Pterostichus diligens (Sturm, 1824)
This species is generally common from lowland to alpine elevations throughout Europe with the exception of some areas of the Balkan Peninsula, it extends from northern Spain to Greece and further east through Asia Minor and Russia to eastern Siberia, to the north it reaches the UK and the northernmost parts of Fennoscandia and is present on Faroe and Iceland where it occurs among moss and peat beside geysers. In the UK it is common throughout the mainland and occurs on all the islands, it is generally common across Northern Ireland but more local and scattered in the south. Typical habitats are wetland margins, permanently damp woodland and grassland, peat bogs and upland moors, usually on humus-rich soils in shaded situations, they are common in coastal areas but they seem to avoid unvegetated areas on sand and heavy clay soils. Adults are present year-round, peaking in abundance during June and July and again in September and October, they overwinter among litter, moss and tussocks away from marginal areas prone to flooding but also in reed and rush stems but are often active during mild spells, they are otherwise primarily nocturnal and terrestrial although they are often active during the day in damp and shaded situations, they are good colonisers and while the majority of UK specimens are brachypterous the proportion of fully-winged specimens varies on the continent where they have been observed in flight. Breeding occurs from late March until June or early July and larvae develop through the summer to produce new-generation adults from July until October; the latest eggs may produce larvae that overwinter and pupate in the spring but this probably applies to only a very small number. Both adults and larvae are predatory but also consume a small proportion of plant debris, the main prey are small springtails and mites but they have also been recorded feeding on aphids, spiders, various plant bugs and early stages of small insects. Adults are easily sampled by searching among litter etc in damp habitats; they sometimes occur in numbers, especially in spring and autumn, and usually among other wetland carabids, including the closely-similar P. strenuus (Panzer, 1796), and so specimens will usually need to be taken for careful examination.
Pterostichus diligens 1
Pterostichus diligens 2
Pterostichus diligens 3
5.3-7.0 mm. Body shiny black, legs black or dark brown, antennae black or dark brown with at least the basal segment lighter. Head with large and moderately convex eyes and short converging temples, surface smoothly convex and very finely punctured, with two setiferous punctures beside each eye, antennae densely pubescent from the fourth segment. Pronotum slightly transverse, broadest about the middle and evenly curved to a sinuate margin before perpendicular posterior angles, basal fovea single, linear and without an external ridge, basal punctation fine and sparse, prosternum dull and unpunctured above the coxae. Elytra with sloping shoulders and almost parallel-sided to a continuously-curved apical margin, each with eight impressed and finely punctured striae and a short scutellary striole, interstices flat or weakly convex; the third with three setiferous punctures, epipleura crossed before the apex. Apex of front tibiae broadened beyond the antennal-cleaning notch. Tarsi without dorsal furrows, the basal segments of the front tarsi dilated in the male.