Proteinus brachypterus (Fabricius, 1792)
This species is locally abundant throughout the western Palaearctic region, including north west Africa, and is generally the most common and frequently recorded member of the genus in central and northern Europe, it extends north to the UK and beyond the Arctic Circle in Fennoscandia and occurs on Faroe, to the east it is widespread in western Russia and the Near East and it has been widely recorded in The United States and Canada since the late nineteenth century. Here it is very common throughout England and Wales and rather local and sporadic further north to Orkney, it occurs on Anglesey and Man and is very local in the north of Ireland. Adults are active year-round; they occur from lowlands to the subalpine zone and have been recorded in Norway through the winter from pitfall traps under placed under snow in northern forest regions. The species occurs among all kinds of decaying organic matter in almost any not too dry habitat; it has been recorded from dung, carrion, compost, tussocks, detritus under bark and at sap but large numbers commonly occur among decaying bracket fungi; brackets on trunks and branches may host them but terrestrial fungi seem to be a favoured host, especially in the autumn and through the winter among large decaying brackets that have wilted and formed wet layered structures in contact with the ground, they remain common through the winter and large numbers may be found in the spring by sieving or breaking such material onto a tray. In general adults will only be found by sieving or taking samples for extraction but working any damp compost or leaf-litter is likely to prove productive, especially in the spring and autumn. Adults are thought to be saprophagous, feeding on decaying material of both plant and animal origin, but details of the larval development are not well understood.
Adults are small, 1.5-1.9mm, broadly-oval in form, very finely pubescent and dark brown with the legs and the basal antennomere contrasting pale brown, the body is clearly and usually strongly microsculptured and so appears rather dull. P. brachypterus may be distinguished among our UK species by the very fine raised border along the basal pronotal margin, the strong microsculpture and the form of the antennae; dark with a pale basal segment and the eighth segment distinctly transverse. Head with large convex eyes and short, strongly converging cheeks and temples, vertex with two wide longitudinal depressions so appearing widely ridged medially. Two basal antennomeres long and broad, 3-7 quadrate or nearly so and 8-11 forming a gradual but narrow club. Pronotum widely transverse, rounded and finely margined laterally and evenly convex. Elytra quadrate or slightly elongate, curved laterally and broadest about the middle, the surface lacking striae and rather densely punctured throughout. Abdomen usually shorter than the elytra, with three or four tergites visible, the basal tergites with strongly raised lateral margins, very finely and evenly punctured throughout. Males may be distinguished by the presence of dense and very fine tubercles along the inner margin towards the apex of the middle tibiae.