Agathidium varians Beck, 1817
This Western Palaearctic species is locally common throughout Europe from Spain to Greece in the south and north to the UK, Denmark and the Baltic countries, reaching north to the Arctic Circle in Fennoscandia, also known from Algeria and parts of European Russia. In the UK it is generally common in Southern and Central England and across the northern half of Wales, but much more local and rare further north to the Scottish Highlands and in Northern Ireland. The typical habitat is old deciduous or mixed woodland and wooded parkland with plenty of mature trees in various stages of decay, but adults sometimes occur on individual trees in gardens or hedgerows etc. and we have found them repeatedly on willow trunks and fallen timber in local Carr and other wetland situations. Adults are present year-round, they overwinter under bark or among decaying wood or old leaf-litter and are active from March until November, peaking in abundance during April and May. The species is crepuscular and nocturnal; adults sometimes disperse over short distances by flight on warm spring and early-summer evenings but they are otherwise active on trunks and branches, especially low down on trees or in the vicinity of fungal sporocarps or slime moulds, they sometimes occur under or even within fungi but the larvae are thought to be associated exclusively with slime moulds. Adults usually occur as single specimens or, especially in the spring, as pairs which usually consist of a male and a female, although numbers may occur in flight-interception traps placed in suitable trees. Little is known of the biology and specific host associations have not been established, adults are known to spread spores of Ganoderma applanatum (Pers.) Pat but are otherwise known from a range of fungi on a wide range of deciduous trees and it seems likely that dense and shaded woodland is the preferred habitat, it is likely that breeding and larval development occurs in spring and summer as teneral adults have been recorded in late summer and autumn. During the winter they sometimes occur in samples of decaying wood or well-decayed leaf-litter and specimens have been found in old bird nests.
2.5-3.2mm. Elongate and strongly discontinuous in outline although adults are able to curl-up into an almost spherical ball with the head and appendages retracted, dorsal surface very shiny and with weak reticulate microsculpture; head and pronotal margins usually pale to dark brown, pronotal disc and elytra dark brown to black, antennae pale brown with segments 9 & 10 darker, legs pale brown. Head broadest across weakly convex eyes, temples long and converging with a short (less than one-third the eye length) and rather strongly angled ridge immediately behind the eye, surface finely and sparsely punctured, clypeus with two depressions and sometimes small transverse ridges between the eyes, anterior clypeal margin weakly incised. Antennae inserted anteriorly in front of the eyes, 11-segmented with a loose 3-segmented club; segments 2 & 3 subequal, 4 elongate, 5 & 6 quadrate and 7 & 8 transverse. Pronotum strongly transverse and very convex, broadest about the middle and narrowed to rounded posterior angles and projecting anterior angles, basal and apical margins curved, lateral and basal margins finely bordered, surface sparsely and very finely punctured. Metasternum without femoral lines. Elytra slightly broader than the pronotum and appearing almost circular from above, smooth and shiny with punctures sparser and finer than those on the head and pronotum, finely bordered laterally, without striae but with a sutural stria from the apex to about the middle, humeral angle obtuse, about 50 degrees with respect to the lateral margin. Legs short and slender with femora not visible in normal setting. Tibiae narrow throughout; gradually widened from the base to truncate apices and all with obvious, if tiny, apical spurs. Tarsi 5-5-4 in males, 4-segmented in females, all segments simple but basal protarsomeres slightly dilated in males.