[3] It is rare in the Mediterranean Basin, but is widespread in Northern and Western Europe, as far east as Ukraine, as well as in the Azores and Madeira; it has also been widely introduced in the Americas,[1] predominantly in Mexico and in the United States, east of the Mississippi River and west of the Rocky Mountains.

[2] The common woodlouse occurs in a wide range of habitats, including some with little available calcium.

[3] It is the only woodlouse regularly found on heather moors and blanket bogs, where it lives around items such as rotting fenceposts.

[3] The common woodlouse is one of the largest native woodlice in Britain, at up to 16 mm (0.63 in) long.

[4] Pale patches are often visible on the back of Oniscus asellus; these are areas that store calcium, which is then used to reinforce the exoskeleton after a moult.