Cercyon haemorrhoidalis (Fabricius, 1775)
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POLYPHAGA Emery, 1886
HYDROPHILOIDEA Latreille, 1802
SPHAERIDIINAE Latreille, 1802
Cercyon Leach, 1817
Cercyon Leach, 1817
Originally widespread through the western Palaearctic this species is now Holarctic; it has spread widely in Asia and become established and widespread in North America and Canada, it has also become established in New Zealand and temperate areas of south-eastern Australia and has been recorded from the Philippines and Argentina. In Europe it occurs from the Mediterranean to the far north of Fennoscandia although it is absent from some of the islands and from North Africa, and it occurs from lowlands to above the tree-line in mountain areas, its occurrence is sporadic but for the most part it is common and often abundant. In the UK it is abundant across Wales and the south of England but more local in the West Country and further north to Orkney and Shetland, it is generally common in the north of Ireland but local and generally coastal in the south. Adults are present year-round and active over a long season from early spring, they are terrestrial and often abundant in herbivore dung in almost any situation, especially in horse and cattle droppings, but also occur in all kinds of decaying organic matter including compost, fungi, carrion and accumulated leaf-litter, and have been recorded from various mammal and bird nests and at sap. Numbers peak in late spring and late summer but adults may be variably abundant through the spring and summer, they seem to avoid very wet dung but will otherwise rapidly colonize most freshly deposited samples, they may often be seen flying over dung pasture in the evening or during the warmest days and they may come to light traps in numbers. Little is known of the biology but members of the genus display wide variation in the number of generations per year, larval development in the present species takes about three weeks and maturation feeding and dispersal of the adults may be prolonged but it seems likely that in the UK they may be multivoltine or there may be overlapping generations depending on local conditions. Both adults and larvae are thought to be saprobic.
2.5-3.2mm. Elongate and broadly-oval, this species may be recognized by the dark body and elytral colouration; dorsal surface shiny and lacking microsculpture, forebody entirely black, elytra very variable from extensively pale to extensively dark but usually with at least interstices 2-4 towards the base and the apex pale, characterized by the narrowly dark basal margin and suture producing a T-shaped mark which is visible even in extensively dark specimens by lifting or wetting the elytra, and the epipleurs are always mid to pale brown, never black. Legs variably brown, usually with paler tarsi, and palps and antennae black or very dark brown. Head and pronotum finely and quite densely punctured, pronotum evenly convex and not impressed in front of the scutellum, metasternum with distinct femoral lines extending obliquely from the coxae towards the anterior margin. Each elytron with ten well-impressed and finely punctured striae extending from near the basal margin to the apex, all interstices finely and randomly punctured throughout. All tibiae with a row of fine spines along the external margin and strong terminal spurs. Tarsi 5-segmented, the basal metatarsomere longer than those following.