It is widespread in Europe, the British Isles and is found from southern Scandinavia to Ukraine and Greece.

[4] It has also spread to Washington and many states in New England, also the mid-Atlantic states of Pennsylvania and New Jersey, as well as Nova Scotia.

[4] P. muscorum may reach 11 millimetres (0.43 in) in length, with a shiny body which is mottled and greyish-brown in colour.

[3] The fast woodlouse is, as its name suggests, faster than other common species; its body is raised up off the ground rather more than the others and the head is always very dark in colour.

Twelve subspecies are recognised:[1]