Confidence: It might be this.
Notes: Found in very wet woodland, sitting on a slug upon the base of a dead tree. Elytra seem darker brown than the reddish thorax and head. The size is good for the suggested species (4-6mm). Habitat, colouration and size are correct but I'm not sure there is enough of a flange/edge to the protonum of my beetle, when compared to the example given in the Ground Beetles of Ireland website.