Atheta castanoptera (Mannerheim, 1830)
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POLYPHAGA Emery, 1886
STAPHYLINOIDEA Latreille, 1802
ALEOCHARINAE Fleming, 1821
ATHETINI Casey, 1910
Atheta Thomson, C.G., 1858
Dealing with members of the Athetini can be very difficult because the nomenclature has changed frequently over the years and there has never been a satisfactory work in English dealing with the identification or synonymy. This has recently changed with the publication of our latest checklist, although the inclusion of such a wide assemblage of species in the present genus is not followed generally and so as ever this is also likely to change in the future but for now it provides a good reference point and enough useful synonymy etc to be good for finding out which species we are dealing with when using other works. The present species has been subject to the usual shuffling around between genera etc. and may be found in the older literature under the following names: Bolitochara castanoptera Mannerheim, 1830, Aleochara. xanthoptera Stephens, 1832, A. consobrina Stephens, 1832, A. foveatocollis Stephens, 1832, Homalota pertyi Heer, 1839 and H. merdaria Thomson, 1852. Another difficulty has been with identification as these beetles are very difficult to diagnose using external morphology, as anybody having tried Joy’s Handbook without reference material will know, but the present species has very distinct genitalia and so can be identified and named with certainty.
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This is a very widespread Palaearctic species; it occurs throughout Europe and extends east through Russia and Asia Minor into eastern Siberia and North Korea, it is widespread across North Africa, Iran and Syria and is present on the Atlantic Islands, in Europe it occurs sporadically from Portugal to the Balkans and north to the UK and some northern provinces of Fennoscandia although it has only recently been identified from Finland, it is locally common throughout but seems to be much more frequent in the north. Here it is locally common and often abundant throughout Wales and England north to Yorkshire and sporadic and rare further north to southern Scotland and there are records from Skye and Northern Ireland. Adults occur year-round; they are common through the winter and peak in abundance during early spring and autumn but are seldom found in numbers during the warmer months. The species is nocturnal and almost always associated with damp decaying sporocarps, the type of fungus seems to be less important than the extent of
decay and so adults should be expected among any decaying fruiting bodies, both arboreal and terrestrial. We have found adults in great abundance during the autumn in our local park among large and well-decayed terrestrial fruiting bodies that have slumped onto the ground and become waterlogged, disturbing the fungus exposes large numbers of adults and the aromatics released soon attract many more which at times swarm around in numbers. They appear in suitable extraction samples through the winter and may appear in huge numbers again in early spring; we found them among a large array of wet and well-decayed Laetiporus that had fallen to the ground beneath an oak trunk during the winter, and they were also present among the fungus still attached to the tree. It is highly unlikely that specimens will be identified in the field as they generally occur among numbers of closely similar species and so specimens will need to be taken for dissection, but upon examination they will become familiar and different species will eventually become distinctive if enough samples are examined, an advantage of taking numbers of adults is that males can be verified by pressing down on the abdomen to extrude the genitalia which are instantly recognizable, likewise females soon become familiar by association. Adults do occur through the summer but usually in small numbers although they can occasionally be common about decaying fungi in damp and shaded woodland habitats, they may be disturbed and collected during the day but they are very agile and tend to vanish into the soil or take flight, by night much larger numbers may be found and they tend to remain among the fungi and oblivious to light when disturbed.
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​3.6-4.2 mm. Elongate, slender and discontinuous in outline, forebody dark brown or black, sometimes faintly metallic, elytra brown but variably darkened around the scutellum and posterior angles, abdomen shiny black or with the apical margins of the tergites pale, legs pale brown, antennae dark brown with three or four basal segments and the apical segment pale. Head transverse and produced between large and convex eyes, temples evenly curved and about as long as the eyes, surface evenly convex, finely punctured and pubescent and with very fine cellular microsculpture. Penultimate maxillary palpomere long and broadened from the base, terminal segment diminutive. The long and slender antennae are a good guide to the species; segments 1-3 very elongate, 4-7 elongate to quadrate, and 8-10 slightly transverse, the terminal segment gradually narrowed to a rounded apex and longer than 9 & 10 combined. Pronotum transverse, about 1.3:1, broadest in front of the middle and almost evenly rounded from obtuse posterior angles, lateral margins with several outstanding small and stiff setae, surface rather flattened and with a variable median impression before the base, finely punctured and pubescent; the hairs lying transversely and forming an arcuate pattern either side of the mid-line, microsculpture extremely fine. Elytra distinctly wider than the pronotum, with rounded shoulders and sinuate apical margin, length along the suture about equal to the length of the pronotum, punctures and microsculpture similar to the pronotum, pubescence for the most part forming wavy longitudinal lines. Abdomen long and only weakly expanded about the middle, often almost parallel-sided in the basal half, tergites with extremely fine transverse cellular microsculpture, basal tergites impressed across the base and sparsely punctured and pubescent, apical tergites with very fine lines across the base but not impressed, the surface almost glabrous. Males may be recognized by the finely-toothed apical margin of the sixth tergite. Legs long and slender with robust femora widely visible in normal setting, tibiae finely pubescent throughout, the front tibiae with at least one larger outstanding seta about the middle, the middle tibiae with two larger setae on the outer margin; one near the base and one about the middle, hind tibiae without larger outstanding setae. Tarsi 4-5-5 (extremely difficult to count), all segments simple, claws smooth and without a basal tooth. The above should give a good impression of the species which, with a little practice, can be identified on sight but reference material should be prepared with the genitalia dissected out as these are very distinctive in both sexes and should not be confused with any other species.