Cercyon melanocephalus (Linnaeus, 1758)

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POLYPHAGA Emery, 1886

HYDROPHILOIDEA Latreille, 1802

HYDROPHILIDAE Latreille, 1802

SPHAERIDIINAE Latreille, 1802

Cercyon Leach, 1817

Cercyon Leach, 1817

Widespread and generally common throughout central and northern Palaearctic regions, this species occurs throughout Europe to the UK and the far north of Fennoscandia, it is present in Iceland and the Channel Islands but absent from North Africa and the Middle East. It is among the most common dung beetles in the UK, occurring in a wide variety of habitats north to the Western Islands and Shetland and throughout Ireland although only sporadically in the south. Adults occur in herbivore dung generally and may be abundant in sheep and cattle dung, they also occur more generally among decaying organic matter although less frequently so, they have been recorded from old bird nests and we have found them in composted grass cuttings and pond clearance and, in large numbers, among decaying terrestrial bracket fungi in the autumn and early winter. They are present year-round and may be found over a long season from early March although they are often active during mild winter spells; they fly well and rapidly occupy new host material in the summer, often along with other members of the genus, and frequently occur at light and flight-interception traps. The species breeds in the spring and summer and adults peak in abundance during May and June, it is thought to be univoltine in northern parts of its range although there is often a second peak in adult abundance later in the summer (which might suggest a second generation); eggs are laid in a silken cocoon among the host material and larvae develop rapidly, producing new-generation adults through the summer. Adults are easily sampled by searching through dung and they may be abundant in very wet samples which they virtually swim among, they will soon arrive at dung-baited traps and may be netted in flight above dung pasture in warm weather, they are frequent among flood-refuse and may occur in extraction samples through the winter.

This relatively large species (at least among the genus) can usually be recognised in the field by its very distinctive bicoloured elytral pattern; substantially pale to dark red with a variable but well-defined triangular black mark around the scutellum and dark epipleura, it may casually be mistaken for C. haemorrhoidalis, another common species with which it often occurs, but here the dark elytral pattern forms a T-shape from the base. 2.2-3.0mm. Head shiny black, finely punctured but lacking microsculpture, anterior clypeal margin gently sinuate, antennae pale to dark brown with a black club, palps black or very dark brown and as long as the antennae. Pronotum entirely black, broadest between obtuse posterior angles and narrowed to rounded (from above) anterior angles, lateral margins finely bordered, surface finely punctured and sometimes weakly impressed before the scutellum. Metasternum with distinct femoral lines which do not reach the anterior margin and a long and narrow median process. Scutellum slightly elongate and more finely punctured than the adjacent elytra. Elytra broadest before the middle and smoothly narrowed to a continuous and rounded apical margin, each with 10 impressed and punctured striae which tend to fade towards the base, the tenth often present in the basal half, interstices flat and randomly punctured. The triangular black mark around the scutellum varies in size; it usually extends to the basal third but may be longer, the brown ground colour varies in depth and may be lighter towards the apex, in which case the sutural interstice is often darker, and the epipleurs are always dark. Legs pale to dark brown, usually with paler tarsi, all tibiae with strong external spines, middle and hind tibiae with two long and unequal spurs at the inner apical angle and the front tibiae rounded apically. Tarsi 5-segmented; the basal segment longer than the second and the claws smooth and curved.

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