OTHER LEAF-ROLLERS
Is the insect’s trade determined by the nature of the tools of which it
disposes, or, on the contrary, is it independent of them? Does the
organic structure govern the instincts, or do the insect’s various
aptitudes hark back to origins that cannot be explained merely by the
details of its anatomy? We shall obtain an answer to these questions
from two other leaf-rollers, the Apoderus of the Hazel (A. coryli,
Lin.) and the Attelabus (A. curculionoides, Lin.), both of them eager
rivals of the cigar-makers who work the poplar and the vine.
According to the Greek lexicon, the term Apoderus ought to mean ‘the
flayed.’ Is this really what the author of the expression had in mind?
My few books, the odd volumes of a village naturalist, do not enable me
to reply. However, to me the word is explained by the insect’s colour.
The Apoderus is a skinless creature, displaying its naked and bleeding
misery. Its colour is vermilion, as bright as sealing-wax. It is like a
drop of arterial blood coagulated on the dark green of a leaf.
To this loud costume, rare among insects, are added other, equally
unusual characteristics. The Weevils are all microcephalous. This one
exaggerates the absurd disproportion even further: she retains only the
indispensable minimum of a head, as though she were trying to do
without one altogether. The cranium in which her poor brain is lodged
is a paltry, glittering, jet-black speck. In front of this speck is no
beak, but a very short, wide snout; behind is an unsightly neck, which
one might imagine to have been strangled in a halter.
Standing high on her legs, clumsy in her gait, she ambles step by step
across her leaf, which she pierces with round windows. The material
removed is her food. Faith, a strange creature: a reminiscence, maybe,
of some ancient mould, cast aside by life’s progress!
Three Apoderi and no more figure in the European fauna. The best-known
is that of the hazel. This is the one to whom I propose to devote my
attention. I find her here, not on the hazel, her lawful domain, but on
the common alder. This change in her activities deserves a brief
investigation.
My district does not suit the hazel very well; the climate is
unfavourable, being too hot and dry. On the high slopes of Mont Ventoux
it grows sparsely; in the plain, except in the gardens where a few find
a footing, they are no longer to be seen. In the absence of the
fostering bush, the insect, without becoming impossible, is at least
extremely rare.
Long though I have been beating the brambles of my countryside over an
umbrella held upside down, here is our Apoderus for the first time. For
three springs in succession I see the red Weevil on the alder and
observe her work. One tree, one alone and always the same, in the
osier-beds of the Aygues provides me with this leaf-roller, whom I now
for the first time see alive. The other alders round about have not a
trace of her, though they are only a few yards distant. There is here,
on this privileged tree, a small, accidental colony, a settlement of
foreigners, who are becoming acclimatized before extending their
domain.
How did they come here? Undoubtedly brought by the torrent. The
geographers call the Aygues a water-course. As an eye-witness, I should
call it, more accurately, a pebble-course. Understand me: I do not mean
that the dry pebbles flow down it of themselves; the low gradient does
not permit of such an avalanche. But only let it rain; and they will
stream fast enough. Then I can hear the roar of the grinding stones
from my house, a mile and a quarter distant.
During the greater part of the year, the Aygues is a broad expanse of
white pebbles; of the torrent naught remains but the bed, a furrow of
enormous width, comparable with that of its mighty neighbour, the
Rhone. Let the rain fall persistently, let the snows melt on the slopes
of the Alps; and the thirsty furrow fills for a few days: roaring, it
overflows to a great distance and turbulently shifts its shoals of
pebbles. Return a week later. The roar of the flood is succeeded by
silence. The terrible waters have disappeared, leaving on the banks, as
the trace of their brief passage, wretched muddy puddles soon absorbed
by the sun.
These sudden freshets bring a thousand live gleanings swept off the
flanks of the mountains. The dry bed of the Aygues is a most
interesting botanical garden. There you may gather many vegetable
species brought down from the higher levels, some temporary,
disappearing without offspring in a single season, others persisting
and adapting themselves to the new climate. They come from far away,
from the heights, these exiles; to pluck this one or that in its true
environment you would have to climb Mont Ventoux, pass beyond the zone
of the beeches and reach the altitude where trees cannot grow.
Alien zoology in its turn is represented in the osier-beds, whose calm
is disturbed only during unusually prolonged floods. My attention is
attracted especially by the land-mollusc, that champion stay-at-home.
In stormy weather, when the thunder growls—lou tambour di cacalauso, as
the Provençal calls it—the most that the Snail permits himself in the
matter of moving about is to issue from his stronghold, some crevice in
the rocks, and to browse before his door upon the grasses, mosses and
lichens made tender by the flood. It takes a cataclysm to make that one
travel!
The wild freshets of the Aygues succeed in doing so. They bring into my
part of the world and deposit in the osier-thickets the largest of our
Snails, Helix pomatia, the glory of Burgundy. [45] Rolled down the
grassy mountain-slopes by the showers, the exile defies immersion
within the water-tight cover of his chalky operculum; he endures the
jolting, thanks to his strong shell. He travels by stages, from one
osier-bed to another. He descends as far even as the Rhone and
colonizes the Île des Rats and the Île du Colombier opposite the mouth
of the Aygues.
Whence does he come, this enforced emigrant, whom one would vainly seek
elsewhere in the land of the olive? He loves a moderate temperature,
green turf, cool shades. His place of origin is certainly not here, but
far away on the rounded heights of the lower, outermost Alps. The
highlander’s exile none the less seems pleasant. The big Snail does
quite well in the marshy scrub on the banks of the torrent.
Neither is the Apoderus a native. She is a castaway, hailing from the
hazel-clad heights. She has made the voyage in a little boat, that is
to say, in the leafy cockle-shell in which the grub is born. The vessel
was tightly closed, which made the passage possible. Running ashore at
some point on the bank in the height of summer, the insect perforated
its cell and, not finding its favourite tree, established itself upon
the alder. There it founded a family, remaining faithful to the same
tree for the three years during which I had to do with it. It is
probable, for that matter, that the origin of the settlement dates
farther back.
The history of this stranger interests me. The primordial conditions of
her life—climate and food—are changed. Her ancestors lived under a
temperate sky; they grazed on the leaf of the hazel-bush; they
manufactured cylinders out of piece-goods made familiar by the constant
practice of past generations. But the wanderer is living under a torrid
sky; she grazes on the alder-leaf, whose flavour and nutritive
properties must differ from those of the family diet; she works at an
unknown piece, though it is not unlike the normal piece in shape and
size. What changes has this disturbance of its diet and climate
effected in the insect’s characteristics?
Absolutely none. In vain I pass the magnifying-glass over the exploiter
of the alder and over the exploiter of the hazel-bush, of whom the
latter has reached me from the heart of the Corrèze by post. I see not
the least difference between the two, even in the smallest details. Can
the method of industry have been modified? Without seeing the work done
with a hazel-leaf, I boldly assert that it is similar to that obtained
with an alder-leaf.
Change the food and the climate, change the materials to be worked: if
it can adapt itself to the new conditions imposed upon it, the insect
persists, immutable in its craft, habits and organization; if it
cannot, it dies. To be as one was or not to be: that is what the
castaway of the torrent, like so many others, tells us.
Let us watch her at work on the alder and we shall know how she labours
on the hazel-bush. The Apoderus does not know the method of the
Rhynchites, who, to kill the elasticity of the leaf to be rolled, makes
a deep puncture in the stalk. The red leaf-roller has a special modus
operandi, in no way related to that of the puncture.
Can this change of method be due to the absence of the rostrum, of the
fine awl capable of being driven into the narrow leaf-stalk? It is
possible, but not certain, for the snout, an excellent pair of shears,
could cut half through the leaf-stalk at a bite and obtain an
equivalent result. I prefer to see in the novel procedure one of those
methods which are the separate property of every specialist. We must
never judge of the work by the tool employed. The insect is an adept at
using any sort of implement, even though defective.
The fact is that with her mandibles the Apoderus slashes the alder-leaf
cross-wise, at some distance from the base. The whole leaf is cut clean
through, including even the central vein. The only part left intact is
the extreme edge, from which the large severed area hangs withering.
This area, the greater part of the leaf, is then folded in two along
the principal vein, with the green or upper surface inside; then,
starting from the tip, the folded sheet is rolled into a cylinder. The
orifice above is closed with that part of the border which the cut has
left untouched; the orifice below is closed with the edges of the leaf
tucked inwards.
The pretty little barrel hangs perpendicularly, swaying to the least
breeze. It is hooped by the median vein, which projects at the upper
end. Between the second and third pages, as it were, of the double
sheet, near the middle of the spiral, is the egg, resin-red and, this
time, single.
The few cylinders which I have been able to examine afford me no
circumstantial details touching the development of their inmate. The
most interesting fact which I learn from them is that the grub, when it
has attained its full growth, does not go underground as the others do.
It remains in its barrel, which the wind soon shakes down into the
grass. That half-decayed shelter would be very unsafe in bad weather.
The red Weevil knows this. She hastens to assume her adult form, to don
her scarlet cloak; and by the beginning of summer she abandons her
cylinder, now a mere wreck. She will find a better refuge under the
loose strips of old bark.
Attelabus curculionoides is no less expert in the art of making a keg
out of a leaf. There is one curious point of resemblance: the new
cooper is red, like the other, or, more accurately speaking, crimson.
The rostrum is very short and expanded into a snout. Here the likeness
ceases. Our first friend is rather fine-drawn and loose-limbed; the
second is a thickset, round, dumpy Weevil. We are quite surprised by
her work, which seems incompatible with the worker’s awkward, clumsy
build.
And she does not work a docile stuff either: she rolls ilex-leaves,
young ones, it is true, not yet too stiff. It is a tough material all
the same, difficult to bend and slow in fading. Of the four
leaf-rollers of my acquaintance, the smallest, the Attelabus, has the
hardest lot; nevertheless, it is she, the dwarf, such a bungler in
appearance, who by dint of patience builds the prettiest house.
At other times she exploits the common oak, the English oak, whose
leaves are broader and more deeply indented than those of the ilex, or
holm-oak. On the spring shoots she selects the topmost leaves, of
average size and medium consistency. If the position suit her, five,
six or more little kegs will be dangling from the same twig.
Whether it settle on the holm-oak or on the common oak, the insect
begins by incising the leaf, at some distance from the base, to the
right and left of the median vein, while respecting the vein itself,
which will provide a solid attachment. Then the Apoderus’ method is
repeated: the leaf, rendered more tractable by the two incisions, is
folded lengthwise, with the upper surface inside. All these
leaf-rollers, cigar-makers and coopers alike, know how to overcome the
resilience of a leaf by means of punctures or incisions; all are
thoroughly versed in that principle of statics according to which the
surface whose elasticity is the greater will be found on the convex
aspect of the curve.
Between the two sheets which touch, the egg is laid, again one egg.
Then the double leaf is rolled from the tip to the attachment. The
indentations, the serrations of the last fold are sealed down by the
patient pressure of the snout; the two mouths of the cylinder are
closed by turning the edges in. It is finished. The barrel is
completed, about two-fifths of an inch long and hooped at its fixed end
by the median vein. It is small but strong and not devoid of elegance.
The thick-set cooper has her merits, which I should like to elucidate
more fully by watching her at work. What I have contrived to see in the
open, in the actual workshop, amounts to little more than nothing. Many
a time do I surprise the Weevil on her cask, motionless, with her snout
against the staves. What is she doing there? She is sleeping in the
sunlight; she is waiting for the last layer of the work to acquire a
firm hold under prolonged pressure. If I examine her too closely, she
at once gathers her legs under her belly and lets herself fall.
Since my visits tell me hardly anything, I try to rear the insect in
domesticity. The Attelabus lends herself very well to the attempt: she
works under my bell-jars as zealously as on her oak. What I now learn
deprives me of all hope of following the details of the leaf-rolling
process: the Attelabus is one of those who work at night.
Late in the evening, about nine or ten o’clock, she gives the cuts of
the scissors that slash the leaf; next morning the keg is finished.
Seen by the uncertain light of a lamp and at untimely hours, hours
rightly claimed by sleep, the worker’s delicate technique would escape
me. We will give up the idea.
There is a reason for these nocturnal habits. I think I see what it is.
The leaf of the oak, especially of the holm-oak, is much harder to bend
than the leaf of the alder, the poplar or the vine. If rolled in the
daytime, under the burning rays of the sun, it would add to the
difficulties arising from indifferent flexibility those due to
incipient dryness. On the other hand, when visited by the dew, in the
coolness of the night, it will remain pliable; it will yield adequately
to the efforts of the roller; and the barrel will be ready when the sun
comes, with its blazing heat, to steady the shape of the still moist
fabric.
However different one from the other, the four leaf-rollers have shown
us that the individual craft is not a matter of organic structure, that
the tool does not determine the nature of the work. Whether endowed
with a rostrum or a snout, whether long-legged or slow, slender or
thickset, perforators or cutters-out, they all four achieve the same
result, the cylinder that acts as a shelter and a larder for the grub.
They tell us that instinct has its origin elsewhere than in the organs.
It goes farther back; it is inscribed in the primeval code of life. Far
from being dependent on the tools, it commands them and is able to
employ them as it finds them, with the same skill, for one task here
and for another there.
The little cooper of the oak-tree has not finished with her
revelations. Having observed her pretty frequently, I know how
fastidious she is of the quality of her victuals. If they be dry, she
refuses them absolutely, even though it means dying of starvation. She
wants them tender, pickled in moisture, softened by incipient decay,
even seasoned with a touch of mildew. I prepare them to her liking by
keeping them in a jar on a bed of moist sand.
Thus treated, the grub hatched in June soon increases in size. Two
months are enough to turn it into a handsome orange-yellow larva,
which, when its cell is broken open, suddenly, with the violence of a
spring released, straightens its curved body and tosses about. Observe
its slender form, much less stout than that of the other Weevils in
general. This is the only instance in which lack of corpulence in the
larva denotes an adult of an exceptional class. I shall say no more on
the subject of the grub: its description would be of no particular
interest.
The matter deserves looking into more closely. It is the end of
September; we have been suffering from an extraordinarily hot and dry
summer. The dog-days seem determined to last for ever. The forests are
ablaze in the Ardèche, the Bordeaux and the Roussillon districts; whole
villages have been burnt down on the slopes of the Alps; in front of my
door, a careless passer-by, throwing away a match, sets fire to the
neighbouring meadows. You cannot call it a summer: it is a
conflagration.
What can the Attelabus be doing in such disastrous weather? She is
thriving comfortably in my jars, which keep her victuals soft for her;
but, at the foot of her oak, amid the undergrowth shrivelled as though
by the breath of a furnace, on the calcined earth, what becomes of the
poor thing? Let us go and see.
Beneath the oaks which she was exploiting in June, I succeed in
finding, among the dead leaves, a dozen of her little barrels. They
have retained their green colour, so suddenly did the desiccation seize
them. They crack and crumble into dust under the pressure of the
fingers.
I open a barrel. In the middle is the grub, looking fit enough, but how
small! It is hardly larger than when it left the egg. Is it dead or
alive, this yellow atom? Its immobility proclaims it to be dead; its
unfaded colour proclaims it to be alive. I break open a second barrel,
a third. In the middle there is always a yellow grub, motionless and
quite small, as though newly-born. We will stop at this and keep the
rest of my collection for an experiment that occurs to my mind.
With their mummy-like immobility, are the grubs really dead? No; for,
if I prick them with the point of a needle, they twitch immediately.
Their condition is merely one of arrested development. In their
freshly-rolled sheath, still hanging from the tree and receiving a
little sap, they found the food necessary for their early growth; then
the barrel fell to the ground, where it soon dried up.
Then, disdaining its hard provender, the grub ceased to eat and grow.
Who sleeps dines, so the proverb says; and it is waiting in a state of
torpor for the rain to soften its bread.
This rain, for which man and beast have been sighing for four months
past, I have it in my power to realize, at least to the limits of a
Weevil’s requirements. I float the rest of the dry barrels in water.
When they are thoroughly soaked, I transfer them into a glass tube,
closed at either end with a plug of wet cotton-wool which will keep the
atmosphere moist.
The result of my stratagems deserves mention. The sleepers awake, eat
the inside of the softened loaf, and make up so well for lost time that
in a few weeks they are as large as those which have not suffered any
interruption in my jars half full of moist earth.
This knack of suspending life for months at a time, when the provisions
have lost the requisite tenderness, is not repeated in the other
leaf-rollers. At the end of August, three months after the hatching,
there is nothing left alive in the cigars of the vine which have been
allowed to dry. Death is even swifter in the withered cigars of the
poplar. As for the cylinders of the alder, in the absence of a
sufficient number of leaves, I was not able to estimate their
inhabitants’ powers of endurance.
Of the four leaf-rollers, the one most threatened by drought is that of
the oak. Her barrel falls and lies on a soil which is extremely arid
except at times of rain; moreover, because of its small dimensions, it
dries right through at the first touch of the sun.
The ground is equally dry in the vineyard; but there is shade under the
branches, and the generous cigar is thick enough to retain in its
central part, far better than the slender barrel does, a little of the
moisture indispensable to the grub. In respect of prolonged abstinence,
the Vine-weevil cannot be compared with the barrel-maker; still less
can the Poplar-weevil. For this last, more often than otherwise, there
is no danger from drought, despite the smallness of the cylinder, a
sorry rat’s-tail. This roll usually falls by the side of a ditch, on
the moist soil of the meadows. The exploiter of the alder is hardly in
danger either: at the foot of her tree, a lover of the trickling
brooks, she finds the coolness needed to keep her food-cylinder in good
condition. But, when she exploits the hazel-bush, I do not know what
conditions help her out of her difficulty.
Lately the newspapers, which noisily echo every piece of absurdity,
have been making a certain fuss about the gastric feats of a few poor
devils who, to earn their bread, have fasted for thirty or forty days.
As in most stunts, admirers were found, ready to encourage those
wretched competitions.
Now here is something far better, ye snobbish upholders of abstinence!
A trivial beastie, not celebrated by the newspapers, a grub born the
day before yesterday, takes a few mouthfuls; then, finding its victuals
too dry, it eats no more for four months or longer. And this is not the
result of sickly languor: the creature fasts in spite of the extreme
appetite of youth, when, more than ever, the stomach demands a copious
diet. The Rotifer, [46] which for a whole season lies lifeless and
desiccated in the mosses of its home, begins to whirl round again when
placed in a drop of water. The grub of the Attelabus, lying near to
death for four or five months, recovers its liveliness and eats like a
glutton if I moisten its bread for it. What can life be, capable of
such intermissions?