Pterostichus strenuus (Panzer, 1796)
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ADEPHAGA Clairville, 1806
PTEROSTICHINI Bonelli, 1810
Steropus Stephens, 1828
A common and often abundant species throughout Europe except for a few areas bordering the Mediterranean, it extends north to the UK and the far north of Fennoscandia and east through Asia Minor and Mongolia to the Amur region of Russia, it is absent from North Africa and the Atlantic islands but following introductions from Europe has become established in the United states and Canada. Here it occurs throughout the UK, including all the islands, and is among the most common members of the genus. Adults live for more than a year and so occur year-round, they are active over a long season from early spring and peak in abundance during late summer and autumn, they are sometimes quoted as being wetland beetles but are actually eurytopic and occur in a wide range of both wet and dry habitats. Adults overwinter among litter and tussocks or under logs etc and may migrate from their summer quarters to do so, they become active during February or March and are generally nocturnal but may also be found active during the day. Typical habitats are among litter and moss in woodland and parkland or on wetland margins but they may be common on damp grassland, arable land and heaths and they often occur on disturbed sites such as wasteland and domestic gardens, they are wing dimorphic and most specimens show some reduction in wing development, flight has been observed but only infrequently and may only be used for dispersal as some females have displayed flight muscle autolysis after egg maturation. Mating occurs from late March until July and larvae develop between June and August, pupation occurs in the soil and new-generation adults emerge from early September. Both adults and larvae are terrestrial predators and both are known to take at least some plant food as well, they hunt among litter etc but adults also hunt on the surface and so may be found by searching pathways and grass at night. Pitfall trapping often produces adults in numbers but they will soon appear when searching litter or under debris in all but higher mountain habitats, they generally occur among populations of other carabids and as there are several superficially similar species they will need to be examined carefully.
5.0-7.0 mm. Body shiny black, legs variable but usually substantially pale brown, palps pale but variably darkened towards the apex, antennae dark with at least three basal segments mostly pale. Head with two setiferous punctures beside each eye, terminal segment of maxillary palpi at least as long as the penultimate. Pronotum broadest in front of the middle and sinuate before sharp posterior angles, the margin just in front of the angles more-or-less straight, disc evenly convex and unpunctured, basal third variably punctured and with a single long fovea each side, these without an external keel. Prosternum shiny and punctured above the coxae (visible from side view). Elytra with a scutellary striole, three setiferous punctures joining the third atria and the epipleura crossed before the apex.