Archaeologists ought to be grateful to worms, as they protect and
preserve for an indefinitely long period every object, not liable
to decay, which is dropped on the surface of the land, by burying
it beneath their castings.- Thus, also, many elegant and curious
tesselated pavements and other ancient remains have been preserved;
though no doubt the worms have in these cases been largely aided by
earth washed and blown from the adjoining land, especially when
cultivated.- The old tesselated pavements have, however, often
suffered by having subsided unequally from being unequally
undermined by the worms.- Even old massive walls may be undermined
and subside; and no building is in this respect safe, unless the
foundations lie 6 or 7 feet beneath the surface, at a depth at
which worms cannot work.- It is probable that many monoliths and
some old walls have fallen down from having been undermined by
worms.
Worms prepare the ground {82} in an excellent manner for the growth
of fibrous-rooted plants and for seedlings of all kinds.- They
periodically expose the mould to the air, and sift it so that no
stones larger than the particles which they can swallow are left in
it.- They mingle the whole intimately together, like a gardener who
prepares fine soil for his choicest plants.- In this state it is
well fitted to retain moisture and to absorb all soluble
substances, as well as for the process of nitrification.- The bones
of dead animals, the harder parts of insects, the shells of land-
molluscs, leaves, twigs, &c., are before long all buried beneath
the accumulated castings of worms, and are thus brought in a more
or less decayed state within reach of the roots of plants.- Worms
likewise drag an infinite number of dead leaves and other parts of
plants into their burrows, partly for the sake of plugging them up
and partly as food.
The leaves which are dragged into the burrows as food, after being
torn into the finest shreds, partially digested, and saturated with
the intestinal and urinary secretions, are commingled with much
earth.- This earth forms the dark coloured, rich humus which almost
everywhere covers the surface of the land with a fairly well-
defined layer or mantle.- Hensen {83} placed two worms in a vessel
18 inches in diameter, which was filled with sand, on which fallen
leaves were strewed; and these were soon dragged into their burrows
to a depth of 3 inches.- After about 6 weeks an almost uniform
layer of sand, a centimeter (0.4 inch) in thickness, was converted
into humus by having passed through the alimentary canals of these
two worms.- It is believed by some persons that worm-burrows, which
often penetrate the ground almost perpendicularly to a depth of 5
or 6 feet, materially aid in its drainage; notwithstanding that the
viscid castings piled over the mouths of the burrows prevent or
check the rain-water directly entering them.- They allow the air to
penetrate deeply into the ground.- They also greatly facilitate the
downward passage of roots of moderate size; and these will be
nourished by the humus with which the burrows are lined.- Many
seeds owe their germination to having been covered by castings; and
others buried to a considerable depth beneath accumulated castings
lie dormant, until at some future time they are accidentally
uncovered and germinate.