Asellus aquaticus (Linnaeus, 1758)

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Common name

Two-spotted Waterlouse, Two-spotted Water-slater

Status:

GB IUCN status: Least Concern

ID Difficulty

3

Identification

Waterlice (Asellidae) are distinguished from the terrestrial woodlice by their plate-like pleotelson, consisting of four pleonites and the telson fused together.

Asellus aquaticus can usually be distinguished from the frequent Proasellus meridianus by the pattern of pigmentation of the head, with two pale spots at the back separated by a central dark pigmented area. However, head pigmentation can vary and the two species are frequently confused.  The situation is further complicated by the recent discovery of the introduced Proasellus coxalis in England. The shape of the male first pereopod (leg) is diagnostic.

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

Distribution

Asellus aquaticus is abundant throughout Britain (but under-recorded in Wales and Scotland) and probably across Ireland (where is seems to be badly under-recorded). 

Habitat

It occurs in a wide variety of water-bodies, including small urban garden ponds, ditches, lakes, canals and rivers.

Specimens can be found among water plants, under stones and submerged bits of dead wood, among the roots of riparian trees and on the stonework of bridges.  It is tolerant of organically polluted waters, high salinities, low pH and high metal concentrations.

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

References

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

Links

World List of Marine, Freshwater and Terrestrial Isopod Crustaceans: https://www.marinespecies.org/isopoda/aphia.php?p=taxdetails&id=264152

BRC code

91

idBmigTaxa

Cru_1100