THE NUT-WEEVIL
If a peaceful home, a good stomach and a secure livelihood are enough
to bring happiness, then the Nut-weevil is truly a happy creature, more
so even than the famous Rat who retired into a Dutch cheese. The hermit
of the fabulist [41] had kept up certain relations with the world, the
source of all his troubles. One day, a deputation from the Rat folk
came to ask him for a trifling alms. The recluse listened to their
complaints with an unwilling ear; he told them that he could not help
them, promised to pray for them and shut the door without further ado.
Hard though he was upon the needs of others, this visit of famished
beggars must have disturbed his digestion somewhat: history does not
tell us so, but we are at liberty to believe it. The hermit of the
naturalist is not subject to these annoyances. Its dwelling is an
inviolable cell, a coffer made all in one piece, with neither door nor
wicket for distressed bores to come knocking at. Within is absolute
quiet, nothing enters of the sounds or cares of the outer world. An
excellent lodging, neither too hot nor too cold, peaceful and closed to
all. An excellent table, besides, and a sumptuous. What more could any
one ask for? The smug inmate waxes big and fat.
We all know the rascal. Which of us, when a boy, cracking a hazel-nut
with his strong teeth, has not bitten into something acrid and sticky?
Ugh! It’s the nut-maggot! Let us conquer our repugnance and examine the
creature closely. It is worth the trouble.
We see a plump and lusty grub bent into a bow, legless and milk-white,
except the head, which is capped with a yellowish horn. When taken from
its cell and laid on the table, the thing wriggles about, coiling and
uncoiling and fidgeting without contriving to shift its place. It is
denied the power of locomotion. What would the worm do with that power,
boxed up as it is? For that matter, this is a feature common to the
Weevil tribe, all of whom are inveterate stay-at-homes in their larval
stage. Such is the hermit whose history follows below, the anchorite
with the sleek and rounded rump, the larva of the Nut-weevil (Balaninus
nucum, Lin.).
The kernel of the hazel-nut is its cake, an abundant provision, which
it never or but very seldom finishes entirely, so greatly do the
victuals exceed the utmost requirements of obesity. There is plenty to
enable one alone to live comfortably for three or four weeks; but it
would mean short commons for two. And so the victuals are scrupulously
rationed: to each nut its grub, no more.
I have happened on very rare occasions to find two. The late-comer, the
offspring of some ill-informed mother, had seated itself at table
beside the other, without much profit to itself. There was not much
left of the cake; moreover, the still feeble intruder seemed to have
had a bad reception from the powerful and jealous owner of the
property. There was no doubt about it: the superfluous weakling was
doomed to perish. The Weevil knows no more of mutual aid among kinsmen
than the Rat in the cheese. Each for himself: such is the savage and
bestial law, even in a nutshell.
The dwelling is a perfectly continuous fortification, without a joint
or fissure for an invader to slip through. The walnut-tree forms the
shell of its fruit out of two halves joined together, with a line of
least resistance left between them; the hazel makes its kegs with a
single stave, curved into an arch that is equally strong at all points.
How did the grub of the Balaninus obtain access to this fortress?
On the surface, smooth as polished marble, the eye perceives nothing to
explain the entrance of an exploiter from without. One can picture the
surprise and the artless imaginings of those who first remarked the
peculiar contents of the intact nut, without any sort of opening to it.
The plump maggot, living inside it, could not be an alien. It was
therefore born of the fruit itself, under the influence of an unlucky
moon. It was a child of putrefaction hatched by a mist.
A faithful custodian of the ancient beliefs, the peasant of to-day
always attributes maggoty nuts and other fruits spoiled by insects to
the moon and a passing miasma. And this will be so indefinitely, until
our country schools yield the place of honour to cheerful, invigorating
studies in the fields.
Let us replace these inanities by the reality. The grub is certainly an
outsider, an invader; and, if it has made its way in, this is because
it has found a passage somewhere. Let us look for this passage, which
escaped us at the first examination, with the aid of a
magnifying-glass.
The search does not take long. The base of the nut displays a wide,
rough, light-coloured depression, to which the cup was fastened. On the
confines of this area, a little way outside it, is a darker speck. Thus
is the entrance to the stronghold; this is the key to the riddle.
The rest follows without further inquiry and is very clearly
interpreted by the data provided by the Elephant Weevil. The Nut-weevil
also bears a buccal drill, still inordinately long, but this time
slightly curved.
I can well imagine the insect, like its relative of the acorns,
standing erect on the tripod formed by the tip of its wing-covers and
the hinder tarsi; it assumes a posture worthy of portrayal by a
fantastic pencil; it plants its instrument perpendicularly; it
patiently veers and veers again.
The work is arduous, very arduous, for the nut is selected when nearly
ripe, to provide the grub with more savoury and more abundant food; it
is thick and tough, much more so than the rind of an acorn. If the
Acorn-weevil takes half a day to bore her passage, how long must the
Nut-weevil’s task be, how patient her persistence! Perhaps her rod is
specially hardened. We can temper our drills till they wear away
granite; no doubt the Weevil, in the same way, provides her boring-tool
with a bit of triple hardness.
Quickly or slowly, the auger sinks into the base of the nut, where the
tissues are softer and milkier; it enters obliquely, making a fairly
long journey, to prepare for the grub a column of semolina suited to
its first needs. Whether boring into nuts or into acorns, the Balanini
make the same delicate preparations for the benefit of their offspring.
At length there comes the placing of the egg, right at the bottom of
the shaft. Here the strange method which we already know is repeated.
With a hinder rostrum, equal in length to the front one and kept hidden
away in the abdomen until the moment comes for using it, the mother
inserts her egg at the base of the kernel.
I see these nursery precautions only in my mind’s eye, but I see them
very clearly, enlightened as I am by my examination of the nut
converted into a cradle and above all by the method of the
Acorn-weevil. Still, I might aim at something better than this; I
should like to witness the operation: rather a hopeless ambition, I
fear.
In my neighbourhood, indeed, the hazel is scarce and its regular
exploiter is almost unknown. Nevertheless, let us make the experiment
with the six hazel-trees which I planted in the paddock long ago. First
of all we must stock them accordingly.
A valley of the Gard, less parched than the Sérignan hills, provides me
with a few couples of the insect. They reach me by post at the end of
April, when the nut, still quite light in colour, soft and flattish, is
beginning to emerge from the cup in which it is sheathed. The kernel is
far from formed; there is just a beginning, a promise of a kernel.
In the morning, in glorious weather, I put the strangers on the leaves
of my hazels. The journey has not tried them unduly. They look splendid
in their modest drab costume. The moment they are free, they half-open
their wing-cases, spread their wings, fold them again and once again
unfurl them, without taking flight. These are mere muscular exercises,
serving to revive their strength after a long imprisonment. I regard
these sports in the sunlight as a good omen: my colonists will not run
away.
Meantime the nuts are filling out daily and beginning to tempt and
entice the children. They are within reach of the smallest, who love to
stuff their pockets with them and to crunch them, cracking them between
two stones. They receive express injunctions to keep their hands off
them. This year, for the sake of the Weevils whose history I wish to
learn, the joys of gathering nuts in May will be forbidden.
What sort of ideas can such a prohibition produce in these ingenuous
minds? If they were of an age to understand me, I would say:
‘My dears, beware of the great enchantress, Science. If ever one of
you—which Heaven forbid—should allow himself to be beguiled by her, let
him remember my warning: in exchange for the little secrets which she
reveals to us, she demands much graver sacrifices than a handful of
nuts.’
The prohibition is understood; the tempting fruit is left almost
untouched. For my part, I inspect the nuts assiduously. All my trouble
is unavailing: I do not succeed in surprising a Balaninus engaged in
her patient task of boring. At the utmost, at sunset, I happen to see
one who, hoisted to her full height, is trying to insert her drill. The
little that I observe teaches me nothing new; the Acorn-weevil has
already shown me as much.
In any case, it is only a brief attempt. The insect is casting about
and has not yet found what suits her. Perhaps the perforator of
hazel-nuts works at night.
In another respect I have been more fortunate. Some nuts, some of the
first colonized, are laid by in my study and subjected to frequent
inspections. My diligence is rewarded with success.
At the beginning of August, two larvæ leave their coffers before my
eyes. They have no doubt long been chipping with the points of their
mandibles, that patient chisel, at the hard wall. The exit-hole is just
finished when I take note of the coming departure. A fine dust is
falling by way of shavings.
The window of release is distinct from the narrow aperture of the
entrance. Perhaps it will not do to obstruct this grating, which
ventilates the house, while the grub is still at work. The window
aforesaid is situated at the base of the fruit, close to the rough
surface by which the nut adheres to its cupule. In this region, where
the incipient materials are elaborated until the nut is perfectly ripe,
the density is a little less than elsewhere. The point to be perforated
is excellently chosen therefore: it is here that the least resistance
will be encountered.
Without any preliminary auscultation, without exploratory soundings,
the recluse knows the weak point of his prison. Confident of success,
he works away with a will. Where the first blow of the pick is struck
the others follow; no time is wasted on experiments. Persistence is the
strength of the weak.
It is done: daylight enters the coffer. The window is opened, round,
widening a little inwards and carefully polished over the whole
circumference of its embrasure. Under the burnisher of the mandibles
any roughness that might presently increase the difficulty of the
emergence has disappeared. The holes in our steel draw-plates are
scarcely more accurate.
The comparison with a draw-plate comes in quite aptly here: the larva
actually frees itself by a wire-drawing-operation. Like a length of
brass wire which is reduced by being passed through an orifice too
narrow for its diameter, it escapes through the window in the shell by
decreasing its girth. The wire is drawn by an exertion on the part of
the workman’s pincers or by the rotation of the machine; it
subsequently retains the reduced thickness which the operation has
given it. The grub knows another method: it lengthens and thins itself
by its own efforts; and, directly it has passed through the narrow
orifice, it returns to its natural size. Apart from these differences
the resemblance is striking.
The exit-aperture is precisely the same width as the head, which, being
rigid, with a horny cap, does not lend itself to deformation. Where the
head has passed, the body has to pass, however fat it may be. When the
liberation is completed, it is most surprising to see how bulky a
cylinder, how corpulent a grub has contrived to make its way through
the tiny opening. If we had not witnessed the exodus, we should never
have suspected such a feat of gymnastics.
The orifice, we were saying, is exactly fitted to the diameter of the
head. Now this inelastic head, by whose size that of the hole has been
calculated, represents at most one-third of the width of the body. How
does a threefold thickness pass through a single calibre?
Here comes the head, without the least difficulty: it is the pattern to
which the door was built. The neck, a little wider, follows: a slight
contraction frees it. Next comes the turn of the chest and the plump
belly. This is a most arduous operation. The grub has no legs. It has
nothing, neither hooks nor stiff bristles, that might give it a
purchase. It is a soft roly-poly which has, by its own efforts, to
clear the disproportionately narrow passage.
What happens inside the nut escapes me: it is hidden by the opaque
shell; what I see outside is very simple and tells me of that which
cannot be seen. The creature’s blood rushes from back to front; the
humours of the organism change their position and accumulate in the
part that has already emerged, which swells into a dropsy, attaining
five or six times the diameter of the head.
In this way a large cushion is formed on the kerb of the well, a girdle
of energy which, by its dilatation and its intrinsic elasticity,
gradually extricates the remaining segments, which are diminished in
volume by the shifting of their fluid contents.
It is a slow and very laborious business. The grub, in its free part,
bends, draws itself up and sways from side to side. We do the same when
forcing a nail from side to side to extract it from its socket. The
mandibles gape widely, close and gape again, with no intention of
laying hold. These movements represent the yo-heave-hoes with which the
exhausted creature accompanies its efforts, like those of sailors
hauling on a cable.
‘Yo-heave-ho!’ says the grub; and the sausage rises a peg higher.
While the extracting pad is swelling and straining every muscle, it is
evident that the part still in the shell is draining itself of its
humours as far as it possibly can, making them flow into the part
released. It is this that makes the wire-drawing action feasible.
One more effort of leverage from the inflated girdle; one more yawn:
‘Heave-ho!’
That has done the trick. The grub glides over the shell and drops.
One of the nuts which have just afforded me this sight was gathered on
its branch a few hours before. The grub, then, would have fallen to the
ground from the height of the hazel-bush. Allowing for the proportions,
such a fall would for us mean a terrible crash; for the grub, so
plastic and supple, it is a trifle. It matters little to the larva
whether it tumbles into the world from the top of the bush or whether
it quietly changes its lodgings a little later, when the nut, fallen of
its own ripeness, is lying on the ground.
Without delay, as soon as free, it explores the soil within a
restricted radius, seeks a point easy to dig, finds it, does a little
spade-work with its jaws, wriggles its rump and buries itself. At no
very great depth a spherical cavity is made by pressing back the dusty
soil. Here the grub will spend the winter and await the resurrection of
the spring.
Were I so presumptuous as to advise the Balaninus, better-versed than
any one in its business as a Weevil, I should say:
‘To leave your nut now is an act of folly. Later, when the April
festival is here and the hazels replace their drooping catkins by the
pink pistils of their nascent fruit, well and good; but to-day, in this
time of blazing sunshine, which drives the most gallant workers to
idleness, what is the use of deserting a home in which you can sleep so
comfortably throughout the slack summer season? Where will you find a
better lodging than the shell of a hazel-nut when the autumn rains come
and the winter frosts? In what more peaceful solitude could the
delicate work of the transformation be effected? Besides, the subsoil
is full of dangers. It is damp and cold; its roughness makes it painful
to the touch for a skin as fine as yours. A formidable enemy lurks
there, a cryptogam that implants itself upon any buried larva. In my
jars I have great difficulty in protecting the buried larvæ which I am
trying to rear. Sooner or later white tufts form upon the glass wall,
thread-like fluffs whose lower portion will clasp and drain a poor grub
turned into a scrap of plaster: it is the mycelium of one of the
Sphæriaceæ whose allotted field of exploitation is the bodies of
insects undergoing nymphosis underground. In the nut, a hygienic cell,
free from devastating germs, nothing of the sort is to be feared. Why
leave it?’
These arguments the Balaninus meets with a refusal. It shifts its
quarters, and it is right. On the ground, where the nut is lying, it
has reason, to begin with, to dread the Field-mouse, a great hoarder of
nuts. He collects in his stone-heap everything yielded by his nightly
rounds; then, at his leisure, with a patient tooth, he pierces a small
hole in the shell and extracts the kernel.
The hazel-nut is a welcome find, a savoury morsel. If emptied by the
Weevil, it is only the more valuable: instead of its usual contents it
contains the grub of the Balaninus, a rich saveloy which makes a
pleasant change from a farinaceous diet. So, for fear of the
Field-mouse, we go underground.
A still more important motive urges this departure. True, it would be
pleasant to sleep in the impregnable castle of the nut-shell; but the
delivery of the future insect has also to be thought of. The larva of
the Capricorn, throwing caution to the winds, leaves the interior of
the oak and comes to the surface, risking the investigations of the
Woodpecker; it runs into danger to prepare an exit for the great horned
Beetle, who could not make his way out unaided.
A similar precaution is necessary for the Weevil-larva. While
possessing the full strength of its mandibles, without waiting for the
torpor during which the accumulated fats will be remoulded into a new
organism, it pierces the coffer from which the adult would be incapable
of escaping by her own efforts; it comes out and buries itself in the
ground. The future is wisely provided against; from its present
catacomb the adult will be able without hindrance to ascend to the
light of day.
We were saying that, if the Weevil assumed her final shape in the nut,
she would be incapable of effecting her own release. Yet with her drill
she is very well able to perforate the shell when the egg has to be
installed. Why should she be prevented from doing in the inverse
direction what she is able to perform inwards from without? A little
reflection will show us the tremendous difficulty.
To place the egg in position, a fine tube, of the thickness of the
drill, is sufficient. To give passage to the solid adult Weevil would
demand a comparatively enormous opening. The material to be pierced is
very hard, so hard that the larva, with the powerful gouges of its
mandibles, bores a hole only just big enough to allow the head to pass.
The rest of the body has to follow by dint of exhausting efforts.
How could the insect open a sufficiently large door with its delicate
foil, when the far better-equipped grub has so much difficulty in
boring a moderate porthole? Could she not, by making a ring of
perforations, remove a round disk of the requisite size? Strictly
speaking, this would be possible, with a prodigious expenditure of
patience, a quality which insects can hardly be said to lack.
But here length of time is not enough: the boring-tool is absolutely
unmanageable inside the nut-shell. It is so long that, to implant it at
the point to be drilled, the Weevil, when she works outside, is obliged
to stand erect. For lack of space under the low ceiling of the shell,
this position and the alternate tacking about become impossible.
However patient she herself may be and however well-armed we suppose
the tip of her drill to be, the Weevil, prevented from employing her
auger by the narrowness of the premises, would perish in her coffer.
She would die a victim to her inordinate machinery, which serves
excellently well for pushing the egg into place, but which would be
very unwieldy if the prisoner had to effect her own delivery.
Given a less exaggerated rostrum, just a short and powerful punch, the
Weevil, methinks, would not abandon the nut while she was still in the
larva stage, the danger of the Field-mouse notwithstanding. It is a
delightful laboratory for the remodelling-process of the metamorphosis.
The shell, it is true, lies on the surface of the soil, unsheltered and
exposed to the north-wind. But what does the cold matter, provided that
we keep dry? The insect has little to fear from the frosts. Its
slumbers are all the sweeter when the torpor attending the renewal of
its being is increased by the torpor due to a low temperature.
I am persuaded of it: if she carried a less cumbersome drill, the
Balaninus would not change her quarters the moment the kernel of her
hazel-nut was consumed. My conviction is based on the habits of other
Weevils, in particular Gymnetron thapsicola, Germ., who exploits the
capsules of a mullein, Verbascum thapsus, Lin., the shepherd’s club, a
frequent denizen of the tilled fields. As cells these capsules are,
though less in volume, almost the equivalent of the hazel-nut.
They consist of strong shells, formed of two pieces closely joined,
with no communication whatever with the outside world. A Weevil of
humble size and modest attire takes possession of them in May and June
as lodgings for her larvæ, which gnaw the placenta of the fruit, laden
with unripe seeds.
In August the plant is withered, scorched by the sun, but still
standing and topped with its compact spike of capsules. Open some of
these shells, almost as solid as cherry-stones. Inside is the Weevil in
the adult state. Open them in winter: the Gymnetron has not gone. Open
them for the last time in April: the little Weevil is still at home.
Meanwhile, fresh mulleins have sprouted hard by; they flower; their
shells attain the right degree of ripeness: the time has come to leave,
to go and establish one’s family. Not till then does the solitary
demolish her hermitage, her capsule, which has protected her so
faithfully hitherto.
And how does she do so? It is quite simple. Her rostrum is a short
bradawl, easily wielded therefore, even in the confined space of a
cell. The shell, moreover, is not too strong. It is a very dry vellum
wrapper rather than a hard wooden wall. The recluse drives her
short-handled pick into it; she stabs and thumps and brings the wall
crumbling down. And now hurrah for the joys of the sun! Hurrah for the
yellow flowers, with stamens all bristling with violet hairs!
Considering their tools, in one case of exaggerated length under a too
low ceiling, in another short and suited to the space available in the
cell, are not both these insects happily inspired, the first in leaving
her nut prematurely, while the grub’s powerful shears enable her to do
so, the second in spending three parts of the year in the security of
her shell, quitting it only at the time of the wedding on the friendly
plant? Thus do we see the impeccable logic of the instincts revealed,
even in the humblest creatures.