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?
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