Patrobus atrorufus (Strøm, 1768)
This is the most common and widespread member of the genus, it occurs throughout northern and central Europe south to northern Italy, Bulgaria and Ukraine, extending east into western Siberia, and north into the UK and Fennoscandia except for the far north, in northern areas it occurs from lowland to mountain altitudes but in southern parts of the range it seems to prefer cooler areas and may be common on subalpine moors and woodland. Here it is locally common throughout mainland UK, it also occurs on Anglesey, Orkney and Shetland as well as various western Isles but seems to be absent from the Outer Hebrides, in Ireland it is very local and sporadic in the north. Typical habitats are damp deciduous woodland and parkland on heavy clay soil but they also occur on shaded river banks, agricultural land and other disturbed situations including domestic gardens. Adults are mostly nocturnal and may be found among litter and under logs and debris; they are active over a long season from February until November and may be found, though rarely, through the winter. Breeding occurs during August and September and larvae overwinter, completing their development in the spring, most adults die-off late in the year but a small proportion will survive until the following spring. Pupation occurs in the spring and new-generation adults appear in early summer, they are active for only a short while before entering into a summer diapause in the soil, re-emerging later in the summer to breed.
7.0-9.5mm. entirely dark brown, often with the elytral suture reddish and with paler appendages, superficially similar to some Pterostichus but distinguished by the strongly contracted temples and pubescent second antennomere. Body glabrous, head and pronotum with at most very fine transverse wrinkles. Head with large convex eyes and sharp, forwardly protruding mandibles, temples strongly contracted to a broad neck delimited by a transverse and strongly punctured furrow, vertex finely punctured, two supra-orbital punctured beside each eye and slightly converging frontal furrows; the area between these and the lateral margin becoming a little broader anteriorly. Antennae long and slender with the third segment distinctly longer than the first. Pronotum transverse, broadest in front of the middle and strongly narrowed behind, almost parallel-sided towards near perpendicular posterior angles, basal fovea broad and shallow, with scattered strong punctures and delimited externally by a strong longitudinal ridge, subapical transverse furrow with a single row of punctures. Elytra elongate and smoothly curved from rounded shoulders to a continuously-rounded apical margin, basal border not continued inside the shoulders, striae complete and punctured though progressively so towards the apex, interstices flat or only weakly convex, the third with three setiferous punctures beside the fourth stria. Hind wings always reduced, about half the elytral length. Male with basal pro-tarsal segments dilated.