Patrobus septentrionis Dejean, 1828
This cold-adapted species is native to the Holarctic region, it is widely distributed across the northern United States and Canada and locally common in northern Europe, extending north to Iceland and the far north of Fennoscandia where it occurs above the tree-line, further south it extends sporadically to northern Italy and Ukraine but most populations are relicts and confined to boreo-alpine regions. Here it is locally common across northern Scotland, the Western Isles and Shetland, more local and rare in the south of Scotland, northern England and the north of Wales and there is an old record from southwest Ireland. Adults are active over a short season, from May until September, occurring mostly in damp and well-vegetated habitats, often beside streams and tarns etc. but also in marshes and wet meadows and among sedges in permanently damp woodland, they are active by day and night and on the continent have been recorded hunting and scavenging dead insects beside fresh snow falls above the tree-line. They tend to be common where they occur and are sometimes found in company with Patrobus assimilis (Chaud.), Pelophila borealis (Pk.) and other upland carabids. It is likely that larvae overwinter and pupate in late spring/early summer as freshly eclosed adults occur between June and August.
7.4-10.0mm. Body black or very dark brown but the elytra is often reddish with the suture darker, appendages a little paler brown, more slender and with longer elytra than our other UK species but readily distinguished by the fully-developed wings. Head with large convex eyes and short temples (about half the length of the eyes) strongly contracted to a short neck, vertex smooth but for a transverse band of punctures behind the eyes, frontal furrows converging anteriorly, the area between these and the lateral margin only slightly broadened anteriorly (intermediate between P. assimilis and P. atrorufus), Antennae long and slender with the third segment longer than the first. Pronotum transverse, about 1.3X wider than long, widest in front of the middle and sinuate to almost perpendicular posterior angles, transverse impression behind the anterior margin deep and coarsely punctured, the area between this and the margin distinctly raised, basal fovea wide and punctured, delimited externally by a keel, median longitudinal impression complete and slightly broadened towards the base. Elytra long and only weakly curved laterally (when compared with our other Patrobus species), with prominent rounded shoulders and weakly-impressed and punctured striae, basal margin not continued past the shoulder, interstices flat or weakly convex, the third with three or four setiferous punctures beside the fourth stria. Basal segments of pro-tarsi dilated in the male.