Quedius mesomelinus (Marsham, 1802)
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POLYPHAGA Emery, 1886
STAPHYLINOIDEA Latreille, 1802
STAPHYLININI Latreille, 1802
Microsaurus Dejean, 1833
Native to the Palaearctic region and probably Holarctic, having been proven to occur in North America since the early 17th century, this species is now almost cosmopolitan following introductions to Australia, New Zealand and South America and many other areas including Greenland, it is generally common throughout Europe north to the UK and far above the Arctic Circle in Fennoscandia, Faroe and Iceland, it is known from North Africa and extends east through Asia Minor and Siberia to the far east of Russia. In Europe it occurs from lowlands to the Alpine regions while across Asia it is more or less boreo-montane, being restricted to mountain areas in the south while occurring more generally further north. Here it is generally common across Southern and Central England and Wales and more local and scarce in the West Country, further north to the Scottish Highlands and in Northern Ireland. The species occurs in a wide range of habitats; it is mostly subterranean and often associated with mammal nests but also occurs among decaying wood in tree hollows and under bark, it often occurs in sheds, barns and cellars, across Europe is among the most common rove beetles in caves and disused mines and may be common on disturbed land including domestic gardens. Adults occur year-round; they overwinter in a variety of habitats although are seldom recorded at this time, they are active over a long season from March until November and peak in abundance from May until July and again in the autumn. Both adults and larvae are predacious and might be expected in any habitat with a good supply of fly larvae etc., e.g. decaying fungi and compost. Breeding is thought to occur in spring and early summer as a pupa has been found in a Badger set in August (Lott, 2011). Adults are mostly nocturnal, they may be found by searching under logs and debris on damp grassland and woodland by day or by sieving compost etc. at any time, on warm nights they often run in the open on pathways and logs and frequently climb trunks in open woodland and parkland. So far as is known all specimens are fully-winged, they fly well and occasionally come to light.
7-11 mm. Elongate with a small head and almost parallel-sided abdomen, head black with the labrum and mandibles paler, pronotum and scutellum black or dark brown, elytra dark brown, usually paler along the suture and apical margins and often with a faint metallic reflection, abdomen dark brown, often paler towards the apical margin of the tergites, legs reddish with the femora and tibiae to some extent darker. Maxillary palps dark brown or with the terminal segment darker, antennae reddish-brown with three basal segments darker. Head quadrate with large protruding mandibles, lateral margin evenly curved to a short neck, the eyes following the contour and more-or-less as long as the temples, surface smoothly convex, with two large setiferous punctures near each eye and several towards the base, otherwise with micropunctures scattered among fine linear microsculpture. Antennae with three basal segments elongate, 4 and 5 quadrate or slightly elongate and 6 to 10 slightly transverse. Pronotum transverse, broadest near rounded posterior angles and narrowed to a rounded anterior margin, surface with fine linear microsculpture, a series of three setiferous punctures either side in the anterior half and several others near the basal and lateral margins. Scutellum large, triangular and with scattered fine punctures, usually entirely black but often paler along the lateral margins. Elytra quadrate, slightly dilated from sloping shoulders to separately rounded apical margins and randomly punctured throughout and with fine overlapping pubescence. Abdomen strongly bordered laterally, tergites not or only vaguely impressed across the base, finely punctured and pubescent throughout and without microsculpture, apical tergites sometimes finely wrinkled or slightly iridescent. All tibiae with two large spurs, front tarsi more strongly dilated in males. Median lobe of aedeagus dilated from the middle and evenly rounded to a widely obtuse apex (in ventral aspect), in lateral aspect almost straight to a distinct angle about 2/3 from the base, then very uneven to the apex.
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Very similar to Q. maurus (Sahlberg, 1830), but here the median lobe is obtusely angled towards the apex (in ventral aspect) and in lateral aspect externally more-or-less evenly curved from base to apex and almost straight internally.