Sunius melanocephalus (Fabricius, 1793)
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POLYPHAGA Emery, 1886
STAPHYLINOIDEA Latreille, 1802
PAEDERINI Fleming, 1821
Sunius Stephens, 1829
Native to the Palaearctic region and known from Europe to Eastern Russia and China, this species was recognised in North America in 1991 from specimens collected in 1924 and it has now been found to be established at several sites in the northern United States and Eastern Canada. The species is locally common across Southern and Central Europe from Northern Spain to Greece but much less so further north where it reaches the UK, Denmark and into the southernmost provinces of Sweden. In the UK it is widespread across Southern and Central England and South Wales although with the exception of the midlands, where it is frequently recorded, it tends to be very local and generally scarce. Here it usually occurs in open grassland and among vegetation on permanently damp soils, but on the continent and in North America it is more widely eurytopic, occurring in damp woodland, marshland, wetland margins, arable land, as well as disturbed sites such as parkland and gardens, and adults have been recorded from ant-nests and terrestrial mammal burrows. The species is wing dimorphic throughout the range and adults occasionally occur in flight-interception traps but, with the exception of southern Turkey where the macropterous form is more common, larger winged forms are generally rare. Adults are present throughout the year; they overwinter in tussocks or among litter etc and are active from late winter until the autumn, with peaks of abundance in May and June and in August and September. Specimens sometimes occur when sweeping grassland etc, and pitfall traps may produce them in numbers (although adults are mainly nocturnal), they may occur in flood-refuse at any time, and taking samples of moss and litter etc may produce them in small numbers.
3.2-3.8 mm. A rather flat and parallel-sides species, head dark brownish, pronotum pale brown, elytra dark brown with paler margins, abdomen dark with the apical margins of the tergites narrowly pale, antennae pale or with some segments darker, penultimate maxillary palpomere dark, legs pale. Head slightly elongate with temples at least 1.5X longer than the eyes and rounded at the base, surface smooth between scattered strong punctures, labrum convex with two median tubercles. Antennae filiform with all segments elongate, the basal segment about as long as the next two combined. Penultimate maxillary palpomere broadly oval, terminal segment diminutive. Gular sutures broadly separated and converging anteriorly, the cuticle between smooth and glabrous. Neck narrow, much less than half the head width. Pronotum quadrate, parallel-sided or slightly narrowing to the base, angles smoothly rounded, basal and apical margins straight, surface smooth and punctured as the head except for a narrow unpunctured median strip, lateral margins with several large dark setae. Elytra variable; in short-winged forms slightly shorter than the pronotum, otherwise slightly longer, a little broader than the pronotum and slightly dilated from rounded shoulders to recurved apical margins, surface without microsculpture, punctured throughout and with the sutural margin raised towards the base. Abdomen finely punctured throughout, the tergites evenly convex and not depressed across the base, the seventh much longer than the others. Femora long and broad, tibiae long and only slightly widened from the base. Tarsi 5-segmented with the fourth segment narrowly lobed; front tarsi only slightly wider than the others in both sexes, and the basal segment of the hind tarsi slightly longer than the second segment. In males the eighth sternite has a small apical incision.