Tetratoma ancora Fabricius, 1790
Present throughout the entire northern Palaearctic region, this species occurs locally across Europe from the Pyrenees to the Balkan Peninsula and north to the UK and above the Arctic Circle in Fennoscandia, it occurs from lowlands to about 2000m and in many northern countries is most frequent in mountainous areas although as with many saproxylic species there has been a general decline over recent decades. It is widespread but very local across mainland UK and the north of Ireland but absent from much of the English midlands as well as Hampshire and Dorset, it is frequently recorded only from the south east below London and there has been a recent decline, but the species may be under recorded as it is difficult to find and adults seem to lead a very secluded life e.g. we have recorded it only once from our local park in more than 10 years of sampling. The usual habitat is old broadleaf woodland and wooded parkland with plenty of old trees in various stages of decay, adults occur on a range of broadleaf trees but particularly oak and beech and sometimes among logs and piles of brushwood, they are nocturnal and usually occur in small numbers, often among numbers of superficially similar mycetophagids and often among deeply fissured bark and so need to be looked for very carefully, they occur over a long season but are most prolific from June until August, and they disperse by flight. Larvae develop among fruiting bodies of various fungi, in the UK they are recorded from Phlebia merismoides (Fr.) Fr. 1818, usually on dead oak branches, (but they probably occur on other fungi) and on the continent also from species of Stereum Hill ex Pers. (1794), Fomes fomentarius (L.) Fr. 1849, Phellinus tremulae (Bondartsev) Bondartsev & Borisov, P.N.(1953), Bjerkandera adusta (Willd.) P. Karst (1880) and Piptoporus betulina (Bull.) Cui, Han & Dai (2016), from a range of broadleaf trees including hornbeam, beech, alder, birch, oak and poplar and, more rarely, from several conifers including pine and spruce. Fully-grown larvae are thought to leave the host and enter the ground to pupate in the autumn (although other species of the genus are known to overwinter as larvae) and the resulting adults, which may become active late in the year, overwinter and appear in late April or May.
3.0-3.5mm. Elongate and broadly oval, head brown, usually paler anteriorly, pronotum dark grey with pale borders, elytra bicoloured dark grey or black and pale brown and distinctively patterned; the brown markings can form discrete maculae at the shoulders and in the basal and apical thirds but they are usually much more extensive and are often united, in any case a certain identification can be made by comparison with good pictures. Antennae pale with the larger segments (at least) darkened, legs pale brown but sometimes darkened towards the femoral and tibial apices. Upper surface with moderately dense punctures and short pale pubescence. Two basal antennomeres broadly expanded, 3-6 narrow in contrast to 7-11 which form a loose club. Pronotum transverse and broadest about the middle, curved, irregular and narrowly explanate laterally and smoothly convex or indistinctly depressed in front of the basal margin. Elytra smoothly curved from distinct humeral angles to a continuously-rounded apical margin, without striae but randomly punctured throughout, these becoming finer towards the apex. Legs long and slender, tibiae smooth and only weakly expanded towards truncate apices and with very fine and short terminal spurs. Tarsi 5-5-4, the basal segments of the front and middle tarsi weakly lobed ventrally, claws smooth and without a distinct basal tooth.
A very distinctive species but superficially similar to some mycetophagids e.g. Mycetophagus piceus, M. multipunctatus or Litargus connexus, a careful comparison of the elytral pattern (etc) is usually sufficient to distinguish the present species but if in doubt the tarsal formula will separate the groups.