110
THE ESSEX NATURALIST.
in a heap of old "clinkers." I have twice found them in the
vicinity of the nests of Formica rufa.8 They seem to prefer
vertical surfaces where moisture clings yet cannot collect and
become excessive. Their presence beneath the bark of living
trees does not appear to interfere with growth, since the wood-
lice do not penetrate into the soft, living cambial tissues. They
favour no particular genus of tree, but willows very often harbour
them, since the bark of these trees is loose, affording ample
shelter for the creatures, and also these trees in particular grow
in damp situations. I have never found the woodlice in coni-
ferous trees. Albino specimens are not altogether rare ; one I
succeeded in rearing from a few weeks old up to the age of two
years. Found all the year round, but rarer in winter. No sexual
difference in colouration, but the males are slightly more slender,
with longer uropods.
Oniscus asellus. The commonest of all woodlice, found
almost everywhere where damp conditions prevail, particularly
beneath damp stones half buried in the earth, amongst old plant
pots, and beneath the loose bark on the lower side of a fallen
tree trunk which is in the early stages of decay, or an old tree
stump. They prefer rather moister situations than P. scaber
and may often be found with the latter in the same tree but nearer
the ground, where the wood is old and rotting. Occasionally
found in damp cellars where there are rotting carrots, potatoes,
etc., but not generally so common in this situation as P. scaber.
Found almost all the year round, but rarer in winter. No sexual
difference in colouration or in size.
Philoscia muscorum. Fairly common in moist, shady
situations in woodlands, particularly amongst the roots of
grasses growing beneath low bushes, brambles, etc., and at the
base of tree trunks, where the soil receives the drippings from the
trees and is shaded from the sun. They are decidedly more local
and restricted in their distribution than the two former species,
and appear to be present only in woodlands. In the winter and
early spring, when the ground is bare and the grass shoots small,
they are exceedingly difficult to find, and are usually hiding
amongst the wet masses of fallen leaves, together with T.
8 R. S. Bagnall (1913) also noticed their occurrence in the nests of wood ants. He regards
them as a special variety—P. Scaber var. Darwiniana.