THE ODYNERI
The Eumenes’ suspension-cord and ascending-sheath are rendered
necessary by the large number and the incomplete paralysis of the
caterpillars provided for the larva; the object of the ingenious system
is to avert danger. This, at least, is how I regard the concatenation
of causes and effects. But I yield to no one in my distrust of whys and
wherefores; I know how slippery our footing becomes when we venture on
interpretations; and, before declaring the reasons of any fact
observed, I seek for a batch of proofs. If the singular installation of
the Eumenes’ egg is really due to the reasons suggested, then, wherever
we find similar conditions of danger, namely, a multiplicity of dishes
combined with incomplete torpor, we must also find a similar method of
protection, or some other method having an equivalent effect. The
repetition of the act will bear witness to the correctness of the
interpretation; and, if it is not reproduced elsewhere, with such
variations as may be required, the case of the Eumenes will remain a
very curious instance, without acquiring the far-reaching significance
which I suspect it of bearing. Let us generalize, the better to
establish the facts.
Now not far removed from the Eumenes are the Odyneri, the Solitary
Wasps observed by Réaumur. [14] They have the same costumes, the same
wings folded lengthwise, the same predatory instincts and, above all,
as the supreme condition, the same accumulations of prey retaining
sufficient power of movement to be dangerous. If my arguments are
well-founded, if I am right in my conjectures, the egg of the Odynerus
should be slung from the ceiling of the cell like the egg of the
Eumenes. My conviction, based upon logic, is so positive that I already
seem to see this egg, recently laid, quivering at the end of the
life-line.
Ah, I confess that it needed a robust faith to cherish the audacious
hope of discovering anything further when the masters had seen nothing!
I read and reread Réaumur’s essay on the Solitary Wasp. The Insect’s
Herodotus gives us a host of particulars, but says nothing, absolutely
nothing, about the hanging egg. I consult Léon Dufour, [15] who treats
subjects of this kind with his usual raciness: he has seen the egg; he
describes it; but of the suspension-thread not a word. I consult
Lepeletier, [16] Audouin, [17] Blanchard: [18] they are absolutely
silent on the means of protection which I expect to find. Is it
possible that a detail of such great importance can have escaped all
these observers? Am I the dupe of my imagination? Is the protective
system, though proved to my mind by close logical reasoning, merely one
of my dreams? Either the Eumenes have lied to me or my hopes are
justified. As a disciple rebelling against his masters, a disciple
strong in arguments which I believed invincible, I set to work
investigating, convinced that I should succeed. And I did succeed; I
found what I was looking for; I found something better still. Let me
set things down in detail.
There are various Odyneri established in my neighbourhood. I know one
who takes possession of the abandoned nests of Eumenes Amadei. This
nest, a structure of unusual solidity, is not a ruin when its owner
moves away; it loses only its neck. The cupola, preserved untouched, is
a fortified retreat of too convenient a nature to remain vacant. Some
Spider adopts the cavern, after lining it with silk; Osmiæ [19] take
refuge in it in rainy weather, or else make it their dormitory, wherein
to spend the night; an Odynerus divides it, by means of clay
partitions, into three or four chambers, which become the cradles of as
many larvæ. A second species uses the deserted nests of the Pelopæus;
[20] a third, removing the pith from a dry bramble-stem, obtains, for
the use of her family, a long sheath, which she subdivides into
stories; a fourth bores a gallery in the dead wood of some fig-tree; a
fifth digs herself a shaft in the soil of a footpath and surmounts it
with a cylindrical, vertical kerb. All these industries are worth
studying, but I should have preferred to discover that which Réaumur
and Dufour have rendered famous.
On a steep bank of red clay, I at length recognize, in no great
profusion, the signs of a village of Odyneri. Here are the
characteristic chimneys mentioned by the two historians, that is to
say, the curved tubes, with their guilloche-work, that hang at the
entrance to the dwelling. The bank is exposed to the heat of the
noonday sun. A little tumbledown wall surmounts it; behind is a dense
screen of pines. The whole forms a warm refuge, such as the Wasp
requires for setting up house. Moreover, we are now in the second
fortnight of the month of May, which is just the working-season,
according to the masters. The outside architecture, the site and the
period all agree with what Réaumur and Léon Dufour have told us. Have I
really chanced upon one or other of their Odyneri? This remains to be
seen and without delay. Not one of the ingenious constructors of
guilloche porticoes shows herself, not one arrives; I must wait. I take
up my position close by, to watch the homing insects.
Ah, how long the hours seem, spent motionless, under a burning sun, at
the foot of a declivity which sends the heat of an oven beating down
upon you! Bull, my inseparable companion, has retired some distance
into the shade, under a clump of evergreen oaks. He has found a layer
of sand whose depths still retain some traces of the last shower. He
digs himself a bed; and in the cool furrow the sybarite stretches
himself flat upon his belly. Lolling his tongue and thrashing the
boughs with his tail, he keeps his soft, deep gaze fixed upon me:
“What are you doing over there, you booby, baking in the heat? Come
here, under the foliage; see how comfortable I am!”
That is what I seem to read in my companion’s eyes.
“Oh, my Dog, my friend,” I should answer, if you could only understand,
“man is tormented by a desire for knowledge, whereas your torments are
confined to a desire for bones and, from time to time, a desire for
your sweetheart! This, notwithstanding our devoted friendship, creates
a certain difference between us, even though people nowadays say that
we are more or less related, almost cousins. I feel the need to know
things and am content to bake in the heat; you feel no such need and
retire into the cool shade.”
Yes, the hours drag when you lie waiting for an insect that does not
come. In the pinewood hard by, a couple of Hoopoes are chasing each
other with the amorous provocations of spring:
“Oopoopoo!” cries the cock, in a muffled tone. “Oopoopoo!”
Latin antiquity called the Hoopoe Upupa; Greek antiquity named it Ἔποψ.
But Pliny turned the ἔ into ou and must have pronounced the word
Oupoupa, as the cry imitated by the name teaches me to do. Rarely have
I received a lesson in Latin pronunciation better authenticated than
yours, [21] you beautiful bird, who provide a diversion for my long
hours of weariness. Faithful to your idiom, you say “Oopoopoo!” as you
said in the days of Aristotle and Pliny, as you said when your note
sounded for the first time. But our own idioms, our primitive idioms,
what has become of them? The scholar cannot even recover their traces.
Man alters; animals do not change.
At last, here we are at last! See, the Odynerus arrives, with a flight
as silent as the Eumenes’. She disappears into the curved cylinder of
the vestibule, bringing home a grub beneath her abdomen. I place a
small glass test-tube at the entrance to the nest. When the insect
emerges, it will be caught. Done! The Wasp is caught and at once
decanted into the asphyxiating-flask, with its strips of paper steeped
in bisulphide of carbon. And now, my Dog, still lolling your tongue and
frisking your tail, we can be off; the day has not been wasted. We will
come back to-morrow.
Upon investigation, my Odynerus does not correspond with what I
expected to see. This is not the species of which Réaumur speaks (O.
spinipes); nor is it the species studied by Dufour (O. Reaumurii); it
is another. (O. reniformis, Latr.), a different one, though addicted to
the same arts. Already the naturalist of the Landes had allowed himself
to be deceived by that similarity in architecture, provisions and
habits; he thought that he was observing Réaumur’s Solitary Wasp,
whereas in reality his tube-builder presented specific differences.
We know the worker; it remains for us to become acquainted with her
work. The entrance to the nest opens in the perpendicular wall of the
bank. It is a round hole, on the edge of which is built a curved tube,
with the orifice turned downwards. Made with the materials cleared from
the burrow under construction, this tubular vestibule is composed of
grains of earth, not arranged in continuous courses, but leaving small
vacant intervals. It is a species of open-work, a lacework of clay. Its
length is about an inch and its internal diameter a fifth of an inch.
This portico is continued by the gallery, of the same diameter, which
slants into the soil to a depth of nearly six inches. Here this main
gallery branches into short corridors, each giving access to a cell
which is independent of its neighbours. Each larva has its chamber,
which can be reached by a special passage. I have counted as many as
ten of them; and there may be more. These chambers have nothing
remarkable about them, either in construction or in capacity; they are
just culs-de-sac ending the corridors that give access to them. Some
are horizontal, some more or less sloping; there is no fixed rule. When
a cell contains what it is meant to contain, the egg and the
provisions, the Odynerus closes the entrance with a little earthen lid;
she then digs another near it, on one side of the principal gallery.
Lastly, the common road to the cells is blocked with earth; the tube at
the entrance is demolished, to furnish material for the work done
inside the nest; and every vestige of the habitation disappears.
The surface of the bank is of clay baked in the sun; it is almost
brick. I break into it with difficulty, making use of a small
pocket-trowel. Underneath, it is much less hard.
How does the frail miner manage to sink a gallery in this brick? She
employs, I cannot doubt, the method described by Réaumur. I will
therefore reproduce a passage from the master’s writings, to give my
younger readers a glimpse into the habits of the Odyneri, habits which
my very small colony did not enable me to observe in all their details:
“It is at the end of May that these Wasps set to work; and one can
see them busily labouring during the whole of June. Though their
actual object is only to dig in the sand a hole a few inches deep
and not much wider than their bodies, one might suppose that they
had another end in view; for, to make this hole, they build on the
outside a hollow tube, which has as its base the circumference of
the entrance to the hole and which, after following a direction
perpendicular to the surface containing that aperture, turns
downwards. This tube becomes longer in proportion as the hole
becomes deeper; it is built of the sand drawn from the hole; it is
fashioned in coarse filigree, or a sort of guilloche. It is made of
big, granular, winding fillets, which do not touch at all points.
The gaps left in between make it look as if it were artistically
constructed, whereas it is only a sort of scaffolding by means of
which the mother’s tactics are rendered swifter and surer.
“Though I knew these insects’ two teeth to be capital instruments,
capable of breaking into very hard substances, the task which they
had to perform appeared to me rather severe for them. The sand on
which they had to act was scarcely less hard than ordinary stone;
at least, one’s finger-nails made but a poor impression upon its
outer layer, which the sun’s rays had dried more thoroughly than
the rest. But, when I succeeded in observing these workers at the
moment when they were beginning to bore a hole, they taught me that
they did not need to subject their teeth to so harsh an ordeal.
“I saw that the Wasp begins by softening the sand which she
proposes to remove. Her mouth discharges upon it a drop or two of
water, which is promptly swallowed by the sand, turning it
instantly into a soft paste which her teeth scrape and remove
without difficulty. Two of her legs, the foremost pair, immediately
proceed to gather it into a little pellet, about the size of a
currant-seed. It is with this pellet, the first one removed, that
the Wasp lays the foundations of the tube which we have described.
She carries her pellet of mortar to the edge of the hole which she
has just made by removing it; her teeth and feet turn it about,
flatten it and make it stand up higher than it did before. This
done, the Wasp again sets about removing sand and loads herself
with another pellet of mortar. Soon she contrives to have extracted
enough sand to make the entrance of the hole perceptible and to
have laid the foundation of the tube.
“But the work can proceed quickly only so long as the Wasp is able
to moisten the sand. She is obliged to take trouble to renew her
store of water. I do not know whether she simply went to take in
water at some stream, or whether she drew, from some plant or
fruit, a more sticky fluid; what I do know is that she returned
without delay and set to work with renewed zeal. I observed one
Wasp who managed, in about an hour, to sink a hole the length of
her body and who raised a chimney as tall as the hole was deep. At
the end of a few hours the tube stood two inches high and she was
still deepening the hole that lay underneath.
“It did not appear to me that she had any rule respecting the depth
which she gives it. I have found some whose hole ran more than four
inches from the orifice; others whose hole measured only two or
three inches. Again, over one hole you will find a tube twice or
three times as long as that over another. Not all the mortar
removed from the hole is invariably employed to prolong it. In
cases where the Wasp has given the tube a length which she
considers sufficient, you see her simply arrive at the opening to
the tube, put her head beyond its edge and forthwith drop her
pellet, which falls to the ground. In this way I have often
observed a quantity of rubbish at the foot of certain holes.
“The object for which the hole is pierced in a solid mass of mortar
or sand cannot appear in doubt: it is plainly intended to receive
an egg, together with a store of foodstuffs. But we do not so
easily see to what end the mother has built the mortar shaft. By
continuing to follow her labours, we shall discover that it means
to her what a stack of well-laid stones means to the masons
building a wall. Not the whole of the tunnel which she has
excavated is intended as a lodging for the larva which will be born
inside; a portion will be quite enough. Yet it was necessary that
the hole should be dug to a certain depth, in order that the larva
may not find itself exposed to too great a heat when the sun’s rays
fall on the outer layer of sand. It will occupy only the end of the
tunnel. The mother knows what space she must leave vacant and this
space she retains; but she fills up all the remainder and replaces
in the upper portion of the hole as much of the sand removed from
it as is necessary to stop it up. It is to have this mortar within
reach that she has built that shaft. Once the egg is laid and the
store of victuals placed within its reach, we see the mother come
and gnaw the end of the shaft, after first moistening it, carry the
pellet inside and next return for more, in the same manner, until
the hole is blocked right up to the opening.”
Réaumur goes on to speak of the victuals heaped up in the cells, the
“green grubs [22],” as he calls them, heedless of the ugly
alliteration. Not having seen the same things, because my Odynerus is
of a different species, I will continue my story. I counted the head of
game in three cells only: the colony was a small one; I had to deal
tenderly with it if I would follow its history to the end. In one of
the cells, before the provisions were broached, I counted twenty-four
pieces; in each of the two others, which were likewise intact, I
counted twenty-two. Réaumur found only eight to twelve pieces in the
larder of his Odynerus; and Dufour, in the store-room of his,
discovered a batch of ten to twelve. Mine requires twice as many, a
couple of dozen, which may be due to the smaller size of the game. No
predatory Wasp of my acquaintance, apart from the Bembeces, [23] who
obtain their supplies from day to day, approaches this prodigality in
numbers. Two dozen grub-worms to make a meal for only one! How far
removed are we from the single caterpillar of the Hairy Ammophila! And
what delicate precautions must be taken for the safety of the egg in
the midst of such a crowd! A scrupulous vigilance is necessary here, if
we would obtain a true conception of the dangers to which the Odynerus’
egg is exposed and of the means that save it from danger.
And, in the first place, what variety of game is this? It consists of
worms as thick as a knitting-needle and varying slightly in length. The
biggest measure a centimetre. [24] The head is small, of an intense,
glossy black. The segments, unlike those of the caterpillars, have no
legs, either true or false, but all, without exception, are furnished
with ambulatory organs in the shape of a pair of small fleshy nipples.
These worms, though of the same species, to judge by their general
characteristics, differ in colouring. They are a pale, yellowish green,
with two wide longitudinal stripes of pale pink in some and of a more
or less deep green in others. Between these two stripes, on the back,
runs a streak of pale yellow. The whole body is sprinkled with little
black tubercles, each bearing a hair on its crest. The absence of legs
proves that they are not caterpillars, not the larvæ of Butterflies or
Moths. According to Audouin’s experiments, Réaumur’s “green grubs” are
the larvæ of a Weevil, Phytonomus variabilis, an inhabitant of the
lucerne-fields. Can my worms, pink or green, also belong to some little
Weevil? It is quite possible.
Réaumur described the grubs composing the victuals of his Odynerus as
alive; he tried to rear some, hoping to see a Fly or a Beetle appear
from them. Léon Dufour, on his side, called them live caterpillars. The
mobility of the game provided escaped neither of the two observers;
they had before their eyes grubs that moved about and gave full signs
of life.
What they saw I also see. My little larvæ frisk and fidget; curled at
first in the shape of a ring, they uncurl themselves and curl again, if
I do no more than slowly turn the small glass tube in which I have
imprisoned them. When touched with the point of a needle, they struggle
abruptly. Some succeed in shifting their position. While engaged in
rearing the Odynerus’ egg, I opened the cell lengthwise, so as to
reduce it to a semicylinder; in the little trench thus made, which was
kept horizontal, I placed a few head of game. Next day usually I found
that one of them had fallen out, a proof of movement, of a change of
position, even when nothing was disturbing its repose.
These larvæ, I am firmly convinced, have been wounded by the Odynerus’
sting, for she would not carry a rapier merely for show. Possessing a
weapon, she employs it. However, the wound is so slight that Réaumur
and Léon Dufour did not suspect its existence. To their mind the prey
was alive; to mine it is very nearly alive. In these conditions we can
see to what perils the Odynerus’ egg would be exposed but for
exquisitely prudent precautions. There they are, those restless grubs,
to the number of two dozen in one cell, side by side with the egg,
which a mere nothing is enough to endanger. By what means will this
very delicate germ escape the perils of the crowd?
As I foresaw by my process of reasoning, the egg is slung from the
ceiling of the cell. A very short thread fastens it to the top wall and
lets it hang free in space. The first time that I saw this egg,
quivering at the end of its thread at the least jerk and confirming by
its oscillations the correctness of my theoretical views, I experienced
one of those moments of inward joy which atone for much vexation and
weariness. I was to have many more such moments, as will be seen. If we
pursue our investigations in the insect world with loving patience and
a practised eye, we always find some marvel in store for us. The egg, I
was saying, swings from the ceiling, held by a very short and extremely
fine thread. The cell is sometimes horizontal, sometimes slanting. In
the first case, the egg hangs perpendicularly to the axis of the cell
and its lower end approaches to within a twelfth of an inch of the
opposite wall; in the second case, the vertical direction of the egg
forms a more or less acute angle with that axis.
I wished to follow the progress of this hanging egg at my leisure, with
the greater convenience of observation which is possible at home. With
the egg of Eumenes Amadei this was all but impracticable, because of
the cell, which could not be moved together with the block that most
often serves as its foundation. A house of this kind demands
observation on the spot. The Odynerus’ dwelling does not present the
same drawback. When a cell is laid bare and found to be in the
condition which I desire, I dig round it with the point of a knife
until I detach a cylinder of earth containing the cell, which is
reduced to an open trough, so as to conceal nothing of what is to
happen inside. The victuals are extracted piecemeal, with every care,
and decanted separately into a glass tube. I shall thus avoid the
accidents that might be occasioned by the swarming heap of grubs during
the inevitable shaking of the journey. The egg alone remains, swinging
in the empty enclosure. A large tube receives the cylinder of earth,
which is wedged in position with pads of cotton-wool. I place my booty
in a tin box and carry it in my hand in such a position that the egg
hangs vertically without striking against the walls of the cell.
Never have I effected a removal which called for such nice precautions.
An accidental movement might easily break the suspension-thread, which
is so delicate that it needs the magnifying-glass to distinguish it;
excessive oscillation might bruise the egg against the walls of the
cell: I had to beware of turning it into a sort of bell-clapper dashing
against its bronze prison. I walked, therefore, with the stiffness of
an automaton, all of one piece, with steps methodically calculated.
What a misfortune should some acquaintance appear and make me stop a
moment, for a chat or a shake of the hand: the least distraction on my
part would perhaps ruin my schemes! Still more embarrassing would it be
should Bull, who cannot endure a black look, find himself muzzle to
muzzle with a rival and try to get quits with him by flying at his
throat. I should have to put an end to the fray, to avoid the scandal
of a well-brought-up Dog showing intolerance of the village cur. The
squabble would end in the breakdown of all my experimental scaffolding.
And to think that the eager preoccupations of a person not entirely
devoid of sense may sometimes be dependent on a Dog-fight!
Lord be praised, the road is deserted! The journey is accomplished
without hindrance; the thread, my great anxiety, does not break; the
egg is not bruised; everything is in order. The little clod of earth is
put in a place of safety, with the cell in a horizontal position. I
distribute near the egg two or three of the grubs which I have
collected; the complete allowance of provisions would cause trouble,
now that the cell possesses only half its enclosing wall and is reduced
to a semicylinder. Two days later, I find the egg hatched. The young
larva, yellow in colour, is hanging by its hinder end, head downwards.
It is busy with its first grub, whose skin is already growing limp. The
suspension-cord consists of the short thread that supported the egg,
with the addition of the slough, now reduced to a sort of crumpled
ribbon. In order to remain sheathed in the end of this hollow ribbon,
the hinder end of the new-born larva is at first slightly constricted
and then swells into a button. If I disturb it while at rest, or if the
victuals move, the larva withdraws, shrinking back upon itself, but
without retreating into the ascending-sheath, as does the Eumenes’
larva. The tethering-cord does not serve as a scabbard, as a refuge
into which the larva can retire; it is rather an anchor-chain, which
gives it a purchase on the ceiling and enables it to protect itself by
shrinking to a safe distance from the heap of victuals. When things are
quiet, the larva lengthens out and returns to its grub. Thus do matters
happen at the start, according to my observations, of which some were
made at home, in my rearing-jars, and others on the spot, when I
unearthed cells containing a larva young enough for my purpose.
The first grub is devoured in twenty-four hours. The larva thereupon,
so it seemed, goes through a moult. For at least some time it remains
inactive and contracted; then it releases itself from the cord. It is
now free, in contact with the heap of grubs and henceforth unable to
step out of the way. The life-line has not lasted long; it protected
the egg and safeguarded its hatching; but the larva is still very weak
and the peril has not diminished. This means that we shall discover
other means of protection.
By a very strange exception, whereof so far I know no other instance,
the egg is laid before the provisions are stored. I have seen cells
which as yet contained absolutely nothing in the way of victuals and
which nevertheless had the egg swinging from the ceiling. I have seen
others, also furnished with the egg and so far containing only two or
three head of game, a first instalment of the abundant dish of
twenty-four. This early egg-laying, so utterly unlike what happens in
the case of the other predatory Wasps, has its underlying motive, as we
shall see; it has its logic at which we cannot fail to marvel.
The egg, laid in the empty cell, is not fixed at random on the first
spot that offers upon the enclosing wall, which is vacant at all sides;
it is hung near the far end, opposite the entrance. Réaumur had already
noted this position of the budding larva, but without insisting on a
detail whose importance he did not suspect:
“The grub,” he says, “is born at the bottom of the hole, that is,
at the back of the cell.”
He does not speak of the egg, which he does not appear to have seen.
This position of the grub was so well known to him that, wishing to
attempt the rearing of a grub in a glass cell made with his own hands,
he placed the larva at the bottom and the victuals on top of it.
Why do I linger over a petty detail which the famous historian of the
Odyneri tells in half-a-dozen words? A petty detail? It is nothing of
the kind; on the contrary, it is a circumstance of paramount
importance. And this is why: the egg is laid at the back, necessitating
an empty cell which will be victualled after the egg is laid. The
provisions are now stored, piece by piece, layer upon layer, in front
of the egg; the cell is crammed with game right up to the entrance,
which in the end is sealed.
Of all these pieces, the obtaining of which may take several days,
which are the earliest in point of date? Those nearest the egg. Which
are the latest? Those by the entrance. Now it is obvious—besides, it
may be proved, if necessary, by direct observation—it is obvious, I
say, that the heaped worms lose strength from day to day. The effects
of a prolonged fast would be enough to produce this result, to say
nothing of the disorders due to a wound which becomes worse as time
goes on. The larva born at the back of the cell has therefore beside
it, in its first youth, the less dangerous provisions, the oldest in
date and consequently the feeblest. As it works its way through the
heap, it finds more recent game, which is also more vigorous; but this
is attacked without danger, because the larva’s own strength has come.
This progress from the more to the less nearly mortified victims
presumes that the grubs do not disturb the order in which they have
been stacked. That in fact is what happens. Former historians of the
Odyneri have all remarked that the grubs provided for the larva are
curled in the shape of a ring:
“The cell,” says Réaumur, “was occupied by green rings, to the
number of eight or twelve. Each of these rings consisted of a
vermiform larva, alive, curled up and with its back fitting exactly
against the wall of the hole. These grubs, laid in this way one on
top of the other and even pressed together, had no liberty of
movement.”
I, in my turn, remark similar facts in my two dozen grub-worms. They
are curled in a ring; they are stacked one upon another, but with a
certain confusion in the ranks; their backs touch the wall. I will not
attribute this circular curve to the effect of the sting which was very
probably administered, for I have never observed it in the caterpillars
stabbed by the Ammophilæ; I believe rather that the position is natural
to the grub during inaction, even as it is natural for the Iuli [25] to
coil themselves into a spiral. In this living bracelet there is a
tendency to return to the rectilinear conformation; it is a bent bow
fighting against the obstacle that surrounds it. By the very fact,
therefore, of being curled up, each grub keeps more or less steady by
pressing its back a little against the wall; and it retains its place
even when the cell approaches the vertical.
Moreover, the shape of the cell has been calculated with a view to this
manner of storing. In the part next the entrance, the part which one
might call the store-room, the cell is cylindrical and narrow, so as to
afford the living rings as little space as possible; they are thus kept
in position and are unable to slip. It is here that the grubs are
stacked, squeezed one against the other. At the other end, near the
back, the cell expands into an ovoid to give the larva elbow-room. The
differences between the two diameters is very perceptible. At the
entrance I find only four millimetres: [26] at the back I find six.
[27] Thanks to this inequality of width, the cell comprises two
apartments: the provision-store in front and the dining-room behind.
The Eumenes’ spacious cupola does not permit of this arrangement; there
the game is heaped up in disorder, the oldest in date promiscuously
with the most recent; and each piece is merely bent, not rolled. The
ascending-sheath provides a remedy for the disadvantages of this
confusion.
Note also that the packing of the victuals is not the same from one end
of the Odynerus’ skewerful to the other. In the cells whose provisions
have not yet or have only recently been broached, I observe this
detail: near the egg or the newly-hatched larva, in the part which I
have just described as the dining-room, the space is not fully
occupied; there are just a few grubs here, three or four, somewhat
isolated from the bulk and leaving enough room to ensure the safety of
either the egg or the young larva. This is the food supplied for the
early meals. If there be danger in the first mouthfuls, which are the
most risky of all, the life-line provides a means of withdrawal. More
towards the front, the game is piled in close-packed layers, the stack
of worms is continuous.
Will the larva, now that it possesses a modicum of strength, force
itself imprudently into this heap? Far from it. The victuals are
consumed in due order, from the bottommost to the topmost. The larva
drags towards it, to a little distance, into the dining-room, the first
ring that offers, devours it without danger of being inconvenienced by
the others and thus, layer by layer, consumes the batch of two dozen,
always in complete security.
Let us retrace our steps and end with a brief summary. The large number
of grubs provided for a single cell and their very incomplete paralysis
jeopardize the security of the Wasp’s egg and of her new-born larva.
How is the danger to be averted? This is the problem; and it has
several solutions. The Eumenes, with her sheath, which enables the
larva to climb back to the ceiling, gives us one; the Odynerus, in her
turn, gives us hers, a solution no less ingenious and much more
complicated.
The egg and also the newly-hatched larva have to be saved from the
danger of contact with the game. A suspension-thread solves the
difficulty. Up to this point, that is the method adopted by the
Eumenes; but soon the young larva, having eaten its first grub, drops
off the thread that gave it a support whereby to shrink out of harm’s
way. A sequence of conditions now begins, all directed towards its
welfare.
Prudence demands that the very young larva shall first attack the most
inoffensive of the grubs, that is those most nearly deadened by
abstinence, in short, the grubs first placed in the cell; it demands,
moreover, that the consumption of these grubs shall proceed from the
oldest specimens to the most recent, so that the larva may have fresh
game to the end. With this object, a curious exception is made to the
general rule: the egg is laid before the victualling is commenced. It
is laid at the back of the cell; in this way, the stacked provisions
will present themselves to the larva in due order of date.
That is not enough: it is important that the grubs shall be unable, in
moving, to alter their respective positions. This circumstance is
provided for: the store-room is a narrow cylinder in which change of
place is difficult.
Even that is not sufficient: the larva must have room enough to move
about at ease. The condition is fulfilled: at the back, the cell forms
a comparatively spacious dining-room:
Is that all? Not yet. The dining-room must not be encumbered like the
rest of the cell. The matter has been seen to: the first course
consists of a small number of specimens.
Have we done? By no means. It is not of any use to have a narrow
cylinder for the larder: if the grubs straighten out, they will slip
lengthwise and disturb the nurseling in the back-room. This has been
remedied: the game selected is a larva which deliberately rolls itself
into a bracelet and maintains its position by its own tendency to
unbend.
It is by the ingenious removal of this series of difficulties that the
Odynerus succeeds in leaving a family. We have seen enough of her
exquisite foresight to amaze us. What would it be were nothing to
remain concealed from our dull eyes!
Can the insect have acquired its skill gradually, from generation to
generation, by a long series of casual experiments, of blind gropings?
Can such order be born of chaos; such foresight of hazard; such wisdom
of stupidity? Is the world subject to the fatalities of evolution, from
the first albuminous atom which coagulated into a cell, or is it ruled
by an Intelligence? The more I see and the more I observe, the more
does this Intelligence shine behind the mystery of things. I know that
I shall not fail to be treated as an abominable “final causer.” Little
do I care! A sure sign of being right in the future is to be out of
fashion in the present.