Triplax aenea (Schaller, 1783)
Widely distributed with records as far north as Easter Ross, many records from the midlands and south east, scattered elsewhere. Very common around Watford, appearing wherever large fungal fruiting bodies are found on trees , usually soon after the fungus opens. First specimens appear during May and soon they are found in numbers, individual fungi harbouring dozens, often in company with large numbers of Mycetophagus quadripustulatus L. Occasionally found as single specimens under bark among fungal growth, here every specimen should be carefully examined as they superficially resemble Tetratoma fungorum Fab., but this species has dense and random deep puncturation on the elytra. We have never found aenea during the winter although dead adults are occasionally found under bark in the autumn.

2.5-4.5mm. Elongate with clubbed antennae, red pronotum and brightly metallic blue elytra this species is only likely to be confused with Tetratoma. Antennae black, eleven segmented with loose three segmented club. Head and pronotum finely punctured, red although head often darker. Pronotum finely bordered laterally and basally, with front angles produced. Scutellum red, as pronotum. Elytra entire with complete punctate striae, humeral prominence outside 5th stria obvious. Underside and legs completely red. Tarsal segments 1-3 broadened, 3 strongly bilobed, 4 very small, 5 elongate.

Usually on the fungus Pleurotus ostreatus fruiting on trunks of trees (Alexander)
In our experience from fungus on Fagus and Aesculus, under bark of Fagus and Quercus.

Description from 4 Watford specimens at X20