Agathidium atrum (Paykull, 1798)
Rather sporadic in occurrence but locally common throughout most of Europe from Spain east to the Balkans and Ukraine and extending north to the Arctic Circle in Norway and Sweden, also widespread across Asia Minor and extending east into Siberia and the far east of Russia (Kunashire Island.) In the UK it is widespread though very local across southern and central England, with the general exception of the West Country, and Wales, including Anglesey, and mush more sporadic and rare further north to the Scottish Highlands. Typical habitats are broadleaf woodland and wooded parkland with plenty of fallen wood and older trees in various stages of decay but individual trees in hedgerows and gardens or on heaths or pasture might also host the species. Adults occur year-round; they overwinter under bark or in decaying wood or leaf-litter and are active from March until September, peaking in abundance during June and July and again, though much less so, in the autumn. They are nocturnally active on dead wood and often occur within or near fungal sporocarps or on wood infested with hyphae, but larvae are thought to develop among slime moulds (Myxomycetes) although no specific associations are known. Adults are easiest sampled at night by searching trunks etc., but they wander on warm evenings and may be found, usually in pairs, on fences or bins etc. in parks and gardens, they may be extracted from samples of decaying wood at any time and they sometimes occur among leaf-litter beneath suitable trees. When disturbed they tend to roll into a ball and drop to the ground.
2.5-4.4 mm. Broadly-oval and strongly discontinuous in outline, body glabrous and shiny black, without microsculpture, underside and appendages reddish brown, usually with the mesosternum and elytral epipleura yellowish. Head broadly transverse, convex and very finely punctured (sometimes the punctures are hardly visible, even at high magnification) between almost flat eyes, temples long and smoothly converging. Antennae inserted anteriorly near the outer margin of the mandibles, 11-segmented with an abrupt 3-segmented club, segment long and slender; about 2.5X longer than segment 2. Pronotum widely transverse, broadest behind the middle and curved laterally to widely-rounded posterior angles and rounded and projecting anterior angles, apical and basal margins curved. Metasternum with distinct femoral lines. Elytra strongly curved from rounded shoulders to a continuous apical margin, surface randomly and very finely punctured (contrasting with the smooth pronotum) throughout and with a sutural stria from the apex which may extend into the basal third, in lateral aspect the humeral angles are very obtuse (about 30 degrees from the basal margin in side view). Legs short and slender, femora not visible in normal setting, tibiae only weakly broadened from the base; with rows of fine spines but without obvious apical spurs. Tarsi 5-5-4 in males, 5-4-4 in females, all segments simple. Claws tiny, smooth and lacking a basal tooth.
Agathidium atrum 1
Agathidium atrum 2