Trichoniscus pusillus sensu stricto
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, but since T. pusillus is parthenogentic males are rarely encountered. Thus, T. pusillus s.s. is relatively under-recorded.
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.