Anisotoma orbicularis (Herbst, 1792)
A widespread and locally common species throughout Europe from Portugal to Italy and the Balkan Peninsula in the south, although apparently absent from Greece and the Mediterranean islands, and extending north to the UK, Denmark and into Northern provinces of Fennoscandia. Further east it has been recorded from Asia Minor and Central and Eastern Russia. Most records are from lowland sites although it has been recorded up to 2200m in Austria and, along with A. humeralis (Fabricius, 1792); it is generally the most common European member of the genus. In the UK it occurs locally across England and Wales north to the Humber although it is generally absent from the West Country, there are scattered records further north to the Scottish border and an a very few modern records from Ireland (Fermanagh). Typical habitats are all kind of woodland, wooded parkland and pasture etc but they also occur on decaying wood in marshes and wooded wetland situations. Adults have been recorded from decaying bark and wood of a wide range of deciduous trees but birch (Betula L.) and, especially, beech (Fagus L.) seem to be the most frequented species. The species is generally associated with sporocarps and numbers of adults have been found within decaying bodies of Fomes fomentarius (L.) Fr. 1849 but there is an obligate association with various slime moulds (Liceales, Reticulariaceae), on which both adults and larvae are known to feed, and there may be a more specific association with false puffballs (Enteridium lycoperdon (Bull.) M.L. Farr, 1976). Adults are crepuscular and nocturnal and at this time they may be found on the surface of logs and trunks, often in pairs or small numbers, they react quickly when disturbed and will roll into a ball and fall to the ground so it’s best to hold a net to the trunk while searching, but to find them by day it is necessary to search bark and decaying wood, especially on fallen timber in contact with the ground and where moulds are developing. They occur from April until September or October although specimens occasionally occur much earlier, and they peak in abundance during June. Mating occurs in late spring and larvae develop through the summer but it is not known whether winter is passed in the larval or the pupal stage.
Anisotoma orbicularis 1
Anisotoma orbicularis 2
Anisotoma orbicularis 3
© Lech Borowiec
2-3 mm. Broadly elongate and very convex, widest across the basal half of the elytra and continuous in outline, dorsal surface glabrous. The colour is variable but typically shiny black or very dark brown with pale markings; the mouthparts, a spot on the vertex and behind the temples, the pronotal margins and often a diffuse sub-humeral spot. Antennae pale at the base and dark towards the apex, often with segments 7-10 dark and the base plus segment 11 pale. Legs pale or with darkened femora. Head finely punctured throughout, vertex weakly convex, clypeus flattened or slightly concave, eyes large and protruding, occupying most of the lateral margin. Antennomeres 2 & 3 about equal in length club 5-segmented, long and loose with segments7, 9 & 10 transverse and more or less symmetrical and segment 8 diminutive by comparison. Pronotum transverse, broadest across obtuse posterior angles and narrowed to rounded and slightly projecting anterior angles, apical margin curved forward, lateral margin finely bordered and basal margin obliquely angled towards the angles, surface smoothly convex and without structure, sparsely and very finely punctured throughout. Elytra evenly convex, with fine punctures throughout and distinct and regular striae which fade towards the apices and lateral margins, and a sutural stria that extends to the middle. Male tarsi 5-5-4, female tarsi 4-4-4.