Trichoniscus pygmaeus Sars, 1898

Common name

Least Pygmy Woodlouse


GB IUCN status: Least Concern

ID Difficulty



One of our smallest woodlice, reaching 2.5mm, and often confused with juveniles of other species. T. pygmaeus is usually pale pinkish-yellowish in colour, but characteristically the head appears noticably pale relative to any body pigmentation. As other Trichoniscus spp. the eye is composed of three black ommatidia and it has a smooth body surface. All pigments are retained in alcohol. 

In juvenile T. pusillus s.l. the head is speckled with pigment to match the body colour.  Trichoniscoides spp. and juvenile Androniscus dentiger have the body covered in tubercles and eyes comprising a single ommatidium.

J.P. Richards
Warren Maguire
Warren Maguire
J.P. Richards
Keith Lugg
Christian Owen
Nicola Garnham
Christian Owen
Steve Gregory

Distribution and Habitat

Although common throughout Britain and Ireland, it is under-recorded in many areas.  It occurs wherever there are suitable friable soil conditions, including semi-natural grasslands, woodlands and coastal (supralittoral) habitats, and synanthropic sites such as churchyards, disused quarries and railway cuttings. 

Searching the underside of large stones or dead wood partially embedded into soil is the simplest way to find this species.  It is typically associated with other soil-dwelling trichoniscids, including Androniscus dentiger, Haplophthalmus spp. and Trichoniscoides spp. 

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.



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