which were dependent on opportunity, have as yet borne
upon only three of the Odyneri; and these three, with the same
implement, the curved, toothed pincers of their mandibles, apply
themselves to the most dissimilar industries.
One of them, O. reniformis, whose work I have described in an earlier
chapter, digs a deep gallery in a hard soil and with the rubbish
constructs, at the mouth of her well, a sort of curved chimney, with a
guilloche pattern, the materials of which are afterwards again employed
to close the abode. Formerly, when I made her acquaintance in front of
a steep loamy bank baked by the sun, I whiled away the long hours of
waiting by conversing, turn and turn about, with the Hoopoe, who taught
me how to pronounce Latin, and with my Dog, who, lying in the shade of
a leafy thicket, cooling his belly in the moist sand, taught me how to
practise patience. The Wasp was rare and by no means prodigal of her
returns to the nest where I was watching her skilful tactics. Nowadays,
every spring, I have a populous colony of her before my eyes in one of
the paths of my enclosure. When the period for the works arrives, I
surround the hamlet with stakes to mark the site, lest heedless
footsteps should destroy the pretty chimneys built of grains of earth.
The second, O. alpestris, Sauss., is by trade a resin-worker.
Possessing the same tool as her colleague the miner, but not the same
skill, she does not dig herself a dwelling; she prefers to settle down
in borrowed lodgings provided by an empty Snail-shell. The shells of
Helix nemoralis, of H. aspersa, [58] when very incompletely developed,
and of Bulimulus radiatus are the only dwellings that I have known her
to occupy and also the only ones that would serve her turn under the
stone-heaps where, in company with Anthidium bellicosum, she performs
her labours in July and August.
Saved by the Snail from the hard task of excavation, she specializes in
mosaic and produces a work of art which is superior in elegance to the
miner’s temporary guilloche. Her materials are, on the one hand, resin;
on the other, little bits of gravel. Her method is very unlike that of
the two resin-workers who find a lodging in the shell of the Edible
Snail. These two swamp with gum, on the outer surface of the lid, their
coarse, angular bricks, which are unequal in size, variable in nature
and often of a half-earthy character, so that the unevenness of the
work, in which the pieces are laid side by side at random, is hidden
under a coat of resin. On the inner surface the gum does not fill the
gaps and the cemented fragments appear with all their irregular
projections and their clumsy arrangement. Remember also that the bits
of gravel are kept exclusively for the operculum, or lid, the final
covering; the partitions which mark off the cells are made entirely of
resin, without any mineral particles.
The Alpine Odynerus works on a different plan: she saves pitch by
making better use of stone. A number of round, flinty atoms are set in
a bed of still sticky cement, on the outer surface. They fit one
against the other, are almost all of the same size, that of a pin’s
head, and are selected singly by the artist amid the miscellaneous
rubbish that litters the ground. When it is well-executed, as is
frequently the case, the result suggests a piece of embroidery worked
with roughly-fashioned beads of quartz. The Anthidia of the
Snail-shell, rude labourers that they are, accept all that falls to
their mandibles: angular splinters of limestone, morsels of flint, bits
of shell, hard particles of earth; the daintier Odynerus as a rule
inlays with beads of flint only. Can this taste for gems be due to the
brilliancy, the translucency, the polish of the grain? Can it be that
the insect takes pleasure in its casket of precious stones? The answer
will be the same as in the case of the ornamental rose-window, the tiny
shell sometimes inserted in the centre of the lid by the two
resin-gatherers who inhabit the shell of the Edible Snail: why not?
Be this as it may, the gem-collector is so pleased with her pretty
pebbles that she puts them everywhere. The partitions that subdivide
the shell into chambers are reproductions of the lid: each has a
carefully-finished mosaic of translucent flints on the front surface.
In this manner three or four cells are contrived in the shell of the
Edible Snail; in that of the Bulimulus, two at most. The cells are
small but correctly shaped and strongly protected.
The protection, for that matter, is not restricted to these multiple
paved hangings: if you hold the Snail-shell to your ear and shake it,
you hear a rattle of stones. The Odynerus, in fact, is as familiar as
the Anthidia with the art of fortification by means of barricades. I
make a breach in the side of the Snail-shell and pour out the heap of
loose gravel that blocks the vestibule between the last partition and
the lid. One detail should be noted: the materials which I collect are
not homogeneous. Small polished pebbles predominate, but they are mixed
with fragments of coarse limestone, bits of shell and particles of
earth. The Odynerus, so fastidious in choosing the flint for her
mosaics, employs for her filling the first rubbish that comes to hand.
Even so do the two resin-gatherers act when barricading their
Snail-shells. As a conscientious historian, I will add that the
incoherent heap of rubbish is not always there: another point of
resemblance with the practice of the Anthidia.
To my great regret, I can carry the biography of the Alpine Odynerus no
farther. The insect appears to me to be very rare. I come upon its nest
at long intervals in winter, the only season propitious to laborious
searches in the stone-heaps. With the dwelling and its inhabitant,
hatched in my specimen-jars, I am familiar; but the egg, the larva and
the provisions I do not know.
In compensation, I possess all the details that could be desired about
the third species, O. nidulator, Sauss. This insect, like the just
mentioned, is ignorant of the art of laying the foundations of its
abode and demands a ready-made lodging. Like the Osmiæ, the Megachiles
and the cotton-spinning Anthidia, it wants a cylindrical gallery,
either natural or excavated by miners. Its art consists in partitioning
a tunnel and subdividing it into chambers: plasterer’s art, in short.
Here then, in three species, the only ones whose habits I have had the
opportunity of learning, we see three very different trades: the
miner’s, the resin-worker’s and the plasterer’s. In these three guilds
I find exactly the same equipment of tools; and I defy the most
meticulous magnifying-glass to tell us what organic modification
suggests to the one insect the pavement of pebbles upon a bed of resin,
to the second the mine-shaft with its guilloched chimney, to the third
the alien cylinder, partitioned with mud. No and again no: the organ
does not constitute the function, the tool does not make the workman.
With similar implements, the Odynerus group executes the most
dissimilar tasks, because each species has its predetermined skill, its
art that governs the tool and is not governed by it. How plainly this
conclusion would appear had I been privileged to review the entire
Odynerus genus! How many industries remain for us to see, with the tool
undergoing no modification! I suggest investigations on these lines to
whomsoever it may concern, were it only in order to shed a little light
upon this numerous and difficult group, of which the future will, I
trust, give us a lucid classification based upon its industrial guilds.
Let us leave these generalities and pass to the detailed story of the
Nest-building Odynerus. There are few Wasps with whose private life I
am better acquainted; and I owe this abundant information to
circumstances which, for me, impart a double value to the facts,
because of the pleasant memories evoked. I had often extracted the
Nest-building Odynerus’ series of cells from the old galleries of the
Anthophoræ; I knew that the insect occupies dwellings not dug with its
own mandibles and that its labours are confined to the partitions; I
knew its yellow larva and its slender, amber-hued cocoon. I knew
nothing of all the rest, when I received from my daughter Claire a
bundle of reed-cuttings which filled me with exultation.
Brought up in a zoological house, the dear child has retained a vivid
memory of our evening talks, in which the insect so often cropped up;
and her discerning eye is able quickly to distinguish, amid her casual
discoveries, anything that may assist me in my studies of instinct. Her
country home, in the neighbourhood of Orange, boasts a rustic
poultry-house constructed partly of reeds laid in horizontal stages. In
the middle of June last year (1889), she noticed, when visiting her
Hens, certain Wasps making their way in large and busy numbers into the
cut reeds, coming out again and soon returning laden with a load of
earth or some malodorous little grub. Her attention once aroused, the
rest did not take long: she had discovered a magnificent subject for me
to study. That very evening I received a bundle of reeds, with a letter
giving me circumstantial details.
The Wasp, as Claire called it and as Réaumur named it of old, when
speaking of a species of the same genus but of very different habits,
the Wasp, so the letter told me, hoards in her nests a dumpy head of
game, covered with black spots and smelling strongly of bitter almonds.
I informed my daughter that this game was the larva of the Poplar
Leaf-beetle (Chrysomela populi), a Beetle with red wing-cases reminding
one, on a larger scale, of the Coccinella, or Common Ladybird. Insect
and larva should be found together on the poplars of the neighbourhood,
browsing promiscuously on the leaves. I added that a glorious
opportunity had presented itself and that we must profit by it without
delay. She therefore received instructions to keep a watch on this,
that and the other and to furnish my insect laboratory with reed-stumps
as and when they became colonized and with poplar-branches covered with
Chrysomela-grubs. A collaboration was thus set up between Orange and
Sérignan, the facts observed on both sides mutually completing and
corroborating each other.
Let us come quickly to the bundle of reeds, the first examination of
which gratifies my fondest hopes. It contains things that reawaken all
the enthusiasm of my youth: cells converted into game-baskets, eggs on
the point of hatching beside the victuals, new-born grubs biting into
their first victim, larvæ of fuller growth, weavers at work on their
cocoons, in fact everything that one could wish for. Never, except with
the Scoliæ in my heap of garden-mould, [59] has fortune served me
better. Let us make an orderly inventory of these rich documents.
Already various Bees that favour borrowed houses have shown us the
insect discriminating between one dwelling and another and selecting
the best to make their homes in. We now have a predatory Wasp who,
following the example of the Osmiæ, the Leaf-cutters and the
Cotton-bees, leaves the ancestral cabin for the cylinder of the reed,
to which man’s pruning-knife has prepared the access. The natural
shelter, of indifferent quality, is succeeded by the artificial and
more convenient refuge. The Odynerus’ primitive lodging is the
abandoned corridor of the Anthophora, or any other burrow dug in the
earth by no matter what miner. The wooden tube, free from damp and
bathed in sunshine, is recognized as preferable; and the insect hastens
to adopt it when the opportunity occurs. The tunnel of the reed must be
recognized as an excellent habitation, superior to all others, for
never outside any abode of Anthophoræ have I seen a colony of Odyneri
so populous as that of the Orange poultry-house.
The reeds invaded are laid horizontally, a condition on which the Bees
likewise insist, if only to shelter from the rain the house-door,
plugged with pervious materials, such as mud, cotton, or round, leafy
disks. Their inner diameter attains an average of two-fifths of an
inch. The length occupied by the cells varies greatly. Sometimes the
Odynerus takes possession only of that fragment of the interval between
two knots which the stroke of the pruning-knife has left free, a
fragment longer or shorter according to the chances of the cutting. In
that case, a small number of cells is enough to fill the available
space. But generally, if the stump be too short and not worth the
trouble of working, the insect bores through the partition at the end
and thus adds a complete internode to the vestibule with the open
entrance. In a lodging of this kind, some eight inches long, the number
of chambers will amount to fourteen or fifteen.
In thus enlarging the house by removing a floor, the Odynerus displays
two separate talents, the plasterer’s and the carpenter’s. Her knack
for wood-working, moreover, is extremely useful in another
circumstance, as we shall see. The Three-horned Osmia, also an
enthusiastic partitioner of reeds, does not employ this means of
obtaining a spacious lodging at small cost. I find that she always
leaves the first party-wall intact, building the row of cells against
it, however short the section may be. To make an opening in a slight
barrier is not one of her methods. She could do it if she wished; for
to gnaw through the ceiling of the cell on hatching and then through
the general door of the nest is a more difficult job. She possesses in
her mandibles a tool powerful enough for the purpose; but she is not
aware that a splendid gallery lies beyond the obstacle. How did the
Odynerus learn, if she did not know from the beginning, what the Osmia,
with her greater experience of the reed, does not know?
Apart from the ingenious device of breaking down the party-wall in
order to enlarge the premises, the Odynerus is the Osmia’s equal as a
plasterer and partition-builder. The results of the two industries
resemble each other so closely that we should easily confuse them if we
merely examined the structure. We find in both cases, at irregular
intervals, the same partitions, the same round disks of fine earth, of
mud gathered wet on the brink of an irrigation-ditch or stream. Judging
from the appearance of the materials, I imagine that the Odynerus has
fetched her clay from the banks of the neighbouring torrent, the
Aygues.
Identity of construction is maintained even in details which I had at
first regarded as a feat peculiar to the Osmia. Let us recall her
compartment-building secret. If the reed be of middling diameter, the
cell is first stocked with provisions and next bounded in front with a
partition run up then and there, without any pause in its construction.
If the reed, without being excessively wide, be of a certain thickness,
the Osmia, before stowing away the victuals, gets to work on the front
partition, providing it with an opening at the side, a sort of
service-hatch, through which the honey is more easily discharged and
the egg more easily placed in position. Well, this secret of the
service-hatch, which was revealed to me by the glass tube, is as
well-known to the Odynerus as to the Osmia. She, too, in the bigger
reeds, finds it to her advantage to close the larder in front before
bringing the game; she shuts the cell with a door provided with a sort
of wicket, through which the victualling and the laying are done. When
everything is finished inside, a plug of mortar closes the hatch.
I did not of course see the Odynerus working at her partition with its
wicket-door, as I saw the Osmia performing in my glass tubes; but the
work itself speaks quite plainly of the method followed. In the centre
of the partitions in the medium reeds there is nothing in particular to
be seen; in the centre of the partitions in the larger reeds there is a
circular aperture, afterwards filled with a plug, which always differs
from the rest of the partition by projecting inwards and sometimes
differs in colour. The thing is obvious: the small partitions are made
in one spell, whereas the work on the larger ones is interrupted and
then resumed.
As we see, it would be pretty difficult to distinguish the Odynerus’
nest from the Osmia’s, if our enquiries were confined to the cells. One
characteristic, however, and not the least curious enables an attentive
eye to tell the owner without opening the reed. The Osmia closes her
dwelling with a thick plug of earth similar in nature to that employed
for the partitions. The Odynerus, it goes without saying, does not
neglect this means of defence: she, too, makes a solid stopper; but to
the unsophisticated method of the Osmia she adds the resources of a
more highly-finished art. Over her earthen stopper, a thing liable to
be spoilt by frost and damp, she spreads, on the outside, a good thick
layer of a composition of clay and chopped-up woody fibres. It matches
the red wax with which we seal the corks of our bottles.
These fibres, which resemble the remains of a coarse tow retted by long
exposure to the air, I should be inclined to look upon as taken from
reeds spoilt by the rain and bleached by the sun. The Odynerus planes
them off in shavings, which she afterwards crumbles by chewing them.
This is how the Common Wasps and the Polistes work on soft dead wood,
when gathering the raw material for their brown paper. But the
reed-dweller, who has no intention of employing her scrapings for
paper-making, does not cut up these fibrous particles anything like so
finely. She contents herself with breaking them up and unravelling them
a little. Mixed with thick mud, the same as that of the partitions and
the final plug, they make an excellent loam, which is far less liable
to go to pieces than unmixed clay would be. The efficacy of this
ingenious stucco is evident. After some months of exposure to the
inclemencies of the weather, the Osmia’s door, made of earth only, is
very much dilapidated, whereas the Odynerus’ door, covered on the
outside with a layer of fibrous composition, remains intact. Let us
credit the Odynerus with inventing and patenting the loam covering and
proceed.
After the nest, the victuals. One sort of game alone is served to the
Odynerus’ family: this is the larva of the Poplar Leaf-beetle
(Chrysomela populi, Lina p.), a larva which, in company with the adult
insect, ravages the poplar-leaves at the end of spring. Consulted
merely by our taste, the Odynerus’ game is anything but enticing in
shape and still less in smell. It is a plump, thickset grub, with a
bare, flesh-white skin covered with several lines of glossy black dots.
The abdomen, in particular, has thirteen rows of these black spots,
namely, four on the top, three on each side and three underneath. The
four dorsal rows vary in structure: the two in the middle consist of
plain black specks; those on either side consist of little pimples,
each shaped like a truncated cone with a minute opening at the top. One
of these cones rises on the right and left of each abdominal segment,
except the last two; there is also one on the right and one on the left
of the metathorax and mesothorax. These two are larger than the others.
There are nine pairs of perforated pimples in all.
If we tease the creature, we see welling up from the bottom of these
several little craters an opalescent liquid, which runs and spreads all
over the larva. It has a strong smell of bitter almonds, or rather of
nitrobenzene, commonly known as essence of mirbane, a powerful and most
repulsive smell. The discharge of this substance is a means of defence.
We have only to tickle the insect with a straw or to grip one of its
legs with the tweezers and the eighteen scent-bottles at once begin to
work. Whoso handles the grub will find his fingers stink and will throw
away the noisome perfumer in disgust. If the Chrysomela-larva’s object
in placing nine pairs of nitrobenzene-stills on its back was to repel
man, it has, I admit, thoroughly succeeded.
But man is the least of its enemies. Far more formidable is the
Odynerus, who seizes the scented creature by the skin of the neck and,
despite its sprays of perfume, dispatches it with a few stings. This
was the bandit against whom, above all, it should have defended itself;
and the poor grub has not been happily inspired in this respect.
Considering the huntress’ exclusive taste for this sort of game, we
must presume that the Chrysomela’s drug-shop possesses a delicious
aroma in the Odynerus’ opinion. The defensive secretion becomes a
deadly bait. Even so with other means of protection: each advantage
invariably has some corresponding disadvantage.
I have read, I forget where, the story of certain South-American
Butterflies, some of whom tasted bitter, others not. The first were
respected by the birds because of their bitterness; the second were
eagerly swallowed. What did the persecuted insects do? Unable to
acquire the disagreeable flavour of the bitter ones, they at least
imitated their shape and their costume. And the birds were taken in by
the fraud.
This was put forward as a striking proof of evolution in view of the
struggle for life. I am repeating the story more or less correctly, as
it lingers vaguely in my memory, for I have never attached more
importance than they deserve to pretty inventions of this kind. Is it
really certain that the pungent Butterflies escaped destruction because
of their taste? Might there not be, among the birds, a few passionate
lovers of bitters, to whom the defensive flavour was, on the contrary,
an added lure? My two acres of pebbles tell me nothing of things
Brazilian; nevertheless I learn within their four walls that a grub of
detestable flavour, of the most repulsive aroma, has, like the others,
its appointed consumers and very zealous consumers at that. If the
struggle for life made it acquire its scent-bottles, then the struggle
for life is a fool: it should have left the creature without them. In
this way the enemy most to be feared, the Odynerus, who is attracted by
the smell, would have been avoided.
The non-pungent Butterflies teach us something more. In order to
protect themselves from the birds, they have imitated the pungent ones’
costume. Pray, then, let some one tell us why, among so many naked
larvæ on which the little birds feast, not one has thought of assuming
the Chrysomela’s black-buttoned overall. Unable to provide themselves
with stinking retorts, they should at least possess a colourable
imitation, in order to put their persecutors off. The simple creatures!
It never entered their heads to protect themselves by mimesis! We will
not blame them; it is not their fault. They are what they are; and no
bird’s beak will make them change their costume.
The Chrysomela’s defensive fluid has a look of essential oil: it
discolours paper with a semitransparent stain which disappears by
evaporation. Its colour is opalescent; its flavour is horrible; its
odour is excessively strong and may be compared with that of the
nitrobenzene of our laboratories. Were it not that I lack the leisure
and the apparatus, I would gladly undertake a little research-work into
this singular product of animal chemistry, which, I think, is quite as
worthy of exploration by our tests as the milky exudations of the
Salamander or the Toad. Meanwhile I commend the problem to the
chemists.
In addition to the eighteen flasks of essential oil, the grub possesses
yet another protective device, which is at once defensive and
locomotory. The end of the intestine expands, at the insect’s pleasure,
into a large amber-coloured pimple, whence oozes a colourless or very
pale-yellow liquid. I find it difficult to distinguish the odour of
this liquid, because the strip of paper on which I collect it is always
infected by the creature’s mere touch. Nevertheless I seem to
recognize, in a fainter degree, the smell of nitrobenzene. Can there be
any connection between the product of the dorsal flask and that of the
intestinal pimple? There very well may be. I suspect, also, that it
possesses special virtues, for the Odynerus, who is a fine judge in
such matters, will tell us presently how greatly she appreciates this
liquid.
Before taking the evidence of the huntress, let us note that the grub
employs its anal pimple to move along with. Too short in the legs, it
is a sort of cripple using its inflated stern as a lever. Another fact,
whose interest will appear at the proper time, is that, at the moment
of the metamorphosis, the larva fastens itself by the anus to a
poplar-leaf. The larval skin is pushed back while it remains clinging;
and the nymph appears half-sheathed in this slough. The nymph in its
turn splits; the perfect insect releases itself; and the two cast-off
suits of clothes, one partly enclosed within the other, retain their
place on the leaf, fastened to it by the anal extremity. The nymphosis
takes about twelve days in all. It would be irrelevant to linger any
longer over the larva of the Chrysomela; the little which it is
expedient to say must not exceed the limits of my subject, which is the
story of the Odynerus.
We know the game grazing on its poplar-leaf in the sun; let us see it
stowed away in the larder. I count the number of head in a reed-stump
occupied by seventeen cells, with their stores of food complete, or
nearly so, some still containing the egg, the others a young larva
attacking its first morsel. In the best-provisioned cells ten grubs are
packed together; in those least well-supplied there are only three. I
perceive, moreover, that, generally speaking, the abundance of
provisions diminishes in the upper and increases in the lower stories,
though the order of progression is not always very exact. The varying
ration of the two sexes is probably responsible: the males, which are
smaller and more forward, are given the upper chambers, with a frugal
bill of fare; the females, which are larger and more backward, are
given the lower chambers, with a plentiful table. Another reason, I
think, contributes to these variations in number, namely, the size of
the game, which is more or less young, more or less plump.
Whether big or small, all the head of game are absolutely motionless.
Armed with a magnifying-glass, I watch in vain for any oscillation of
the palpi, any quivering of the tarsi, any pulsation of the abdomen,
symptoms of life so frequently observed in the victims of the predatory
Wasps. There is nothing, ever. Can the larvæ stabbed by the Odynerus be
really dead? Can the provisions consist of actual corpses? By no means:
their profound inertia does not preclude a remnant of life. The proofs
are striking.
To begin with, inspected cell by cell, my bundle of reeds tells me that
the big larvæ, those which have acquired their full development, very
often adhere by their hinder part to the walls of the cell. The meaning
of this detail is evident. Captured when the metamorphosis was at hand,
the grub, despite the blows of the stiletto, has made its usual
preparations: it has hung itself firmly to the adjoining support, the
earthen partition or the tube of the reed, just as it fastens itself to
the poplar-leaf. The creature is so fresh in appearance and its anal
adhesion is so accurate that I actually hope to see the victim’s skin
split and the nymph appear. My hope is not at all exaggerated; it is
based on facts no less curious which I shall describe later. Events did
not respond to the probabilities on which I all but relied. When
removed from the charnel-house with their point of support and put in a
safe place, none of the larvæ settled for the nymphosis went beyond the
preparatory action. This action in itself, however, is eloquent enough:
it tells us that a remnant of life faintly animates the grub, since it
retains power to make the necessary arrangements for the
transformation.
That the grub is no corpse is revealed in another manner. I place in
glass tubes, with a plug of cotton, twelve larvæ removed from the
Odynerus’ larders. The sign of latent life is the creature’s freshness
and its hue, a soft pinky white; the sign of death and corruption is a
brown colouring. Well, eighteen days later one of the grubs begins to
turn brown. A second is seen to be dead in thirty-one days. In
forty-four days, six are still fresh and full. Finally, the last
continues in good condition for two months, from the 16th of June to
the 15th of August. It goes without saying that, under the same
conditions, larvæ which are really dead and unbruised, larvæ
asphyxiated with bisulphide of carbon, turn brown in a few days.
As I should have expected, the laying-peculiarities of the
Nest-building Odynerus are precisely identical with those of O.
reniformis, the object of my earlier observations. I again witness,
with the satisfaction that results from verifying an interesting fact,
the curious arrangements already described. The egg is laid first,
right at the back of the cell. Next comes the stacking of the
provisions in the order of capture. In this way the eating proceeds
from the oldest to the most recent.
I was above all anxious to ascertain whether the egg was pendulous,
that is to say, whether it hung by a thread at one point of the cell,
in accordance with what I had learnt from the Eumenes and from O.
reniformis. A kinswoman of the latter must, I felt certain beforehand,
conform to the method of the suspension-cord; but there was reason to
fear that the journey from Orange and the jolting of the cart might
have broken the delicate pendulum. I recalled my anxieties, my minute
precautions, during the removal of the cells with the egg of O.
reniformis swinging from the ceiling. The cart, ignorant of its
precious burden, might have undone everything.
But no, to my great surprise. In most of the cells which were
sufficiently recent I find the egg in place, slung sometimes from the
arched roof of the reed, sometimes from the upper edge of the
partition, by a thread which is just visible and about one twenty-fifth
of an inch long. The egg is itself cylindrical and measures about an
eighth of an inch. The reeds, opened wide and placed in glass tubes,
enable me to witness the hatching, which takes place three days after
the closing of the cell and probably four days after the laying.
I see the new-born grub enclosed almost wholly, head downwards, in the
sheath provided by the pellicle of the egg. Very slowly it slides
forward in this scabbard and the suspension-cord stretches to the same
extent. It is extremely fine in the part consisting of the original
thread, but very much thicker in the portion resulting from the slough
of the egg. The grub’s head reaches the nearest piece of game at one
point or another; and the fragile creature takes its first mouthful. If
anything startles it, if I tap the reed, it lets go and withdraws a
little way into the sheath of the egg; then, reassured, it once more
glides forward and resumes the point attacked. At other times a jerk
leaves it indifferent. This suspension-stage of the new-born larva
continues for about twenty-four hours, after which the grub, now
somewhat fortified, lets itself drop and eats in the ordinary manner.
The victuals last it for twelve days. Immediately afterwards comes the
working of the cocoon, in which the insect remains, a yellow larva,
until next May. It would be tedious to follow the Odynerus in its
career of eating and weaving. The consumption of dishes highly spiced
with nitrobenzene and the spinning of the cocoon, of a fine
amber-coloured fabric, involve nothing so remarkable as to deserve
special mention.
Before leaving this subject, I will state a problem which the pendulous
egg sets to the embryogenist. Every insect’s egg, if cylindrical in
form, has two poles, the front and back, the cephalic and the anal
pole. By which of the two does the insect see the light?
By the hinder pole, the Eumenes and the Odyneri tell us. The end of the
egg fastened to the wall of the cell was evidently the first to issue
from the oviduct, in view of the mother’s absolute need first to glue
the suspension-thread somewhere, before abandoning her egg to space. In
the ovarian tubes and in the oviduct, which are too narrow to allow of
an inversion, the anal pole therefore passes first. Pointing in the
same direction as the egg, the new-born grub will thus hang head
downwards, with its hinder end uppermost, at the end of its thread.
By the front pole, the Scoliæ, the Spheges and the Ammophilæ in their
turn reply, as do all the Hunting Wasps that fix the egg to some
portion of the victim. It is, indeed, always by the cephalic end that
the egg adheres to the prey, at a definite point selected by the
mother’s prudence; for the safety of the nurseling and the preservation
of the victuals demand that the first bites shall be taken here and
here only. For the same reasons as above, the extremity fastened to the
game has emerged into the light of day before the other.
Both these opposite testimonies are equally truthful. According as its
destiny is to be glued to the wall of the cell or to be kept away from
it on another support, the egg takes its plunge into life by the front
pole or the rear pole, which requires an inverse direction in the
ovaries and the oviduct. In this manner the new-born grub always has
its food under its mandibles; and its utter lack of experience does not
expose it to the danger of death from inanition in front of a heap of
provisions which its mouth would not yet be able to seek and find.
There is the problem. I beg and entreat the embryogenists to solve it,
without reference to preordination, with the sole aid of protoplastic
energy.
To know the Odynerus in the privacy of her home was not enough: the
thing was to see her also at work as a huntress. How does she capture
her game? How does she operate on it, in order to keep it fresh while
deprived of life and movement? What is her surgical method? As, for the
moment, I knew of no smallest colony of the Chrysomela’s persecutor in
my neighborhood, I put the matter to Claire. She was on the spot, in
daily contact with the Hen-house where the memorable events that form
the subject of this essay occurred; and—a most important circumstance—I
knew her to be both quick-witted and willing. She accepted the
burdensome task with enthusiasm. I, on my side, was, if possible, to
attempt certain observations with the captive insect. So as not to
influence each other in our appreciation of facts which, by their
rapidity, might leave room for doubt, we each agreed to keep our
results secret until we were both certain of our data.
Fully instructed as to what to do, Claire begins. She soon discovers on
the banks of the Aygues some poplars covered with Chrysomela-larvæ.
From time to time an Odynerus arrives, alights upon a leaf and goes off
again with her capture in her legs. But things are happening too high
up; detailed inspection of the struggle between the huntress and the
victim is impracticable. Moreover, the appearances of the Odynerus on
the tree which was being watched among so many others, all equally
propitious to the chase, occur at long intervals, which try the
patience beyond all bounds. Tenacious in her desire to see, to learn
and to be useful to me, my zealous collaborator bethinks herself of an
ingenious expedient. A young poplar, with a wealth of Chrysomelæ, is
pulled up, together with the lump of earth clinging to it. Lavish
precautions are taken to avoid the shocks which, during the uprooting
and the removal, might cause the herd of larvæ to drop off. The
business is so successfully done that the tree arrives without a hitch
at its destination, in front of the Hen-house. It is put back in the
earth immediately facing the reeds wherein the Odynerus makes her
dwelling. No matter whether it takes root again or not, provided that
the little tree keep fresh for a few days with abundant watering: that
is all that is wanted.
After installing her observatory, Claire proceeds to lie in wait,
hiding behind some branches beside the poplar, whose foliage is in full
view. She watches in the morning; she watches when the heat of the day
has come; she watches in the afternoon. Next day, she begins again; on
the day after that, she is still at it; and so she continues until at
last fortune smiles upon her. O blessed patience, of what are you not
capable! The swarm of Odyneri, out in search of larvæ, were, on their
return, warned by the smell of nitrobenzene of the presence of the
transplanted and game-laden poplar. Why make distant expeditions when
the quarry abounds outside one’s door? The little tree was extensively
exploited. Under such conditions the huntress was not long in revealing
the secret of her tactics. Over and over again Claire witnessed the act
of murder by the dagger. But she paid dearly for satisfying our common
curiosity; she had to keep her room for several days as a result of
sunstroke. For that matter, she was prepared for the misadventure, well
knowing, from my own example, that this is the assured reward of
observations made beneath an implacable sun. May the eulogies of
science repay her for a little headache! The results of her watches
agreed at all points with those of my own. I shall explain them by
telling what I saw myself.
Now for my turn. When the bundle of reeds selected by the Odyneri
reached me, I was occupied with a most interesting question, as will be
proved by the details reserved for another chapter. [60] I was
endeavouring to make the various Hunting Wasps, the species of whose
prey was known to me, operate under a wire cover in my insect
laboratory. This would determine the precise spots into which the sting
was driven. My captives, confronted with their ordinary game, for the
most part refused to unsheathe their weapons; others, less intent upon
outdoor hunting, accepted the offer and stabbed their victims under my
magnifying-glass. Why should not the Nest-building Odynerus be among
these bold ones?
We will try. I have plenty of Chrysomela-grubs, received from Orange; I
keep them under a wire-gauze dome, with an eye to their metamorphoses
and their perfume-stills. The game is at hand; the huntress is lacking.
Where shall I catch her? I have only to ask Claire, who will hasten to
send her. This is a sure expedient, but I hesitate to employ it: I fear
lest the insect should reach me demoralized by the jolting of the cart
and the tedium of a long captivity. To this bored and wearied creature
an encounter with the Chrysomela will almost surely be a matter of
indifference. I must have something better: I want the insect captured
that moment with its aptitudes in their prime.
In front of my door is a field of yellow fennel-flower, an ingredient
of that ill-famed liquor, absinthe. From its umbels Wasps, Bees and
Flies of all sorts drink their fill. Let us take the net and see. The
banqueters are numerous. I inspect the rows of plants amid the
drinking-songs, the buzzing and the shrilling of the insects. Praise
the Lord, here is the Odynerus! I catch one, I catch two, I catch six
of them and I hurry back to my workroom. Fate is favouring me beyond my
desires: my six captures belong to the Nest-building Odynerus and all
the six are females. Any one passionately interested in a problem and
suddenly discovering the data required for its solution will understand
my emotion. The joy of the moment has its anxious side: who knows what
turn things will take between the huntress and the quarry? I shift an
Odynerus and a Chrysomela-larva into a bell-glass. To stimulate the
assassin’s ardour, I set the glass cage in the sun. Here is the story
of the drama, told in detail.
For a good quarter of an hour, the captive clambers up the sides of the
bell-glass, crawls down again and up again, seeking an outlet whereby
to escape, and seems to pay no attention to the game. I was already
despairing of success when suddenly the huntress falls upon the larva,
turns it over, belly upwards, clasps it and stings it thrice in
succession in the thorax, particularly under the neck, in the median
region, a point at which the sting is more insistent than elsewhere.
The close-clasped larva does its utmost to protest, emptying its
scent-bottles and oiling itself with petrol; but these defensive
tactics have no effect. Indifferent to the heady perfume, the Odynerus
performs her operation, wielding her lancet with the same certainty as
if the patient were scentless. Thrice the sting is driven in, to kill
the motor nerves in the three ganglia of the thorax. I repeat the
experiment with other subjects. Few refuse to attack the prey; and each
time three stings are administered with marked insistence at the point
under the neck. What I saw under artificial conditions Claire, on her
side, saw under conditions of liberty, in the open air, on the leaves
of the transplanted poplar. The two collaborators, she and I, arrived
at precisely the same result.
The operation is rapidly performed. Then the Odynerus, while dragging
her prey along, belly to belly, munches at its neck for a considerable
time, but without causing any wound. This action may well be equivalent
to the practice of the Languedocian Sphex and the Hairy Ammophila, [61]
when, without inflicting a bruise, the one nibbles at the neck of her
Ephippiger and the other at that of her Grey Worm, in order to compress
and paralyse the cervical ganglia. I of course take possession of the
torpid larvæ. The victim is absolutely inert, save for a slight
quivering of the legs, which soon ceases. When laid upon its back, the
larva no longer stirs. It is not dead, however; that I have been able
to prove. Its dull vitality is affirmed in another manner. During the
first few days of this lethargy which knows no awakening, droppings are
ejected until the intestine is empty.
On renewing my experiments, I witness something so singular that I am
at first baffled. This time the prey is seized by the anal extremity
and the sting is driven several times into the last segments,
underneath the abdomen. This is the usual operation reversed and
performed upon the hinder segments, instead of those of the thorax. The
surgeon and the patient, who are head to head in the normal method, are
in the present instance head to tail. Can it be by inadvertence that
the operator is confusing the two ends of the grub and stinging the tip
of the abdomen under the impression that she is stinging the neck? I
believe it for a moment, but am soon undeceived. Instinct does not make
mistakes of this sort.
For now, having finished thrusting with her sting, the Odynerus clasps
the creature and begins slowly, with great bites of the mandibles, to
munch the last three segments, on the dorsal surface. A manifest
gluttony accompanies these bites; all the mouth-parts are brought into
play, as though the insect were feasting on some exquisite dish.
Meanwhile the grub, bitten to the quick, desperately works its short
legs, whose activity is not at all diminished by the stings
administered behind; it struggles violently, protesting with its head
and mandibles. The other takes no notice and continues gnawing at the
larva’s rump. This lasts for ten or fifteen minutes; then the bandit
releases the sufferer and leaves it where it lies, without troubling
about it any further, instead of carrying it with her as she would not
fail to carry game intended for the nest. Soon afterwards, the Odynerus
begins to lick her fingers, as though she had been consuming some
toothsome dainty: time after time she passes her tarsi between her
mandibles; she is washing her hands after rising from table. What has
she been eating? I must once more watch the epicure squeeze the juice
from the rump.
Ever obliging, provided that I practise a little patience, my six
captives, one after the other, operate on the Chrysomela-larvæ, at one
time in front, as game for the family, at another behind, as a little
addition to their own diet. The honey with which I serve them on spikes
of lavender does not make them forget this horrible treat. The tactics
employed in obtaining it, though the same in the general aspect, vary
in detail. The larva is always seized by the hinder end and the stings
are administered in succession from back to front, on the ventral
surface. Sometimes the abdomen only is attacked, sometimes the thorax
also, when the victim is deprived of all movement. Evidently the object
of these stings is not the immobility of the larva, since the latter
can move quite well, ambling along, wounded though it be, when the
sting has not gone higher than the abdomen. Inertia is indispensable
only in the case of victuals intended for the cells. If the Odynerus is
working on her own behalf and not for her family, it matters little to
her whether the grubs whose dainties she covets struggle or not; it is
enough if all resistance in the part to be exploited is abolished by
paralysis. This paralysis, moreover, is quite accessory; and each
huntress neglects or practises it at will, bearing more or less
forward, without any fixed rule. When the sated Odynerus releases the
grub whose rump she has been chewing, it is sometimes therefore inert,
like those intended for the cells, and sometimes endowed with almost as
much activity as the untouched grubs, from which it differs only by the
absence of its anal pimple, its support which reminds us of a cripple
sitting in a bowl.
I examine the helpless ones. The anal blister has disappeared, nor can
I make it reappear by squeezing the tip of the abdomen with my fingers.
For the rest, in the place of this blister my pocket-lens shows me
torn, rugged tissues; the end of the intestine is in tatters. Every
elsewhere all around are bruises and contusions, but no gaping wounds.
It is with the contents of the blister then that the Odynerus so
deliciously slakes her thirst. When she munches the last two or three
segments, she is milking the grub after a fashion; by means of the
pressure, which favours the paralysis of the abdomen, she makes the
rectal humour flow into the pocket, which she then rips open in order
to sip the contents.
What is this humour? Some special product, some mixture of
nitrobenzene? I cannot say for certain. I know only that the insect
employs it in self-defence. When frightened, it exudes it to ward off
the assailant. The anal reservoir begins to work when the first little
drop appears from the scent-bottles. What shall we say of this
protective device which becomes the cause of excruciating torture?
Unsophisticated creatures, acquire the power of stinking, after this;
distil benzene; become bitter if you were not bitter before: you will
always find a devourer to scrunch you, an epicure to nibble your rump!
South-American butterflies, pray take note!
I will not close the lamentable history of the Chrysomela-grub without
telling what becomes of the creature after this horrible mutilation.
The complete inertia produced by the thoracic injuries has nothing to
teach us that we do not already know from the facts perceived in the
larvæ destined for the cells. We will therefore consider the case in
which the grub is stung three or four times at the tip of the abdomen
only. I secure the creature when the Odynerus abandons it, after
greedily munching the last three segments and scraping out the end of
the intestine, whose defensive and locomotory pimple has disappeared.
These three segments are bruised and of a sickly colour; but I cannot
discover the least rent in the skin. The abdomen is paralysed. The
insect no longer uses its anal lever when walking. The legs are
perfectly mobile and the grub employs them: it crawls, it drags itself
along, progressing with a vigour which would be normal but for the
obstruction of the hind-quarters. The head also moves; the mouth-parts
snap as usual. Apart from the paralysis of the abdomen and the
mutilation of the rectum, the victim is in every respect the same as
the lusty larva, browsing peacefully on the poplar-leaf. We have here a
magnificent demonstration of the principle before which certain peevish
objections are bound to fall to the ground: the effect of the sting is
not felt, at least not at first, except at the points attacked. The
sting strikes the nerve-centres of the abdomen and the abdomen is
paralysed; it spares the thorax and the legs and head both remain
active.
Ten hours after the operation, I examine the grubs again. The hind-legs
are tremulous and are no longer of use for locomotion. Paralysis is
overtaking them. Next day, they are inert; so are the middle legs. The
head and the fore-legs are still working. On the day after, the whole
grub is motionless, except the head. Lastly, on the fourth day, the
creature is dead, really dead, for it shrivels, dries up and goes
black, while the larvæ subjected to the thoracic operation with a view
to being used for provisions remain full and fresh-coloured for weeks
and months. Did the grub die of its stings in the abdomen? No, for the
others, stung in the thorax, do not die. It is the Odynerus’ cruel
tooth and not the sting that killed it. With the tip of the abdomen
crushed under the mandibles and the intestinal capsule pulled out by
the roots, life has ceased to be possible.