What does wood contain that would attract woodlice?

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Hi -

It's not so much the wood as such, but the climate, and the shelter...

Woodlice (also called sowbugs, pillbugs, slaters etc) are crustaceans. Unlike most crustaceans they are not aquatic, but they are not all that brilliantly adapted to really dry conditions. For example, they breathe air through specially adapted gills, which must be kept damp to work, and in dry conditions they can lose a lot of water through them.

Like all small animals, they are very vulnerable to being eaten by slightly larger ones.

This means that during the daytime they stay in shelter which is damp (but not wet -- they don't like that either...). Under a bit of wood or stone, the soil moisture doesn't get blown away in the breeze or dried up in the sun, and so the humidity is usually high. It's also out of sight of birds and other biggish predators -- though smaller ones like carnivorous beetles and the fearsome woodlouse spider can still get them.

Woodlice eat mainly dead plant material, fungi and so on. They may eat rotting wood, but are probably more likely to come out from their shelter at night and search for food elsewhere.

There are many woodlouse species, and not all behave in the same way. The smaller ones (perhaps only 2 to 3 mm long) often live in spaces in soil or leaf litter. Some species live in the splash zone on the seashore -- we have one in Europe called the sea slater (Ligia oceanica) which can be 3 or more cm long. The "pillbugs" (Armadillidium and relatives - the ones which can roll fully into a ball), do live under stones and so on, but are also more ready to explore amongst vegetation in daylight than the three or four common flatter species. One very common species in the UK is a tiny white woodlouse found only in ants' nests -- it has the rather wonderful name of Platyarthrus hoffmanseggii.

Woodlice belong to a division of crustaceans called isopods ("feet all the same"). There are many freshwater and marine species in addition to the terrestrial ones, including for example the pond slater, Asellus.