Pterostichus gracilis (Dejean, 1828)
Present throughout most of the western Palaearctic region and extending east into Siberia, this species occurs sporadically throughout Europe from Portugal to Italy and northern Greece in the south and north to the UK, Denmark and the Baltic countries where it is rare in southern Finland and Sweden but absent from Norway. There are records from some of the larger Mediterranean islands but it is absent from North Africa. Across much of Europe it is very local and generally rare and there is evidence of a recent decline, especially in northern areas, although it remains locally common in parts of France and northern and eastern Germany. In the UK there seems to have been a general decline; it remains widespread but is now very local and generally scarce across southern and central England and Wales, it was formerly widespread though very local in Ireland but there are very few modern records. This is a lowland species (recorded up to 750m. in Switzerland) of well-vegetated wetlands, typically occurring on heavy soils beside standing and slow-moving water but also on seasonally inundated floodplain grassland and in damp woodland, occasionally some distance from water. Adults are present year-round; they overwinter away from water, under bark, in dead wood or among litter at the base of trees although they are often active in all but the coldest periods, and are otherwise active from early spring until late autumn, peaking in abundance during May and June and again, although much less so, in late summer or autumn. Reproduction occurs from early spring and larvae develop through the summer to produce new-generation adults in the autumn. Wings and flight muscles are usually well developed and flight has been observed on the continent. Adults are predatory and nocturnal, they may be found by searching or pitfall trapping among vegetation but specimens will need to be taken for examination as other similar and common species occur in the same habitats.
8.5-9.5 mm. Entirely shiny black or sometimes with slightly paler appendages. Head smooth between convex and prominent convex eyes, frontal furrows usually only weakly impressed, frons with two setiferous punctured beside each eye. Antennae densely pubescent from the fourth segment. Pronotum transverse, broadest slightly in front of the middle and sinuate before sharp or finely toothed posterior angles, basal fovea punctured and rather flat; the inner extending at most only slightly further forward than the outer, and the outer keeled externally. Elytra long and almost parallel-sided from rounded and finely-toothed shoulders to a smooth (not toothed) apical margin, striae, including a short scutellary striole, well impressed and finely punctured, interstices convex and with very fine transverse microsculpture, the third with two or three setiferous punctures, epipleura crossed before the apex. Abdominal sternites unpunctured but finely shagreened, especially laterally. Apical abdominal sternite in males smoothly convex; without a median ridge or fovea (cf. P. anthracinus). Tarsi without dorsal furrows, the last segment glabrous ventrally. Front tarsi expanded in males.