Mycetophagus atomarius (Fabricius, 1787)
This generally common western Palaearctic species occurs throughout Europe from Spain north to above the Arctic Circle in Fennoscandia and south to the Mediterranean but is absent from many of the islands and from North Africa; in the north it is locally common and often abundant whereas in many southern areas it is more prolific in upland and low mountain areas, it is locally common across Wales and the south of England and more sporadic and scarce further north into the south of Scotland. Typical habitats are open deciduous woodland and wooded parkland but they also occur on suitable isolated trees in gardens or on roadsides etc, adults are associated with fungi on a range of broadleaved trees but more particularly with Hypoxylon fragiform (Pers.) J. Kickx on dead beech (Fagus), and Daldinia concentrica (Bolton) on ash (Fraxinus), other fungi listed as hosting the species are Kretzschmaria deusta (Hoffm.), Ganoderma applanatum (Pers.), Pleurotus ostreatus (Jacq. Ex Fr.) and Pluteus cervinus Schäffer : Fr), all of which occur on a range of broadleaved trees. Adults are present year-round and active from March or April until the autumn, they are nocturnal and often appear in numbers on the surface of logs and trunks in the vicinity of their host fungi, they may be very active but soon vanish into bark crevices or cracks in exposed wood when disturbed; examining or sieving suitable fruiting bodies may reveal them at any time and they usually appear among numbers of other beetles including other species of Mycetophagus. Adult numbers peak in spring and autumn; little is known of their biology but breeding is thought to occur in spring and early summer, larvae live within fruiting bodies and are known to feed directly on mycelium and fungal tissue, and pupae have been found under bark in late summer.
4.0-4.5mm. Adults are easily recognized by the elytral pattern and the form of the antennae, the only species with which it is likely to be confused is M. multipunctatus (Fabricius, 1792) (see below). Upper surface finely pubescent, head and pronotum dark brown, elytra a little lighter and with distinctive pale markings, legs pale brown, antennae pale with (usually) segments 6 or 7 to 10 darker. Head transverse and only narrowly visible from above; smoothly convex and rather densely punctured throughout, with small and weakly convex eyes and densely pubescent frons and clypeus. Antennae inserted laterally in front of the eyes, basal segment much broader than the following, 2-5 elongate and narrow, and 6-11 forming a gradual club with segments 9-11 distinctly transverse and the terminal segment much shorter than 9+10 combined. Pronotum widely transverse, broadest in the basal third and rounded to a curved anterior margin, the anterior angles hardly visible from above and the basal margin sinuate either side of the middle. Surface of pronotum finely wrinkled, the punctation dense and of two types, large and very fine, and with two deep fovea towards the base. Elytra elongate (about 1.5:1) and slightly narrower than the base of the pronotum, lateral margins weakly curved to a continuously rounded apical margin, striae finely impressed and punctured to the apex, interstices slightly convex, for the most part weakly transversely wrinkled and finely and densely punctured, the pubescence curved and semi-erect. The elytral pattern varies a little, especially in the strength and number of the spots about the middle, but is usually distinctive enough to identify the species, the foremost discal spot may be joined to the angled humeral marking and the subapical marking may vary in size but the transverse zigzagged marking in the apical third is distinctive. Legs long and slender, femora only narrowly visible from above, tibiae narrow and with only tiny apical spurs, tarsi 4-segmented in the female, 3,4,4 in the male, the basal meta-tarsomere longer than the terminal segment.
Antennal club more distinctly differentiated
Pronotum broadest about the middle and narrowed to the base and apex
Elytral markings more extensive, especially laterally
Basal and terminal tarsomeres equal in length