Ground Beetles of Ireland

Trechus rivularis

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Trechus rivularis
© Roy Anderson
Trechus rivularis
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(Maps updated 30th November 2009)

Trechus rivularis (Gyllenhal, 1810)

Description: A small (3.5-4mm) brownish ground beetle living in dense vegetation on montane peatlands and wet acid grasslands. Only in the north and east so far but difficult to detect and probably overlooked elsewhere.

World Distribution: This species has an interesting European distribution which is basically northerly but restricted, ranging from Fennoscandia through Denmark and Russia to the British Isles, Belgium, parts of Germany and into Slovakia. We classify this as European Wide-Boreal (33), a category apparently not encountered in the British flora (Preston & Hill, 1997), or possibly European Boreo-temperate.

Irish Status: Historically, restricted to the East Anglian fens and Yorkshire within the British Isles, but now known to have a much wider range including northern England, Scotland and northern parts of Ireland (Luff, 1998). It has been found only by pitfall trap on hill peat in Cos Antrim, Fermanagh and Tyrone within Ireland. Easily overlooked but the distinctive pronotal shape will distinguish it from the similar-sized T. obtusus.

Ecology: Originally thought to be restricted to lowland fen districts, it now transpires that the species is widely, but very thinly spread on upland ombrotrophic mires in the north and west of the British Isles. Added to the Irish List by Day (1987) from pitfall traps on upland raised bog at Slieveanorra, north Antrim. Anderson & Meharg (1989) and Anderson & Cameron (1992) subsequently provided records for south Antrim, Tyrone and Fermanagh. It has been reported from a variety of upland mire types, but is usually rare and caught singly by pitfall trapping.