A large woodlouse (up to 15 mm), often slate-grey in colour, with pale areas giving the impression of three thin longitudinal stripes, but females may be attractively marked with orange mottling. The combination of five pairs of pleopodal lungs (see images) and two flagellal segments distinguish T. rathkii.
Distribution and Habitat
It has a ‘clumpy’ distribution across south-eastern England and into Wales (Jones, 2008), but is probably under-recorded. For example, it has been recently found by Jon Daws in Yorkshire (BMIG Newsletter 30, pg3). (NBN records on the west coast need to be verified). It favours sites with impeded drainage and is tolerant of flooding, making it a characteristic woodlouse of riverside meadows. It also inhabits poorly drained scrub, eroding ‘soft’ cliffs, gravel pits, churchyards, etc.
It occurs under stones and dead wood, beneath bark on logs, amongst grass litter, within tussocks and amongst flood debris. When found it may be the dominant species, but often associated with other ‘large’ woodlice, such as Porcellio scaber and Oniscus asellus and Philoscia muscorum.
This summary is based on the detailed account in Gregory (2009).