Adult:  20–30 mm

Identification marks

An adult common woodlouse (Oniscus asellus) is flat, dark brown, jointed crustacean. The larva is similar to the adult, but smaller in size. Wide, jointed shields on the back are characteristic to the isopoda. The common rough woodlouse (Porcellio scaber) can be told apart from the common woodlouse by the lumps on the back shields and the tip of its two-segment antennae.


Land-dwelling isopods are the only crustaceans that have adapted to living on land.


Even though they live on land, they use a set of gills to breathe, which is why they avoid dry places.

A common woodlouse prefers damp and shadowed places, such as rotten tree stumps and spots under thick, fallen branches and rocks. It usually moves around at nights, when the moisture level of the air is higher. Land-dwelling isopods feed on rotting plans and animal waste.

Isopods are also seen in greenhouses and gardens. They may end up indoors, especially in cellars, with soil, damp hay or root vegetables.


Isopods may sometimes cause damage by gnawing on root vegetables.

Prevention and extermination

Isopods are attracted to the damp undersides of sacks, for example, and are easy to clean away.