The Formation of Vegetable Mould Through the Action of Worms | Page 5

surface
in the form of castings. Hoffmeister says that the species in Germany
are not well known, but gives the same number as Eisen, together with
some strongly marked varieties. {8}
Earth-worms abound in England in many different stations. Their
castings may be seen in extraordinary numbers on commons and chalk-
downs, so as almost to cover the whole surface, where the soil is poor
and the grass short and thin. But they are almost or quite as numerous
in some of the London parks, where the grass grows well and the soil
appears rich. Even on the same field worms are much more frequent in
some places than in others, without any visible difference in the nature
of the soil. They abound in paved court- yards close to houses; and an
instance will be given in which they had burrowed through the floor of
a very damp cellar. I have seen worms in black peat in a boggy field;
but they are extremely rare, or quite absent in the drier, brown, fibrous
peat, which is so much valued by gardeners. On dry, sandy or gravelly
tracks, where heath with some gorse, ferns, coarse grass, moss and
lichens alone grow, hardly any worms can be found. But in many parts
of England, wherever a path crosses a heath, its surface becomes
covered with a fine short sward. Whether this change of vegetation is
due to the taller plants being killed by the occasional trampling of man
and animals, or to the soil being occasionally manured by the droppings
from animals, I do not know. {9} On such grassy paths worm- castings
may often be seen. On a heath in Surrey, which was carefully examined,
there were only a few castings on these paths, where they were much
inclined; but on the more level parts, where a bed of fine earth had been
washed down from the steeper parts and had accumulated to a thickness
of a few inches, worm-castings abounded. These spots seemed to be
overstocked with worms, so that they had been compelled to spread to
a distance of a few feet from the grassy paths, and here their castings
had been thrown up among the heath; but beyond this limit, not a single
casting could be found. A layer, though a thin one, of fine earth, which
probably long retains some moisture, is in all cases, as I believe,
necessary for their existence; and the mere compression of the soil
appears to be in some degree favourable to them, for they often abound
in old gravel walks, and in foot-paths across fields.

Beneath large trees few castings can be found during certain seasons of
the year, and this is apparently due to the moisture having been sucked
out of the ground by the innumerable roots of the trees; for such places
may be seen covered with castings after the heavy autumnal rains.
Although most coppices and woods support many worms, yet in a
forest of tall and ancient beech-trees in Knole Park, where the ground
beneath was bare of all vegetation, not a single casting could be found
over wide spaces, even during the autumn. Nevertheless, castings were
abundant on some grass- covered glades and indentations which
penetrated this forest. On the mountains of North Wales and on the
Alps, worms, as I have been informed, are in most places rare; and this
may perhaps be due to the close proximity of the subjacent rocks, into
which worms cannot burrow during the winter so as to escape being
frozen. Dr. McIntosh, however, found worm-castings at a height of
1500 feet on Schiehallion in Scotland. They are numerous on some
hills near Turin at from 2000 to 3000 feet above the sea, and at a great
altitude on the Nilgiri Mountains in South India and on the Himalaya.
Earth-worms must be considered as terrestrial animals, though they are
still in one sense semi-aquatic, like the other members of the great class
of annelids to which they belong. M. Perrier found that their exposure
to the dry air of a room for only a single night was fatal to them. On the
other hand he kept several large worms alive for nearly four months,
completely submerged in water. {10} During the summer when the
ground is dry, they penetrate to a considerable depth and cease to work,
as they do during the winter when the ground is frozen. Worms are
nocturnal in their habits, and at night may be seen crawling about in
large numbers, but usually with their tails still inserted in their burrows.
By the expansion of this part of their bodies, and with the help of the
short, slightly reflexed bristles, with which their bodies are armed, they
hold so fast that they can seldom be dragged out