Atrecus affinis (Paykull, 1789)
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POLYPHAGA Emery, 1886
STAPHYLINOIDEA Latreille, 1802
OTHIINI Thomson, C.G., 1859
Atrecus Jacquelin du Val, 1856
This widespread Palaearctic species is the only member of the genus to occur in the U.K., it is generally common in suitable habitats throughout Europe, extending into Turkey, Iran and eastern Siberia, and here it occurs throughout; to the far north of Scotland. The typical habitat is mature woodland and wooded parkland etc. where there is plenty of wood in an advanced state of decay; both larvae and adults occur under loose bark on the trunks and fallen timber of a wide range of deciduous and coniferous trees, they often occur in damp conditions under old bark covered in moss and litter, or where grass etc. is growing over old logs. We have recorded them from birch, beech-several times from logs on calcareous grassland, oak, pine and fir. Adults are occasionally present in extractions of saproxylic fungus but they do not appear to be closely associated with fungi in the wild. In South Hertfordshire we have recorded them throughout the year; during the spring often in small aggregations and sometimes in cop. but otherwise as pairs or single specimens, and we have yet to find them active nocturnally. This very distinctive species is readily recognized in the field by the characteristically coloured body and pale appendages, the only confusion might be with various Othius but here the abdomen is uniformly coloured and the mandibles are not so produced.
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6-7.5mm. Head slightly transverse, shiny black with strong linear microsculpture that is obvious at X40, characteristic long, straight-sided mandibles and small, weakly convex and circular eyes. The clypeus has a single longitudinal furrow behind each antennal insertion and the labrum is narrow and deeply emarginate. The surface has scattered micropunctures and a distinctive pattern of larger setiferous punctures; 4 behind each eye and 4 in a transverse row across the vertex from the centre of the eyes. The temples are long, rounded and narrowing to a wide and swollen neck. Antennae inserted dorsally between the outer margins of the mandibles, the basal segment as long as the next 2, and the rest becoming gradually wider towards the apex. The palps are long and slender with the terminal segment pointed. Pronotum elongate and slightly narrower than the head, red although often darker laterally, the surface with linear microsculpture and 4 large punctures; 2 near the anterior margin and 2 near the middle, and finely bordered throughout. Elytra shiny black with the base red, weakly rugose and finely punctured but without microsculpture, the sutural slightly overlapping and strongly bordered. Abdomen strongly bordered, red with segments 4 and 5 darker, sparsely punctured and pubescent, and each segment with a long seta before the hind angles. The legs are robust and long, all tibiae with a strong spine on the inner apical angle, meso-tibiae with strong spines along the outer edge and the meta-tibiae with similar spines towards the apex. Pro-tarsal segments dilated, more so in the male.
Atrecus Jacquelin du Val, 1856
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Formerly constituting the type genus of the Atrecini Jacquelin du Val, 1856, Atrecus is now classified as a genus of the Othiini Thomson, C.G., 1859 and includes 14 species. The type species A. pilicornis (Paykull, 1790) is Holarctic, and 2 species are widespread throughout the Palaearctic; A. longiceps (Fauvel, 1873) and A. affinis (Paykull, 1789), the latter of which is the only U.K. representative. Several are more restricted e.g. A. ardeanus Cicerai, 1990 from Italy, A. casalei (Bordoni, 1987) from Greece, and A. parvioculatus Assing, 1998 from Turkey. A. brevicornis Smetana, 1967 is a widespread Asian species while two recent additions are restricted to China; A. schuelkei Assing, 1998 from Szechwan Provence, and A. yunnanus Assing, 2000 from Yunnan Provence. Of the Nearctic species 2 occur in the United States: A. newtoni Smetana, 1982 and A. punctiventris Fall, 1901, while a further 3 occur in the U.S. and Canada: A. americanus Casey, 1906, A. macrocephalus Nordmann, 1837 and A. quadripennis Casey, 1906.
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All are medium sized staphs, 6-10mm, and characterized by the long, straight-sided mandibles which when at rest form a long triangle in front of the head. They are shiny, rather flattened and parallel-sided species varying from entirely dark e.g. in macrocephalus to characteristically coloured with the head, elytra and some abdominal segments dark and the pronotum and some abdominal segments orange to red, as in affinis. A. macrocephalus is unusual; entirely pale with the head dark and the elytra bicoloured. In all species the appendages are pale. Immature specimens are entirely pale. The head is quadrate to transverse and wider than the pronotum, very much so in macrocephalus, shiny and variously microsculptured and with scattered large punctures and long sensory setae. The eyes are generally small and convex, the temples long, parallel and rounded at the base and the vertex weakly convex to rather flat. Clypeus emarginate, often deeply so, the mandibles long and sharp; straight along the outer edge and incurved at the apex, variously toothed along the inner margin but usually with a large tooth towards the apex. The terminal segment of the maxillary palps is pointed and as long as the penultimate. Antennae inserted inside the outer margin of the mandibles, closer together than to the corresponding eye; 11-segmented, the basal segment long and weakly curved, 2-5 quadrate to weakly transverse, 6-10 strongly transverse, and the terminal segment is narrowed to a rounded apex. The neck is wide and sparsely punctured, ventrally with a pair of small plates anterior to the prosternum. Pronotum sub-parallel and elongate, the lateral border complete to the anterior angles and the surface microsculptured and bearing a few large punctures, some of which are situated in the posterior half. Elytra smooth and usually lacking microsculpture, the surface generally wrinkled to some extent e.g. barely so in affinis, and often very strongly so in pilicornis, usually with rounded and well-developed shoulders, the suture is bordered, not overlapping and sometimes diverging at the middle, and the hind margins truncate and sinuate. Abdominal tergites transverse with strongly raised borders, the surface generally wrinkled, sparsely punctured and with 2 transverse raised lines towards the base. The legs are long and robust; the femora without teeth or spines, the tibiae long and gradually widened towards the apex, and each with strong spines along the outer margin and a pair of spines at the inner apical angle. Tarsi 5-5-5, pro-tarsal segments 1-4 dilated in both sexes, the meso- and metatarsi without bilobed segments.
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All species are saproxylic, occurring on both coniferous and deciduous trees although some may be confined to conifers. The Nearctic A. americanus is occasionally found among vegetation and litter or under debris on river margins. Some e.g. are generally associated with polypores and some are known to be predators of scolytid eggs and young larvae, the adults occurring in the galleries. A. affinis is common in rice fields in Northern Iran. In general they occur on decaying fallen timber with loose bark, and it seems they are more frequently recorded from conifers.