Deleaster dichrous (Gravenhorst, 1802)

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POLYPHAGA Emery, 1886

STAPHYLINOIDEA Latreille, 1802

STAPHYLINIDAE Latreille, 1802

OXYTELINAE Fleming, 1821

DELEASTERINI Reitter, 1909

Deleaster Erichson, 1839

This native western Palaearctic species occurs sporadically from lowlands to low mountain altitudes throughout Europe from the Mediterranean north to the UK and southern provinces of Fennoscandia, it is also present in North Africa and extends east into Turkey, Iran, Russia and the Caucasus, and has become established from introductions in the United States since the 1930s, and Canada since the 1960s. In the UK it is locally common in Wales and western and northern England, and more sporadic and rare further north to the Scottish Highlands and through Ireland. Here it is mainly associated with exposed riparian substrates, often where they are partly shaded and with patchy vegetation, but it has also been recorded from silage stores. On the continent they are more eurytopic, occurring in open damp grassland, damp woodland, seashores and dunes and in disturbed situations such as landscaped woodland, waste ground and urban parks, they are also at least partly synanthropic as they occur in domestic gardens and, in the United States, in damp basements as well as in wetland marginal situations. Adults occur mostly between May and August, they predate other insects etc. and live among gravel and stone debris, under logs and rocks or among moss, they may be active during the day but are probably mostly nocturnal as they regularly arrive at MV light traps. They run quickly and can be very difficult to capture, and when alarmed they raise the abdomen and produce a defensive fluid from paired apical glands, this seems to be harmless to humans and acts like an adhesive to deter other foraging insects.

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6.5-7.0mm. Very distinctive among our fauna due to the large size and colour; head black, pronotum, elytra and appendages pale brown, and abdomen dark brown to black, head and pronotum with sparse semi-erect pale pubescence, elytra with dense recumbent pale pubescence. Head with large convex eyes and long, curved temples that converge to a short neck, vertex with a transverse angled impression from behind the eyes, labrum and palps contrasting pale brown, terminal maxillary palpomere not expanded. Antennae 11-segmented and filiform, all segments elongate; the second much shorter than the first and third. Pronotum widest in front of the middle and narrowed to rounded anterior and posterior angles, surface evenly and weakly convex, and without well-defined depressions. Elytra much wider than the pronotum, with broadly rounded shoulders and only weakly dilated towards rounded posterior angles, apical margins separately rounded, and surface without striae but variably depressed behind the scutellum, pubescence oblique around the scutellum but otherwise mostly directed apically. Abdomen with wide and strongly-raised lateral margins, the tergite finely punctured and pubescent and with very fine transverse cellular microsculpture. Legs long and slender, femora and tibia smooth and unarmed, tarsi 5-segmented.

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