Nossidium pilosellum (Marsham, 1802)
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POLYPHAGA Emery, 1886
STAPHYLINOIDEA Latreille, 1802
PTILIINAE Erichson, 1845
Nossidium Erichson, 1845
A widespread though very local and sporadic species; it is locally common across Southern and Central Europe from Spain to the Black Sea though absent from most of the Balkan Peninsula and Greece, it extends north into the Netherlands, Denmark, Germany and Poland but is otherwise absent from the Baltic region, the eastern extent of the range seems to be central parts of European Russia, and so far as is known it is absent from the Mediterranean islands and North Africa. In the UK it is widespread though local across Southern England and Wales and there are a few records further north to the Tyne and in Ireland. Adults are most frequently recorded from decaying wood of a range of broadleaf trees and shrubs, often where they are infested with fungus and sometimes in the vicinity of nests of the arboreal ant Lasius brunneus (Latreille, 1798); beyond this they sometimes occur among moss and terrestrial fungi in wooded situations. The biology is only poorly understood but adults have been collected from the fungus Russula integra (L.) Fr. on conifers in Europe and there seems to be a general association with Cerioporus squamosus (Huds.) Quélet (1866) as numerous adults have been found among decaying wood where these fruit in hollows on a range of broadleaf trees, but it is likely to be a more generally mycophagous as large populations are occasionally associated with other species of Polyporaceae. Adults occur year-round, they overwinter among decaying wood or in moss or litter close to such material and are often active at this time, they are otherwise active over a long season from early spring and are generally most common from May until July. The larva has been described in some detail by Kilian and Burakowski who note also that the species has been reared from egg to adult in 24 days and that both larvae and pupae were observed during July and fresh adults were recorded into September. Adults may occur in samples of decaying wood at any time of year but during the winter are equally likely to be found among moss and litter, they generally occur in numbers and, despite their very local occurrence, sometimes in very large numbers.
1.1-1.3 mm. Elongate-oval, continuous in outline and rather strongly convex, entirely dark to pale brown, sometimes with paler pronotal angles, and with very fine overlapping pale pubescence, dorsal surface smooth but underside with distinct reticulate microsculpture. Head only narrowly visible from above, convex and finely punctured between relatively large and convex eyes, labrum trapezoidal, antennae 10-segmented, the basal segment much broader than those following and 8-10 forming an elongate and loose club. Pronotum broadest across acute and produced posterior angles and smoothly rounded anteriorly, lateral margins strongly bordered, basal margin much more finely so, and surface finely but not densely punctured, evenly convex and without structure but for a weak but usually well-defined median line before the base. Scutellum small but obvious, straight-sided and triangular. Elytra broadest behind rounded shoulders and smoothly narrowed and curved to the apex, which completely covers the abdomen, without striae although the sutural margin tends to be slightly raised, and finely but not densely punctured throughout. Elytral epipleura separated from the lateral surface by a moderately strong keel. Metasternum and abdominal ventrites with rather long golden or yellowish pubescence, front coxae narrowly divided by a small and parallel-sided process, middle coxae more widely separated, hind coxae divided by a very narrow and forked metasternal process. Males may be distinguished by the smoothly rounded pygidium, in females this is produced medially into five or six teeth.
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​Distinguished among our UK species by the small size, rounded elytral apices which cover the abdomen, bordered elytral epipleura, and divided front coxae and small scutellum.