The little creatures with grey or brownish armour-plating and seven pairs of legs are crustaceans – distant land-living relations of crabs and lobsters. There are several species of woodlice, but they rarely exceed 2cm/4⁄5in in length.
They thrive in damp places, and cannot survive for long in dry conditions. They are therefore mainly active at night, when they scavenge for decaying plant material, including rotten wood. Though they seldom damage living plants, they sometimes nibble seedlings, and occasionally enlarge holes in mature plants started by slugs.
Many gardeners destroy woodlice in the belief that they are harmful pests. They probably do more good than harm, however, because by eating decaying vegetation the return of minerals to the soil is speeded up.
Woodlice are only likely to be a problem where garden plants are situated near rubbish or compost heaps, and in a greenhouse. Control them by removing their staple diet and resting places, i.e. all loose wood and rotting vegetation, stored pots, etc.
Prepare traps by placing inverted flower pots filled with dead grass at various sites around the greenhouse.
Check daily and remove any woodlice found in them.
Remember: Bark mulches and similar materials can also provide woodlice with protection.