Philonthus decorus (Gravenhorst, 1802)
This is a widespread and generally common species throughout England and Wales, with the probable exception of the West Country but including Anglesey and Man, and though more local and scarce further north extending to the far north of Scotland and Orkney. It is widespread across central Europe though sporadic; generally more common in northern and mountainous areas though rare in e.g. Poland, extending north into Fennoscandia, south to the Pyrenees, Italy and the Balkans and east to (at least) western parts of Siberia. Typical habitats are damp woodland and densely vegetated marginal areas, in upland situations often under rocks or among stones beside streams and bogs and on the continent among sphagnum bogs etc. in mountain areas. Adults occur year-round and are generally active from March to October with peaks in May and September, they overwinter under logs or among moss or leaf-litter and may become active during mild spells; they are nocturnally active on the ground and may be seen by torchlight as they move rapidly hunting for snails, slugs and small insects. During the summer they may occur in numbers under large logs and where several of these lie close together each may all harbour a small group of specimens, adults will almost always be found in damp and shaded habitats throughout the year and only rarely venture out onto pathways or open ground during the warmer months. Mating occurs mostly during the spring population peak around May and oviposition begins soon afterwards; eggs are laid singly in the soil and each female will lay around 20, this may continue into July although by this time very few are still laying, and at least some of this population will go on to overwinter and oviposit for a second time. Larvae develop through the summer and pass through 3 instars before pupating during September; they are generally predaceous and at this time have been recorded consuming eggs and larvae of winter moths, along with various other staphs and carabids, and may become a controlling factor when moth populations are large. New generation adults appear from September, producing a second population peak, and will feed until the winter when they become inactive. Adults will soon be recognized in the field; the large size, metallic colouration and contrasting shiny forebody and matt elytra are distinctive.
10-14mm. Head and pronotum black with a green or sometimes coppery-green metallic reflection, elytra dull metallic green, scutellum and abdomen black. Head variable but usually quadrate, or nearly so, with relatively long and curved or obscurely angled temples and large, weakly-convex eyes. Vertex smooth, with quite strong cellular microsculpture and a few scattered larger punctures, clypeus deeply notched medially and with a series of long and stout setae anteriorly, mandibles large, robust and produced forward when at rest, palps dark or lighter towards the apex, with all segments long and slender. Antennae inserted within the outer margin of the mandibles; with all segments elongate, becoming less so towards the apex; the penultimate segment near-quadrate. Pronotum quadrate, rounded laterally and across the base, the posterior angles rounded, the surface with strong cellular microsculpture and a series of 4 large setiferous punctures either side of the middle; the first near to the anterior margin and not in line with the others, and occasionally one may be missing. Scutellum large, triangular and punctured and pubescent as the elytra. Elytra transverse with sloping shoulders and an angled basal margin, the surface dull from rather dense punctation and strong granular microsculpture, pubescence overlapping and quite dense, directed parallel to the suture. Abdominal segments finely and densely punctured and pubescent but for a narrow, smooth and shiny basal strip, microsculpture dense and fine but obvious below the pubescence, a fine raised line across the base of the basal segments straight. Legs long and slender, especially the middle and hind tibiae, usually extensively dark with lighter tarsi.