Woodlice have an oval body and are between 12 and 15 mm long. They are typically grey, brown or black in colour. Their body is protected by a shell-like exoskeleton. They have seven pairs of legs.
The English-speaking world separates woodlice into two groups: sowbugs and pillbugs. Sowbugs possess two tail-like appendages at the tip of the abdomen. Pillbugs have no posterior appendages and can roll up into a tight ball when disturbed.