CRUSTACEA > MALACOSTRACA > ISOPODA > Oniscidea > Crinocheta > Oniscidae

Oniscus asellus is the most abundant and frequently recorded woodlouse in Britain. It's also one of the largest species with mature individuals reaching up to 18mm in length. The body can be somewhat variable in both shape and colour, but is noticeably flattened and often quite broad. The outline is continuous and the colour normally grey-brown with a shiny texture, together with irregular lighter markings and a row of yellowish patches along the flanks. Yellow and orange forms can occur, but they're not common. The eyes are composed of numerous ocelli, and the antennal flagellum each have three distinct segments. This woodlouse has a very defined elongated telson, but lacks the pleopodal lungs that can be seen on the underside of species within the Porcellionidae and Armadillidiidae families.

There are few habitats where Oniscus asellus does not occur, but it is perhaps most frequently found in damper environments typical of those that occur in many woodlands, parks and gardens, but also along hedgerows, on waste ground or in damp meadows. The species is common and widespread across the country, but with a genetically distinct subspecies ssp.occidentalis in the extreme southwest, which is a bit smaller, higher backed and more brightly coloured, and prefers rural areas, whereas the nominate species readily colonises synanthropic sites.

The first photo below from the South Oakley Inclosure near Burley in the New Forest is the scarce 'orange form' of the species.