Atrecus affinis (Paykull, 1789)

Widely referred to in the literature as Baptolinus (Joy, Fowler, Freude). A locally common species found throughout Britain with records from the very north of Scotland (NBN). Associated with a wide range of trees in various stages of decomposition, we have recorded them from woodland and parkland across Watford. They occasionally turn up in samples of decaying heartwood, both damp and compacted or open and powdery dry, but are most often encountered under bark. In whippendell wood they occur under areas of damaged and resinous pine both standing and fallen as well as under the dry and loose bark of stacked pine logs. Also under bark of Pruneus, Arium, Quercus, Fagus, Carpinus and Fraxinus and sometimes on the wood surface in contact with the soil/ground. They are occasionally extracted from fungus samples but these are almost certainly adventitious as the majority of adults observed in the field are not obviously associated with fungi. Perhaps the easiest way to observe Atrecus is to look under bark covered with a deep layer of soil or plant debris and moss. During summer, autumn and winter we find them either singly or just as often pairs, during the spring we have several times found small congregations between six and twelve specimens.

An 'easy' species to identify even in the field, its size and colouration being distinctive. See Othiini in the ID Aids section.

The following description is based on 7 local specimens examined at X20.
6-7.5mm. Head shiny and black (microsculpture obvious at X50), slightly elongate, with mandibles characteristically shaped, with 4 setose punctures on disc behind eyes; 2 close to inner margin and 2 on clypeus. 4 punctures on disc behind eyes and several around lateral and hind margin, their long setae being obvious. Eyes small, more or less circular when viewed from the side. Temples long, hind angles smoothly rounded to a narrow neck. Clypeus deeple emarginate. Palpi long with pointed terminal segment. Antennae red, sometimes darkened apically, with scape as long as next two segments, segments 2,3 and 11 elongate, 4 and 5 quadrate and 8-10 transverse, inserted within base of mandibles. Clypeus longitudinally furrowed behind antennal insertions to front margin of eyes. Pronotum shining red, usually darker laterally, finely bordered all round. Hind angles rounded, front angles obtuse when viewed from above. With 4 large punctures; 2 on disc and 2 behind front margin and several weaker ones laterally and basally, their long setae obvious. Elytra shining black with base and humeri red, weakly rugose and finely punctured with a few scattered larger ones. Sutural margins slightly overlapping and strongly bordered, hind margin sinuate and with obvious lateral setae. Scutellum equilateral, shining and impunctate. Abdomen red with segments 4 and 5 to some extent dark. Segments sparsely punctate and pubescent except on disc, each with a long setae laterally before hind angles. Side borders strongly raised. Legs red, all tibiae with a strong terminal spine on inner side, mid tibiae with strong spines along outer edge, hind tibiae with spines on outer side beyond middle. Front tibiae dilated beyond middle. Protarsal segments dilated, in some specimens much more so than in others (dimorphism?).