Social Life in the Insect World | Page 8

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?
Larvæ 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 larvæ 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