Tetratoma fungorum Fabricius, 1790
Although widespread in Europe this Western Palaearctic species is generally rare and local and thought to be in decline through much of its range, in southern and central Europe it can be locally common but further north, where it extends to the southern provinces of Fennoscandia, it is very local and rare which is perhaps surprising since it is locally common across southern England and Wales, though mostly absent from the West Country, and more local but still widespread to the Scottish borders. All stages are associated with various tree fungi upon which they feed; a wide range of hosts have been recorded but, at least in the UK, it is associated primarily with the birch bracket fungus, Polyporus betulinus (Bull) Fr. and the beetles life-cycle is generally synchronized with the appearance of its fruiting bodies; adults appear in the autumn and soon find their fungal hosts, they oviposit in bark crevices and the tiny larvae find their way to the fungus and bore into it to begin feeding. Larvae feed and develop through the winter and at this time mortality may be high as there are usually high densities of first instars in the autumn compared with later instars through the winter, they may be present for several seasons on a single tree, colonizing fresh fungi as well as old and dry specimens, they generally only infest fungi low down on the tree, typically from two to four metres, and any fungus higher or lower than this is unlikely to be used as host material for the larvae. Larvae are fully-grown by the spring when the fungi generally die-off and dry out, at this time they make their way down the trunk and enter the ground to pupate in a cell a few centimetres below the surface. Adults are present year-round, the new generation eclose in the spring and are active nocturnally, feeding on various fungi and remaining under bark or in the soil beneath trunks during the day, they mate towards the end of the summer and oviposit in the autumn. The best way to find adults is by searching at night by torchlight but they will often be found under bark on a wide range of broadleaf trees e.g. we have found them in large numbers under horse chestnut and oak bark in a local park and they often turn up in samples taken from debris under loose bark. Among other fungi recorded as hosts are Polyporus squamosus (Huds.) Ex Fr., Laetiporus sulphureus (Bull. Ex. Fr.) Murr, Pholiota adipose Fr., and P. aurivella (Batsch ex Fr.) Quél. and adults have been recorded from Armillaria mallea (Vahl) P. Kumm, (on spruce), Pleurotus astreatus (Jacq. Ex Fr.) P. Kumm and a species of Stereum Hill ex Pers.
Adults are readily recognized by the small size and distinctive bicoloured appearance, they are superficially similar to members of the erotylid genus Triplax-a classic example of convergence as both are nocturnal saproxylic fungivores- but Triplax are most easily recognized by the regularly striate elytra. 4.0-4.5mm. Dorsal surface shiny; head and antennal club black, elytra metallic blue, otherwise entirely pale brown to orange. Head narrowly visible from above, vertex flattened and finely punctured, eyes convex and relatively large, antennae inserted laterally in front of the eyes; 11-segmented with a long and loose four-segmented club. Pronotum widely transverse and moderately convex, with a pair of variously impressed basal fovea, diffusely and rather strongly punctured throughout, lateral margins rounded and widest a little behind the middle, angles rounded and basal margin sinuate and weakly produced across the middle. Elytra long and weakly broadened to a continuously-rounded apex, surface randomly and quite densely punctured although these may become finer or even absent towards the apex, without any trace of punctured striae but there may be a longitudinal impression beneath the shoulders and another beside the suture towards the apex. Legs long and slender, femora and tibiae unarmed and finely pubescent, tibial spurs tiny. Tarsi 5-5-4 and slender, without any bilobed segments.
Generally smaller (2.5-4.5mm)
Elytra with punctured striae
3-segmented anntenal club
Pronotal margins straight