Social Life in the Insect World | Page 7

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 Petræa 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