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THE CIGALE LEAVES ITS BURROW




The first Cigales appear about the summer solstice. Along the beaten
paths, calcined by the sun, hardened by the passage of frequent feet, we
see little circular orifices almost large enough to admit the thumb.
These are the holes by which the larvae of the Cigale have come up from
the depths to undergo metamorphosis. We see them more or less
everywhere, except in fields where the soil has been disturbed by
ploughing. Their usual position is in the driest and hottest situations,
especially by the sides of roads or the borders of footpaths. Powerfully
equipped for the purpose, able at need to pierce the turf or sun-dried
clay, the larva, upon leaving the earth, seems to prefer the hardest
spots.

A garden alley, converted into a little Arabia Petraea by reflection from
a wall facing the south, abounds in such holes. During the last days of
June I have made an examination of these recently abandoned pits. The
soil is so compact that I needed a pick to tackle it.

The orifices are round, and close upon an inch in diameter. There is
absolutely no debris round them; no earth thrown up from within. This is
always the case; the holes of the Cigales are never surrounded by
dumping-heaps, as are the burrows of the Geotrupes, another notable
excavator. The way in which the work is done is responsible for this
difference. The dung-beetle works from without inwards; she begins to
dig at the mouth of the burrow, and afterwards re-ascends and
accumulates the excavated material on the surface. The larva of the
Cigale, on the contrary, works outward from within, upward from below;
it opens the door of exit at the last moment, so that it is not free for
the discharge of excavated material until the work is done. The first
enters and raises a little rubbish-heap at the threshold of her burrow;
the second emerges, and cannot, while working, pile up its rubbish on a
threshold which as yet has no existence.

The burrow of the Cigale descends about fifteen inches. It is
cylindrical, slightly twisted, according to the exigencies of the soil,
and always approaches the vertical, or the direction of the shortest
passage. It is perfectly free along its entire length. We shall search
in vain for the rubbish which such an excavation must apparently
produce; we shall find nothing of the sort. The burrow terminates in a
cul-de-sac, in a fairly roomy chamber with unbroken walls, which shows
not the least vestige of communication with any other burrow or
prolongation of the shaft.

Taking its length and diameter into account, we find the excavation has
a total volume of about twelve cubic inches. What becomes of the earth
which is removed?

Sunk in a very dry, crumbling soil, we should expect the shaft and the
chamber at the bottom to have soft, powdery walls, subject to petty
landslips, if no work were done but that of excavation. On the contrary,
the walls are neatly daubed, plastered with a sort of clay-like mortar.
They are not precisely smooth, indeed they are distinctly rough; but
their irregularities are covered with a layer of plaster, and the
crumbling material, soaked in some glutinous liquid and dried, is held
firmly in place.

The larva can climb up and down, ascend nearly to the surface, and go
down into its chamber of refuge, without bringing down, with his claws,
the continual falls of material which would block the burrow, make
ascent a matter of difficulty, and retreat impossible. The miner shores
up his galleries with uprights and cross-timbers; the builder of
underground railways supports the sides and roofs of his tunnels with a
lining of brick or masonry or segments of iron tube; the larva of the
Cigale, no less prudent an engineer, plasters the walls of its burrow
with cement, so that the passage is always free and ready for use.

If I surprise the creature just as it is emerging from the soil in order
to gain a neighbouring bough and there undergo transformation, I see it
immediately make a prudent retreat, descending to the bottom of its
burrow without the slightest difficulty--a proof that even when about to
be abandoned for ever the refuge is not encumbered with rubbish.

The ascending shaft is not a hurried piece of work, scamped by a
creature impatient to reach the sunlight. It is a true dwelling, in
which the larva may make a long stay. The plastered walls betray as
much. Such precautions would be useless in the case of a simple exit
abandoned as soon as made. We cannot doubt that the burrow is a kind of
meteorological observatory, and that its inhabitant takes note of the
weather without. Buried underground at a depth of twelve or fifteen
inches, the larva, when ripe for escape, could hardly judge whether the
meteorological conditions were favourable. The subterranean climate
varies too little, changes too slowly, and would not afford it the
precise information required for the most important action of its
life--the escape into the sunshine at the time of metamorphosis.

Patiently, for weeks, perhaps for months, it digs, clears, and
strengthens a vertical shaft, leaving only a layer of earth a finger's
breadth in thickness to isolate it from the outer world. At the bottom
it prepares a carefully built recess. This is its refuge, its place of
waiting, where it reposes in peace if its observations decide it to
postpone its final departure. At the least sign of fine weather it
climbs to the top of its burrow, sounds the outer world through the thin
layer of earth which covers the shaft, and informs itself of the
temperature and humidity of the outer air.

If things are not going well--if there are threats of a flood or the
dreaded _bise_--events of mortal gravity when the delicate insect issues
from its cerements--the prudent creature re-descends to the bottom of
its burrow for a longer wait. If, on the contrary, the state of the
atmosphere is favourable, the roof is broken through by a few strokes of
its claws, and the larva emerges from its tunnel.

Everything seems to prove that the burrow of the Cigale is a
waiting-room, a meteorological station, in which the larva makes a
prolonged stay; sometimes hoisting itself to the neighbourhood of the
surface in order to ascertain the external climate; sometimes retiring
to the depths the better to shelter itself. This explains the chamber
at the base of the shaft, and the necessity of a cement to hold the
walls together, for otherwise the creature's continual comings and
goings would result in a landslip.

A matter less easy of explanation is the complete disappearance of the
material which originally filled the excavated space. Where are the
twelve cubic inches of earth that represent the average volume of the
original contents of the shaft? There is not a trace of this material
outside, nor inside either. And how, in a soil as dry as a cinder, is
the plaster made with which the walls are covered?

Larvae which burrow in wood, such as those of Capricornis and Buprestes,
will apparently answer our first question. They make their way through
the substance of a tree-trunk, boring their galleries by the simple
method of eating the material in front of them. Detached by their
mandibles, fragment by fragment, the material is digested. It passes
from end to end through the body of the pioneer, yields during its
passage its meagre nutritive principles, and accumulates behind it,
obstructing the passage, by which the larva will never return. The work
of extreme division, effected partly by the mandibles and partly by the
stomach, makes the digested material more compact than the intact wood,
from which it follows that there is always a little free space at the
head of the gallery, in which the caterpillar works and lives; it is not
of any great length, but just suffices for the movements of the
prisoner.

Must not the larva of the Cigale bore its passage in some such fashion?
I do not mean that the results of excavation pass through its body--for
earth, even the softest mould, could form no possible part of its diet.
But is not the material detached simply thrust back behind the excavator
as the work progresses?

The Cigale passes four years under ground. This long life is not spent,
of course, at the bottom of the well I have just described; that is
merely a resting-place preparatory to its appearance on the face of the
earth. The larva comes from elsewhere; doubtless from a considerable
distance. It is a vagabond, roaming from one root to another and
implanting its rostrum. When it moves, either to flee from the upper
layers of the soil, which in winter become too cold, or to install
itself upon a more juicy root, it makes a road by rejecting behind it
the material broken up by the teeth of its picks. That this is its
method is incontestable.

As with the larvae of Capricornis and Buprestes, it is enough for the
traveller to have around it the small amount of free space necessitated
by its movements. Moist, soft, and easily compressible soil is to the
larva of the Cigale what digested wood-pulp is to the others. It is
compressed without difficulty, and so leaves a vacant space.

The difficulty is that sometimes the burrow of exit from the
waiting-place is driven through a very arid soil, which is extremely
refractory to compression so long as it retains its aridity. That the
larva, when commencing the excavation of its burrow, has already thrust
part of the detached material into a previously made gallery, now filled
up and disappeared, is probable enough, although nothing in the actual
condition of things goes to support the theory; but if we consider the
capacity of the shaft and the extreme difficulty of making room for such
a volume of debris, we feel dubious once more; for to hide such a
quantity of earth a considerable empty space would be necessary, which
could only be obtained by the disposal of more debris. Thus we are
caught in a vicious circle. The mere packing of the powdered earth
rejected behind the excavator would not account for so large a void. The
Cigale must have a special method of disposing of the waste earth. Let
us see if we can discover the secret.

Let us examine a larva at the moment of emerging from the soil. It is
almost always more or less smeared with mud, sometimes dried, sometimes
moist. The implements of excavation, the claws of the fore-feet, have
their points covered by little globules of mortar; the others bear
leggings of mud; the back is spotted with clay. One is reminded of a
scavenger who has been scooping up mud all day. This condition is the
more striking in that the insect comes from an absolutely dry soil. We
should expect to see it dusty; we find it muddy.

One more step, and the problem of the well is solved. I exhume a larva
which is working at its gallery of exit. Chance postpones this piece of
luck, which I cannot expect to achieve at once, since nothing on the
surface guides my search. But at last I am rewarded, and the larva is
just beginning its excavation. An inch of tunnel, free of all waste or
rubbish, and at the bottom the chamber, the place of rest; so far has
the work proceeded. And the worker--in what condition is it? Let us see.

The larva is much paler in colour than those which I have caught as they
emerged. The large eyes in particular are whitish, cloudy, blurred, and
apparently blind. What would be the use of sight underground? The eyes
of the larvae leaving their burrows are black and shining, and evidently
capable of sight. When it issues into the sunlight the future Cigale
must find, often at some distance from its burrow, a suitable twig from
which to hang during its metamorphosis, so that sight is obviously of
the greatest utility. The maturity of the eyes, attained during the time
of preparation before deliverance, proves that the larva, far from
boring its tunnel in haste, has spent a long time labouring at it.

What else do we notice? The blind, pale larva is far more voluminous
than in the mature state; it is swollen with liquid as though it had
dropsy. Taken in the fingers, a limpid serum oozes from the hinder part
of the body, which moistens the whole surface. Is this fluid, evacuated
by the intestine, a product of urinary secretion--simply the contents of
a stomach nourished entirely upon sap? I will not attempt to decide, but
for convenience will content myself with calling it urine.

Well, this fountain of urine is the key to the enigma. As it digs and
advances the larva waters the powdery debris and converts it into a
paste, which is immediately applied to the walls by the pressure of the
abdomen. Aridity is followed by plasticity. The mud thus obtained
penetrates the interstices of the rough soil; the more liquid portion
enters the substance of the soil by infiltration; the remainder becomes
tightly packed and fills up the inequalities of the walls. Thus the
insect obtains an empty tunnel, with no loose waste, as all the loosened
soil is utilised on the spot, converted into a mortar which is more
compact and homogeneous than the soil through which the shaft is
driven.

Thus the larva works in the midst of a coating of mud, which is the
cause of its dirtiness, so astonishing when we see it issue from an
excessively dry soil. The perfect insect, although henceforth liberated
from the work of a sapper and miner, does not entirely abandon the use
of urine as a weapon, employing it as a means of defence. Too closely
observed it throws a jet of liquid upon the importunate enemy and flies
away. In both its forms the Cigale, in spite of its dry temperament, is
a famous irrigator.

Dropsical as it is, the larva cannot contain sufficient liquid to
moisten and convert into easily compressible mud the long column of
earth which must be removed from the burrow. The reservoir becomes
exhausted, and the provision must be renewed. Where, and how? I think I
can answer the question.

The few burrows uncovered along their entirety, with the meticulous care
such a task demands, have revealed at the bottom, encrusted in the wall
of the terminal chamber, a living root, sometimes of the thickness of a
pencil, sometimes no bigger than a straw. The visible portion of this
root is only a fraction of an inch in length; the rest is hidden by the
surrounding earth. Is the presence of this source of sap fortuitous? Or
is it the result of deliberate choice on the part of the larva? I
incline towards the second alternative, so repeatedly was the presence
of a root verified, at least when my search was skilfully conducted.

Yes, the Cigale, digging its chamber, the nucleus of the future shaft,
seeks out the immediate neighbourhood of a small living root; it lays
bare a certain portion, which forms part of the wall, without
projecting. This living spot in the wall is the fountain where the
supply of moisture is renewed. When its reservoir is exhausted by the
conversion of dry dust into mud the miner descends to its chamber,
thrusts its proboscis into the root, and drinks deep from the vat built
into the wall. Its organs well filled, it re-ascends. It resumes work,
damping the hard soil the better to remove it with its talons, reducing
the debris to mud, in order to pack it tightly around it and obtain a
free passage. In this manner the shaft is driven upwards; logic and the
facts of the case, in the absence of direct observation, justify the
assertion.

If the root were to fail, and the reservoir of the intestine were
exhausted, what would happen? The following experiment will inform us: a
larva is caught as it leaves the earth. I place it at the bottom of a
test-tube, and cover it with a column of dry earth, which is rather
lightly packed. This column is about six inches in height. The larva has
just left an excavation three times as deep, made in soil of the same
kind, but offering a far greater resistance. Buried under this short
column of powdery earth, will it be able to gain the surface? If its
strength hold out the issue should be certain; having but lately made
its way through the hard earth, this obstacle should be easily removed.

But I am not so sure. In removing the stopper which divided it from the
outside world, the larva has expended its final store of liquid. The
cistern is dry, and in default of a living root there is no means of
replenishing it. My suspicions are well founded. For three days the
prisoner struggles desperately, but cannot ascend by so much as an inch.
It is impossible to fix the material removed in the absence of
moisture; as soon as it is thrust aside it slips back again. The labour
has no visible result; it is a labour of Sisyphus, always to be
commenced anew. On the fourth day the creature succumbs.

With the intestines full the result is very different.

I make the same experiment with an insect which is only beginning its
work of liberation. It is swollen with fluid, which oozes from it and
moistens the whole body. Its task is easy; the overlying earth offers
little resistance. A small quantity of liquid from the intestines
converts it into mud; forms a sticky paste which can be thrust aside
with the assurance that it will remain where it is placed. The shaft is
gradually opened; very unevenly, to be sure, and it is almost choked up
behind the insect as it climbs upwards. It seems as though the creature
recognises the impossibility of renewing its store of liquid, and so
economises the little it possesses, using only just so much as is
necessary in order to escape as quickly as possible from surroundings
which are strange to its inherited instincts. This parsimony is so well
judged that the insect gains the surface at the end of twelve days.

The gate of issue is opened and left gaping, like a hole made with an
augur. For some little time the larva wanders about the neighbourhood of
its burrow, seeking an eyrie on some low-growing bush or tuft of thyme,
on a stem of grass or grain, or the twig of a shrub. Once found, it
climbs and firmly clasps its support, the head upwards, while the talons
of the fore feet close with an unyielding grip. The other claws, if the
direction of the twig is convenient, assist in supporting it; otherwise
the claws of the two fore legs will suffice. There follows a moment of
repose, while the supporting limbs stiffen in an unbreakable hold. Then
the thorax splits along the back, and through the fissure the insect
slowly emerges. The whole process lasts perhaps half an hour.

There is the adult insect, freed of its mask, and how different from
what it was but how! The wings are heavy, moist, transparent, with
nervures of a tender green. The thorax is barely clouded with brown. All
the rest of the body is a pale green, whitish in places. Heat and a
prolonged air-bath are necessary to harden and colour the fragile
creature. Some two hours pass without any perceptible change. Hanging to
its deserted shell by the two fore limbs, the Cigale sways to the least
breath of air, still feeble and still green. Finally, the brown colour
appears and rapidly covers the whole body; the change of colour is
completed in half an hour. Fastening upon its chosen twig at nine
o'clock in the morning, the Cigale flies away under my eyes at half-past
twelve.

The empty shell remains, intact except for the fissure in the back;
clasping the twig so firmly that the winds of autumn do not always
succeed in detaching it. For some months yet and even during the winter
you will often find these forsaken skins hanging from the twigs in the
precise attitude assumed by the larva at the moment of metamorphosis.
They are of a horny texture, not unlike dry parchment, and do not
readily decay.

I could gather some wonderful information regarding the Cigale were I to
listen to all that my neighbours, the peasants, tell me. I will give one
instance of rustic natural history.



Are you afflicted with any kidney trouble, or are you swollen with
dropsy, or have you need of some powerful diuretic? The village
pharmacopoeia is unanimous in recommending the Cigale as a sovereign
remedy. The insects in the adult form are collected in summer. They are
strung into necklaces which are dried in the sun and carefully preserved
in some cupboard or drawer. A good housewife would consider it imprudent
to allow July to pass without threading a few of these insects.

Do you suffer from any nephritic irritation or from stricture? Drink an
infusion of Cigales. Nothing, they say, is more effectual. I must take
this opportunity of thanking the good soul who once upon a time, so I
was afterwards informed, made me drink such a concoction unawares for
the cure of some such trouble; but I still remain incredulous. I have
been greatly struck by the fact that the ancient physician of Anazarbus
used to recommend the same remedy. Dioscorides tells us: _Cicadae, quae
inassatae manduntur, vesicae doloribus prosunt_. Since the distant days
of this patriarch of _materia medica_ the Provencal peasant has retained
his faith in the remedy revealed to him by the Greeks, who came from
Phocaea with the olive, the fig, and the vine. Only one thing is changed:
Dioscorides advises us to eat the Cigales roasted, but now they are
boiled, and the decoction is administered as medicine. The explanation
which is given of the diuretic properties of the insect is a marvel of
ingenuousness. The Cigale, as every one knows who has tried to catch it,
throws a jet of liquid excrement in one's face as it flies away. It
therefore endows us with its faculties of evacuation. Thus Dioscorides
and his contemporaries must have reasoned; so reasons the peasant of
Provence to-day.

What would you say, worthy neighbours, if you knew of the virtues of the
larva, which is able to mix sufficient mortar with its urine to build a
meteorological station and a shaft connecting with the outer world? Your
powers should equal those of Rabelais' Gargantua, who, seated upon the
towers of Notre Dame, drowned so many thousands of the inquisitive
Parisians.





Next: THE SONG OF THE CIGALE

Previous: THE FABLE OF THE CIGALE AND THE ANT



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