Prionychus Solier, 1835
This small genus includes 10 species and is restricted to the Western Palaearctic region, six species occur in Europe but only two (see below) are widespread, the others being very local and generally rare; P. fairmairei (Reich, 1860) is endemic to Italy, P. cisteloides Seidlitz, 1896 to Germany, P. lugens Kuster, 1850 is known only from Sicily, and P. striatipennis Pic, 1909 is known from Bulgaria and Romania, with a single record from each. The two widespread species extend to the UK where they are very unlikely to be confused with any other species except for each other but they are easily separated as follows:
Larger species, 12-14mm. Elytra and pronotum rather dull, with fine but distinct granular microsculpture, anterior pronotal margin unevenly curved, sometimes straight in the middle. Appendages usually evenly black or dark reddish-brown.
Smaller species, 10-12.5mm. Elytra and pronotum shiny, with at most indistinct microsculpture, anterior pronotal margin evenly curved. Appendages usually lighter, often with the tarsi lighter reddish.
They are medium-sized and entirely black beetles, often with a faint metallic blue or green lustre, they are broadly-oval, rather parallel-sided and discontinuous in outline, and the dorsal surface is clothed with inconspicuous short recumbent or semi-erect dark pubescence. The head is transverse and rounded anteriorly, with transverse, convex and emarginate eyes and short bulging temples, the punctation is fine and diffuse and the clypeus is transversely impressed. The terminal maxillary palpomere is securiform and the antennae are relatively short; the insertions are hidden from above and all segments, except the short second segment, are elongate, the third and fourth being longer than the others. The pronotum is widely transverse, broadest near
Prionychus ater 1
Prionychus melanarius 1
© Lech Borowiec
Prionychus ater 2
Prionychus ater 3
Prionychus ater 4
Prionychus ater 5
the base and narrowed and evenly rounded anteriorly, almost semi-circular, the surface is finely and moderately-densely punctured, the punctures separated by about their own width, and evenly convex but for oblique and shallow basal fovea, basal margin sinuate and variously bordered. Scutellum small, triangular and very finely punctured and pubescent. Elytra slightly narrower across the base than the base of the pronotum, with rounded shoulders, slightly curved lateral margins and a continuously-curved apical margin, surface with well-impressed striae, including an abbreviated scutellary striole which are finely punctured, as the adjacent interstices. Legs narrow and moderately long, femora unarmed and visible from above with normal setting, tibiae narrow to the apex, each with two small terminal spines. Tarsi 5-5-4, without expand segments; pro-tarsomeres 1-4 about equal in length, the terminal segment longer, basal segment of middle tarsi slightly shorter than the terminal segment, basal segment of hind tarsi as long as the others combined, penultimate segment of all tarsi with ventral lobes.
Prionychus ater (Fabricius, 1775)
This species is locally common across Europe from France to Romania and Greece, extending east into Ukraine and Russia as far as the Caspian Sea and north to the south of Fennoscandia, it is present in Italy but otherwise largely absent from Mediterranean regions. Here it is locally common across Wales and England north to Nottingham although sporadic and rare in the southwest. The typical habitat is woodland and wooded parkland with a good supply of deciduous trees in various stages of growth and decay, here it is a most lowland species but on the continent extends to the tree line in mountain areas. Adults are active over a short season, generally from June until August or a little later, they are nocturnal and may be observed on warm nights on the surface of decaying standing and fallen timber, mostly a wide range of deciduous trees but they have also been recorded from various conifers on the continent, they are otherwise difficult to record as they spend most of their time under loose powdery bark or in deep crevices or among accumulated wood and debris in hollows. They tend to remain on their host material and large populations may build up over several years; in a local park they have been abundant over many years on a large dead and powdery-dry lime tree devoid of bark and infested with Dorcus and Sinodendron etc, and on warm evenings they can be seen on the trunk from ground level up to about seven meters among the branches, but they otherwise appear only rarely on the many apparently suitable nearby trees. Larvae inhabit decaying wood infested with moulds and wood-destroying fungi in hollows, often beneath avian nests, or among accumulated debris under loose bark, they develop through the summer and following winter and pupation probably occurs in the spring as larvae have been recorded from January to March on the continent. Adults must be looked for carefully and may be difficult to observe by torchlight as they will often drop to the ground or retreat into the wood when illuminated but they are large and distinctive and so easily spotted, they will soon become familiar and might only be confused with our other member of the genus.
Prionychus melanarius (Germar, 1813)
This is a much more local and rare species; it has a mostly south-eastern and central European distribution extending south to northern Italy and north to southern Fennoscandia and the UK, it is more frequent in the south of this range but seems to be common only in relict old deciduous woodland. Here it is a very local and rare species with only a few widely scattered records, mostly in the south and near the coast; West Sussex, the Severn Valley and Suffolk and there is a single record from Nottinghamshire. Adults are nocturnal and usually recorded on trunks of a wide range of deciduous trees, especially ash, oak, alder, willow and beech, and more rarely on pine, spruce and larch, and are active over a short season during July and August. Larvae develop among wood debris etc. in hollows at the base of trunks and branches or under bark, they grow through the winter and spring, feeding on decayed wood and frass and pupate in late June or July. The adults appear from mid-July and are short-lived, rarely surviving beyond August.