Ocys harpaloides (Audinet-Serville, 1821)
Widespread and common throughout England and Wales and with scattered records in southern and central Scotland. A woodland species found under bark or either under logs or among moss or fungi growing among them. Around Watford it occurs in most habitats; through the winter in grass tussocks or among bark in parkland and woodland, even in the town centre, but in spring they are active everywhere e.g. among deep reed litter along the river Colne.In general they seem to prefer damp situations. A spring and early summer breeder. Usually found singly or in pairs but during spring 2005 was attracted in numbers (10-20) to UV in Whippendell wood. Immature adults have been found in the nest of a Jay (Lindroth, 1974)

4-6mm. Unmistakable. Entirely light brown with the head a little darker. Elytra almost black with a bluish hue and weak metallic lustre, side margin and suture often lighter. Striae punctate, very weakly so apically and fifth stria with a short deep impression where it joins the shoulder stria. A single large pore adjoins the third stria behind the middle. Sutural stria recurrent i.e. forms a broad U shape inside the elytral apex, a small but very distinct ridge lies outside the reflexed part, the whole detail being easy to see as the the other striae are very weak apically. Pronotum broadly cordiform with sharp hind angles and basal margin almost straight. Terminal segment of maxillary palpi very small, diagnostic of Bembidion in which this species was formerly included in the subgenera Ocys.

Description from 3 Watford specimens at X40