Quedius cruentus (Olivier, 1795)
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POLYPHAGA Emery, 1886
STAPHYLINOIDEA Latreille, 1802
STAPHYLININI Latreille, 1802
Microsaurus Dejean, 1833
This widespread and generally common Western Palaearctic species occurs continuously from Portugal to the Caspian Sea, Asia Minor and North Africa; it extends north into the UK and central provinces of Fennoscandia and has now become established in Eastern Canada and the North Eastern United States, having been first recorded during the early 1980s, presumably from European imports. In the UK it is locally common throughout England and Wales north to the Humber, though it is scarce in the West Country, and very local and scarce further north to the Clyde and across the north of Ireland. Adults may occur among a wide range of decaying organic matter, in the wild among leaf litter, matted grass or decaying wood but they may also be common in artificial habitats such as compost heaps or stored compost/dung mixtures, they also occur under logs and stones etc. in both dry and damp situations but they are probably better known as for their association with trees. In this respect the ideal habitats are open woodland and wooded parkland but they also occur on trees in gardens and on roadsides etc., adults are mostly crepuscular and nocturnal and they may be very active on trunks and fallen timber as they hunt for other insects, they sometimes visit sap and have been found throughout the year in old bird nests and among soft decaying wood in hollows, they spend the day under bark or among crevices in wood but they may also predate larvae of other insects in this situation as they have been found in bark-beetle pheromone traps and under pine bark in company with the scolytid Hylastes opacus Erichson, 1836. We have found the species on a very wide range of broadleaf trees and on ornamental sequoia in our local park, but they are also known to occur on conifers generally and so any species of tree is likely to be worth searching. Little is known of the biology but, typical of the genus, it is likely that both adults and larvae are predatory, adults occur year-round, peaking in abundance from May until July and again in late summer which is usually when they are commonest, they are active through the winter in all but the coldest spells and are among the first beetles to appear on trees early in the year. They have been recorded from many of the common bracket fungi e.g. Laetiporus sulphureus (Bull.) Murrill (1920), Cerioporus squamosus (Huds.) Quélet (1866) and species of Phellinus Quélet (1866), and similarly they may occur in sporocarp samples at any time.
8.0-10.0 mm. Recognized as a member of the subgenus Microsaurus Dejean, 1833 by the moderately large eyes that are about as long as the temples, and the finely and densely punctured elytra, this species is distinctive due to the shiny black body and contrasting red elytra and terminal abdominal segments, there are a few similar species but in the UK this is the commonest of the bicoloured species. Head quadrate or nearly so, with weakly convex eyes and converging, sometimes distinctly-angled, temples before a slightly bulging neck delimited by a transverse impression, surface evenly convex, finely punctured and with strong linear microsculpture. In side view a lateral keel from the neck extends forward under the apical half of the eye. Labrum and maxillary palpi red, antennae red but always darkened apically, sometimes extensively so, antennomeres 5-10 distinctly transverse. Pronotum slightly transverse and more or less continuously rounded from obtuse anterior angles, surface with fine linear microsculpture and a series of three strong punctures either side of the disc in the apical half and others towards the margins. Scutellum large, triangular and shiny black, as the pronotum. Elytra quadrate and weakly dilated from rounded shoulders to separately-rounded apical margins, usually entirely red to reddish-brown but sometimes dark brown with pale sutural and apical margins (specimens with entirely black elytra occur on the continent.) surface with fine overlapping pubescence and long erect setae laterally towards the base. Abdomen finely punctured and shiny, without microsculpture, tergites black with a progressively wider reddish apical border, the fifth usually with the apical third or so rather abruptly red, and the sixth substantially, often completely, pale red. Legs entirely red. Males may be recognized by the more dilated front tarsi and the excised apical margin of the sixth abdominal sternite. Among our UK fauna most likely to be confused with Q. aetolicus Kraatz, 1858, this also has contrasting pale elytra and apical abdominal tergites but the pale apical margin to the fifth (visible) tergite is narrower, about a quarter of the length of the tergite. Doubtful males may be dissected as the paramere of cruentus is less dilated towards the apex.