Proasellus meridianus (Racovitza, 1919)

Common name

One-spotted Waterlouse, One-spotted Water-slater


Asellus meridianus Racovitza, 1919


GB IUCN status: Least Concern

ID Difficulty


Proasellus meridianus can usually by distinguished from Asellus aquaticus by the continuous pale band along the posterior margin of the head.  However, care is needed since in some specimens the dark gut can be seen through the pale head giving an impression of a pigmented patch. Consequently the the two species are frequently confused. The shape of the male first pereopod is diagnostic.

Keith Lugg
Warren Maguire
Warren Maguire
Warren Maguire
Warren Maguire
Warren Maguire


P. meridianus occurs throughout Britain (but under-recorded in Wales and Scotland). In many areas it is much less frequently recorded than A. aquaticus.  There are very few, mostly old, Irish records, again perhaps reflecting under-recording.  


Although found in similar places to A. aquaticus, among water plants, under stones and submerged bits of dead wood, etc, it is rarely found in garden ponds and is much less tolerant of pollution.

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.

BRC code