Trichoniscus pusillus Brandt, 1833

Common name

Common Pygmy Woodlouse


Trichoniscus pusillus form pusillus
Trichoniscus pusillus sensu stricto


GB IUCN status: Least Concern

ID Difficulty

4 (or 2 for for T. pusillus/provisorius species agg.)


This is a small purplish-reddish species with eyes composed of three ommatidia and a smooth body surface. All body pigments are retained in alcohol. Although identical in appearance to the closely related T. provisorius, this species is consistently larger with gravid females reaching 4.5 mm (gravid females of T. provisorius rarely exceed 3.5 mm in length).

The two species can be reliably separated by microscopic examination of the male first exopod ~ see image (right) and BMIG Newsletter 18, pg2. Unfortunately, T. pusillus is parthenogentic and males are rarely encountered. Thus, T. pusillus s.s. is relatively under-recorded. 

Keith Lugg
Bill Urwin
Steve Gregory
Keith Lugg
Warren Maguire
Nicola Garnham
Nicola Garnham
Warren Maguire

Distribution and Habitat

This species is very common throughout Britain and Ireland and occupies a very broad habitat niche.  Unfortunately, most records are not differentiated between the two species (simply given as T. pusillus agg.).

There is considerable overlap with T. provisorius, but T. pusillus appears to be better suited to cooler, damper habitats.  It is usually found close to the soil surface, typically on the underside of stones and dead wood or amongst leaf-litter and moss.

This summary is based on the detailed account in Gregory (2009).



Gregory, S. (2009) Distinguishing species within the Trichoniscus pusillus species aggregate, BMIG Newsletter 18: pg 2.

Gregory, S. (2009) Woodlice and Waterlice (Isopoda: Oniscidea & Asellota) in Britain and Ireland.  Field Studies Council/Centre for Ecology & Hydrology.



BRC Code