Work of this kind is usually performed during the night; but I have
occasionally known objects to be drawn into the burrows during the day.
What advantage the worms derive from plugging up the mouths of their
burrows with leaves, &c., or from piling stones over them, is doubtful.
They do not act in this manner at the times when they eject much earth
from their burrows; for their castings then serve to cover the mouths.
When gardeners wish to kill worms on a lawn, it is necessary first to
brush or rake away the castings from the surface, in order that the
lime-water may enter the burrows. {59a} It might be inferred from this
fact that the mouths are plugged up with leaves, &c., to prevent the
entrance of water during heavy rain; but it may be urged against this
view that a few, loose, well-rounded stones are ill-adapted to keep out
water. I have moreover seen many burrows in the perpendicularly cut
turf-edgings to gravel-walks, into which water could hardly flow, as well
plugged as burrows on a level surface. It is not probable that the plugs
or piles of stones serve to conceal the burrows from scolopendras, which,
according to Hoffmeister, {59b} are the bitterest enemies of worms, or
from the larger species of Carabus and Staphylinus which attack them
ferociously, for these animals are nocturnal, and the burrows are opened
at night. May not worms when the mouth of the burrow is protected be
able to remain with safety with their heads close to it, which we know
that they like to do, but which costs so many of them their lives? Or
may not the plugs check the free ingress of the lowest stratum of air,
when chilled by radiation at night, from the surrounding ground and
herbage? I am inclined to believe in this latter view: firstly, because
when worms were kept in pots in a room with a fire, in which case cold
air could not enter the burrows, they plugged them up in a slovenly
manner; and secondarily, because they often coat the upper part of their
burrows with leaves, apparently to prevent their bodies from coming into
close contact with the cold damp earth. Mr. E. Parfitt has suggested to
me that the mouths of the burrows are closed in order that the air within
them may be kept thoroughly damp, and this seems the most probable
explanation of the habit. But the plugging-up process may serve for all
the above purposes.
Whatever the motive may be, it appears that worms much dislike leaving
the mouths of their burrows open. Nevertheless they will reopen them at
night, whether or not they can afterwards close them. Numerous open
burrows may be seen on recently-dug ground, for in this case the worms
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