Mycetophagus quadripustulatus (Linnaeus, 1761)
This species is native to southern and central Europe extending from North Africa to southern Scandinavia and the U.K. and east to the Caucasus, Iran and eastern Siberia, occurring from lowlands to lower mountain altitudes, and in most countries it is the most common member of the family. In the U.K. it is common across the south becoming more local further north and sporadic and rare in Scotland. Adults are nocturnal and associated with fungal fruiting bodies on decaying timber in woodland, parks and gardens etc., they are active through the spring and early summer but also occur in smaller numbers under bark or logs later in the year and through the winter. During the day they hide under bark or logs etc. or sometimes in the soil beneath logs, and may form aggregations of many specimens, they are active from dusk and may be observed on trunks or logs, especially where there are fungi, through the night and often alongside other saproxylic beetle species. Oviposition occurs in the spring and early summer; the eggs are laid in or near various fungi on a wide range of decaying trees, among the most favoured hosts are freshly expanded specimens with plenty of hyphae and spores of Polyporus squamosus (Huds.), Laetiporus sulphureus ex Fr., Gonoderma applanatum Pers ex Wallr., Pleurotus ostreatus ex Fr., P. ulmarius (Bull.) Fr., and Bjerkandera adusta (Willd. ex Fr), and lamellate fungi are generally ignored. Larvae develop within the fruiting bodies and are fully grown by late July or August, then they will leave the host and pupate some distance away, usually among debris under bark or in soft and decaying wood, but they may descend the trunk or logs and pupate in the soil. Some new generation adults will become active in late summer and remain so through the winter but most will remain hidden and emerge in the spring. Adults are generally slow-moving and easily observed by torchlight but when disturbed may run rapidly or instantly drop to the ground.
Adults are large, 5-6mm, and distinctive due to the elytral markings. The entire dorsal surface is rather densely punctured and clothed in fine and pale recumbent pubescence. Head red and coarsely punctured anteriorly, often partly concealed within the prothorax, eyes transverse and moderately convex, antennae gradually and only weakly thickened towards the apex; segments 6-10 black, otherwise pale. Pronotum transverse and evenly curved from perpendicular posterior angles to a rounded anterior margin, lateral margins distinctly bordered, basal margin bordered and strongly sinuate, surface evenly convex but for the strong basal fovea. Elytra with rounded shoulders, the lateral margins evenly curved to a continuously rounded apex that completely covers the abdomen and each with well-impressed and punctured striae complete to the apex. Legs pale brown; all tibiae with a pair of distinct spurs on the inner apical angle. Male tarsi 3-4-4, female tarsi 4-4-4.
Fully grown larvae are about 8mm long and weakly curved, almost cylindrical or slightly flattened laterally, and pale brown or creamy with the head reddish-brown, the prothorax extensively darkened, and the other body segments with a transverse dark band along the anterior margin, giving a striated appearance. The prothorax is quadrate, all other segments are transverse and the whole body is clothed with sparse short and erect setae. The Mesothorax and abdominal segments 1-8 have obvious annular spiracles, and the ninth has a pair of relatively long and upturned; hook-like and sharp, urogomphi. The legs are robust and relatively long, with setae as on the body, and each has a singly strongly-curved claw. They will generally be found in numbers among fungal tissue and will often be carrying mites.