Cercyon impressus (Sturm, 1807)

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POLYPHAGA Emery, 1886

HYDROPHILOIDEA Latreille, 1802

HYDROPHILIDAE Latreille, 1802

SPHAERIDIINAE Latreille, 1802

Cercyon Leach, 1817

Cercyon Leach, 1817

This western Palaearctic species occurs across Western, Central and Northern Europe from the Portugal to Italy, Hungary and Ukraine in the south and north to the UK, Denmark, the Baltic countries and Western Russia where it extends to the far north of Norway and Sweden. It is locally common in warmer southern regions but generally common and often abundant in cooler mountain regions, where it occurs up to 2400 m in the Alps and above 1700 m in the Carpathian Mountains, and in the north. It has also become established in parts of Pacific North America following introductions from Europe. In the UK it is generally common throughout England and Wales, including all the islands, and more local further north to Orkney and the Western Isles, it is widespread in Ireland, seemingly common in the north but much more local and scarce in the south. The species is associated with decaying organic matter in almost any situation; it is often common in cattle and sheep dung on pasture or in that of horses, deer and fox etc. in woodland and parkland, it may be common in compost, decaying fungi or among litter in most situations, including wetlands and coastal dunes etc., and it often occurs in disturbed areas such as wasteland and domestic gardens. Adults are present year-round, they may remain active in garden compost or decaying fungi etc. through the winter but they generally overwinter among litter or in moss or tussocks etc and are active over a long season from March until November, peaking in abundance during May or June. Adults are saprophagous while the predatory larvae develop rapidly among host material during spring and summer. Adults may be found by sieving organic matter or in extraction samples at any time but they fly readily on warm days and often occur in flight-interception and dung or fermenting fruit-baited traps in numbers.

Cercyon impressus 1

Cercyon impressus 1

Cercyon impressus 2

Cercyon impressus 2

2.8-3.6 mm. Broadly-oval and continuous in outline, in lateral view the pronotum and elytra smoothly convex (not separately curved), black with elytral apex red or with the forebody black and the elytra brown or darker around the scutellum, antennae brown with darker clubs, palps very dark, legs pale brown. Entire dorsal surface shiny, glabrous and finely and quite densely punctured. Head smoothly convex between small and weakly convex eyes and long converging temples that are usually retracted into the thorax, antennae 9-segmented with a compact and pubescent club, maxillary palps slightly longer than the antennae. Pronotum broadest across rounded posterior angles and strongly narrowed to a curved apical margin, basal margin unbordered and weakly sinuate, surface evenly convex and with a small linear impression in front of the scutellum (may not be obvious). Metasternum with distinct femoral lines which do not reach the anterior margin, anterior margin angled medially; not notched to receive the mesosternal process. Elytra broadest in the basal third and smoothly narrowed to a continuously curved apical margin, each with ten impressed and punctured striae that become weaker towards the apex, interstices flat or weakly convex and finely punctured, about the same as the pronotum. All tibiae with fine spines along the external margin and strong terminal spurs. Tarsi 5-segmnented, the basal metatarsomere longer than the following segments.