Triplax aenea (Schaller, 1783)

This is a rather sporadic European species, it extends from Spain into parts of European Russia and to the north of Fennoscandia although it is absent from Finland, Asia Minor and much of the Balkan Peninsula, in southern regions it extends to higher mountain altitudes but it is otherwise a typical lowland species. Through much of central Europe it is the most common member of the genus and it can be locally common or even abundant but, especially in the north, is absent or rare in many areas, it is generally common throughout England and Wales and there are isolated records further north to the Scottish Highlands. Typical habitats are deciduous woodland and wooded parkland and pasture where it is associated with fungus-infested wood on a wide variety of trees including Oak, Horse Chestnut, willows, poplars, elms and various fruit trees; in northern regions mostly on birches and aspen and in northern Europe sometimes on various conifers. Adults occur year-round; they overwinter under bark or among decaying wood on trunks and stumps and become active from March or April and remain so until the autumn, they are nocturnal and may be found on stumps and trunks etc. usually among or near to developing sporocarps upon which they feed, mating occurs in spring and early summer and females oviposit directly into fungi or among crevices beneath fruiting bodies. The mycophagous larvae have been recorded from a wide range of fungi but occur most frequently from Tinder fungus (Fomes fomentarius (L.) Fr, 1849) and Oyster mushrooms (Pleurotus (Fr.) P. Kumm. 1871), and they can be abundant on Chicken-of-the-woods (Laetiporus sulphureus (Bull.) Murrill (1920)), they develop through the summer, pupate among host material or in decaying wood below and new-generation adults occur in the summer and autumn but it is not known whether there is a second generation. Searching at night may reveal adults on bark or fungi although they tend to be photophobic and so careful searching may be needed, they hide among fungi or bark during the day but are easy to find due to their bright colours, and they often occur among extraction samples through the winter.

3.3-4.5 mm. Elongate-oval and almost continuous in outline, forebody, scutellum and underside orange, elytra metallic blue or, rarely, black with only a slight bluish tint, legs and palps orange, antennae black. Head transverse with convex and prominent eyes and short temples, surface evenly convex and finely punctured. Terminal maxillary palpomere widely securiform, antennomeres 9-11 form an elongate and loose club. Pronotum transverse, broadest at perpendicular posterior angles and narrowed to slightly protruding anterior angles, apical margin curved forward, basal margin sinuate and finely grooved, surface vaguely depressed either side at the base, otherwise rather flat, punctures strong and well separated. Elytra long and gently curved from sharply-angled shoulders to a continuous apical margin, basal margin sinuate and strongly punctured to finely-toothed shoulders, surface with distinct punctured striae that fade just before the apex, interstices flat and very finely punctured. All coxae widely separated, femora flattened and expanded about the middle, tibiae straight, only weakly expanded to obliquely-truncate apices and without obvious terminal spurs. Tarsi 5-segmented but appearing 4-segmented as the small fourth segment is mostly hidden within the bilobed third segment.

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Distinguished among our UK members of the genus by the finely bordered pronotal base, blue elytra and entirely pale underside, the only likely confusion, especially in the field, might be with Tetratoma fungorum Fabricius, 1790, but here the elytra are strongly and randomly punctured.