This large pill-woodlouse (to 18 mm) is often uniform slate grey, but can be highly variable in colour and mottled forms are often seen. However, it lacks the dark patch on the 7th epimera, and the well developed ornate mottling, characteristic of A. pulchellum or A. pictum. See Gregory & Richards (2008) for details of the identification of the three species.
In south Wales and southern England it can be confused with A. depressum (which can be locally common in gardens, etc).
Distribution and Habitat
It is locally abundant in south-eastern England and is common in most habitats. It becomes much scarcer further north and restricted to lowland sites with calcareous soils and high levels of insolation. Scottish sites are mostly coastal, where it occurs as far north as Aberdeenshire (Davidson, 2010). [The record from the northern Scottish coast is erroneus.]
It is most easily found under stones and dead wood, but also amongst grass litter, within tussocks, etc.
This summary is based on the detailed account in Gregory (2009).
Gregory, S. (2009) Woodlice and Waterlice (Isopoda: Oniscidea & Asellota) in Britain and Ireland. Field Studies Council/Centre for Ecology & Hydrology.
Gregory, S. & Richards, P. (2008) Comparison of three often mis-identified species of pill-woodlouse Armadillidium (Isopoda: Oniscidea). Bulletin of the British Myriapod & Isopod Group, 23: 9-12.