Woodlice (known locally under many names; see below) are terrestrial crustaceans with a rigid, segmented, calcareous exoskeleton and fourteen jointed limbs. They form the suborder Oniscidea within the order Isopoda, with over 3000 known species.
Woodlice need moisture because they breathe through gills, called pseudotrachea, and so are usually found in damp, dark places, such as under rocks and logs. They are usually nocturnal and are detritivores, feeding mostly on dead plant matter. They should be considered beneficial garden organisms as they recycle nutrients back into the soil. In artificial environments such as greenhouses where it can be very moist, woodlice may become abundant and damage young plants.
Common names for woodlice vary throughout the English-speaking world. They include roly-poly, pill bug (usually applied only to the genus Armadillidium), sow bug, doodle bug, carpenter (Newfoundland), woodbug, potato bug, armadillo bug, slater, ball bug, bowling ball bug, chuggy pig, hardy back, butcher boy, daddy gramfer / daddy gampfer (West Country), Granny Grey (South Wales), cheesybug (Kent), and cheeselog.