{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 of the
ground without being torn into pieces. {11} During the day they
remain in their burrows, except at the pairing season, when those
which inhabit adjoining burrows expose the greater part of their
bodies for an hour or two in the early morning. Sick individuals,
which are generally affected by the parasitic larvae of a fly, must
also be excepted, as they wander about during the day and die on
the surface. After heavy rain succeeding dry weather, an
astonishing number of dead worms may sometimes be seen lying on the
ground. Mr. Galton informs me that on one such occasion (March,
1881), the dead worms averaged one for every two and a half paces
in length on a walk in Hyde Park, four paces in width. He counted
no less than 45 dead worms in one place in a length of sixteen
paces. From the facts above given, it is not probable that these
worms could have been drowned, and if they had been drowned they
would have perished in their burrows. I believe that they were
already sick, and that their deaths were merely hastened by the
ground being flooded.

It has often been said that under ordinary circumstances healthy
worms never, or very rarely, completely leave their burrows at
night; but this is an error, as White of Selborne long ago knew.
In the morning, after there has been heavy rain, the film of mud or