Quedius plagiatus Mannerheim, 1843
This Holarctic species occurs throughout Europe although it is sporadic and generally rare, occurring mostly in upland and mountain conifer forests where its typical habitat is beneath the bark of a range of coniferous trees e.g. spruce, fir, cedar and, especially, pine but it has also been recorded from beech and maple; in North America and Canada, where it is locally common, it is more or less confined to northern conifer forests. Adults and larvae occur year-round under moist bark on decaying and dead standing trees, fallen timber and logs; adults are active from spring to autumn, peaking during June and July; they remain concealed during the day and hunt on the surface and disperse by flight nocturnally. Both adults and larvae are predatory and both are generally associated with the galleries of scolytids and other insects; in a recent Swedish study they were found to be a significant predator of Ips typographus (Linnaeus, 1758) in conifer plantations and they have been shown to be attracted to Ips semiochemicals. In the UK it is locally common in 3 general areas; Northern England, Southern Scotland and the north west Highlands, it also occurs sporadically south to East Anglia and it is widespread in Ireland but it is otherwise absent from England and there are only old records from Wales. Here the adults have been recorded from March to November, usually beneath conifer bark but also from moss and fungi on fallen timber and logs.
This fairly large staph is easily recognised by the colour, the relatively small eyes and the glabrous and shiny elytra. 7-9mm. Head and pronotum black, elytra entirely red or obscurely darker on the disc. Head transverse with weakly convex eyes that occupy about half the lateral margin, vertex with linear microsculpture and scattered tiny punctures, antennae dark with various basal segments red and segments 5-10 transverse. Pronotum transverse, with a series of 3 setiferous punctures either side of the middle in the anterior half, the surface microsculptured or punctured as the head, when illuminated from certain angles strongly iridescent greenish bronze. Elytra elongate, the surface glabrous and shiny although overall rather roughened in appearance, with very fine punctures set in a field of weakly transverse microsculpture, and two series of larger setiferous punctures; one near the suture and one on the disc. Scutellum large, triangular and coloured and microsculptured as the pronotum. Elytra parallel-sided or widened around the middle, tapering towards the apex after fourth segment and dark brown with the apex of the segments variously paler. Legs mostly red or variously darker towards the base.