Woodlice are the most species-rich group of terrestrial crustaceans. Of the 4,000 described species found worldwide, 35 species in 10 families are native to the British Isles. One of these species, Acaeroplastes melanurus, had been considered extinct in the British Isles but was rediscovered in 2002 at its only site (Howth, County Dublin, Ireland), and a further ten species have become naturalised in greenhouses, presumably transported with exotic plants. Five species are especially common throughout the British Isles, and are known as the "famous five species". They are Oniscus asellus (the common shiny woodlouse), Porcellio scaber (the common rough woodlouse), Philoscia muscorum (the common striped woodlouse), Trichoniscus pusillus (the common pygmy woodlouse) and Armadillidium vulgare (the common pill bug). One species, Metatrichoniscoides celticus, is endemic to Glamorgan, and is listed as a vulnerable species in the IUCN Red List.

Armadillidae

Armadillidiidae

"Pill bugs" of the family Armadillidiidae are often confused with pill millipedes such as Glomeris marginata, which is also widespread and common in Britain and Ireland, but pill millipedes have two pairs of legs per body segment, while woodlice have only seven pairs of legs. Six certainly native species occur in the British Isles; some doubt exists as to the status of Eluma caelatum.

Cylisticidae

Halophilosciidae

Haplophilosciidae is a family of woodlice lacking pleopodal lungs. Its members are therefore restricted to coastal habitats.

Ligiidae

Oniscidae

Philosciidae

Porcellionidae

Platyarthridae

Styloniscidae

Trachelipodidae

Trichoniscidae