Hister unicolor Linnaeus, 1758
This is the largest common histerid in the U.K. and despite its generally concealed lifestyle should quickly be found by the beginner. The species is widespread and usually common throughout Europe from the Mediterranean to Scandinavia and east through Asia. In the U.K. it is locally common throughout England and Wales north to the Scottish border although records are more scattered in the north. It occurs in a range of habitats including parkland and coastal dunes but shows a preference for woodland and dung pasture. Both Adults and larvae feed on soft-bodies insects, especially diptera larvae, among decaying organic matter; fungi, compost and carrion but especially horse and cattle dung where they are usually among the first insects to colonize fresh material. Adults have been observed in mammal and bird nest detritus, and feeding at sap, they are nocturnal and occasionally come to light. They detect new material by smell and accordingly may be found among large decomposing fungi and carrion in large numbers and may readily be surveyed using baited traps. Adults are active from April or May and breed in late spring. Eggs are deposited into the medium and hatch within 4 or 5 days, larval development is rapid with each instar taking 3-7 days to develop and the pupal stage takes a week or so. New generation adults arrive in mid or late summer but activity is low during hot weather and so they may not be obvious until the autumn, at this time they may briefly be abundant as the generations overlap. When disturbed they withdraw the appendages into the body and remain still for some time and so may be overlooked, they are often infested with phoretic mites (Uropoda spp.)
A large and broadly oval histerid; smoothly rounded in outline. 7-10mm and entirely dark but for the red palps and antennal funiculus, and the brown pro-tarsi. Upper surface smooth and glabrous, generally shiny but this fades on older specimens. Head transverse with the eyes partially hidden under the pronotum. Clypeal border with a well-impressed line which may be eroded anteriorly. Antennae with scape long and curved, the funiculus 7-segmented and a 3-segmented club. Pronotum transverse with prominent front angles and an impressed line inside the anterior and lateral margins, between this and the margin there is a smaller line from the front angles to about the middle. Scutellum small and triangular. Elytra transverse, impunctate and with well impressed striae; 1-3 complete but stopping short of the base and apex, 4,5 and the Sutural striae present apically, 5 shorter and often interrupted. Humeral stria more finely impressed. Two sub-humeral striae present; a short outer one near the middle and a longer one inside this from the basal third to the apex. Apices truncate. Meso- and metatibiae dilated and each with 4 rows of spines and strong apical spurs. Protibiae with 3 large teeth along the external margin, the apical being bifid, although these quickly become worn in life. The external face has a longitudinal groove to receive the tarsi when the beetle ‘rolls up.’ Meso- and metatarsal segments have strong spines at apex. All claws smooth.