One-spotted Waterlouse - Proasellus meridianus

    Alt Name
    Asellus meridianus
    One-spotted Water-slater

    This species can usually by distinguished from Asellus aquaticus by the continuous pale band along the posterior margin of the head.  However, care is needed since the two species are frequently confused. The shape of the male first pereopod is diagnostic.

    Similar Species

    Asellus aquaticus is very similar but this species has two pale spots on its head, rather than the single bar of Proasellus meridianus.

    Identification difficulty
    ID guidance
    • single pale bar on the top of the head
    Recording advice

    Attach an image showing the pale bar on the head or add a comment describing how you identified the species.


    Often found in stagnant water as they can tolerate low oxygen levels.  They do not swim well but tend to crawl around weed and mud.

    When to see it

    All year round.

    Life History

    They are detritus feeders, eating decaying organic matter.  The species breeds throughout the vegetation period, most frequently in spring. Females carry eggs in brood pouches underneath their body.

    UK Status

    Widespread and fairly frequent in Britain.

    VC55 Status

    Status in Leicestershire and Rutland not known.

    Leicestershire & Rutland Map

    MAP KEY:

    Yellow squares = NBN records (all known data)
    Coloured circles = NatureSpot records: 2020+ | 2015-2019 | pre-2015

    UK Map