Microrhagus pygmaeus (Fabricius, 1792)
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POLYPHAGA Emery, 1886
ELATEROIDEA Leach, 1815
MELASINAE Fleming, 1821
DIRHAGINI Reitter, 1911
Microrhagus Dejean, 1833
This is a mostly central and northern European species; it extends sporadically south to the Mediterranean and has been recorded from Morocco, but it tends to be rare and very local in warmer regions, it otherwise occurs from Portugal to Ukraine and north the UK and southern Fennoscandia, it is locally common in some central areas e.g. in Germany and Denmark but is otherwise sporadic, being rare in Poland and the other Baltic countries. In the UK it is very local across the south and south-west of England north to London and across southern Wales and the west midlands although it is likely to be under-recorded and it seems to have become more common in recent decades. Typical habitats are established deciduous woodland or wooded parkland with plenty of wood in various stages of decay, and it is probably the case that in the UK they are most often recorded from old oak woodland. Adults are active from late May until early August although they have been recorded in small numbers from extraction samples etc throughout the autumn and winter, they are mostly nocturnal but also become active on hot summer afternoons when they may be found running in numbers on trunks and fallen timber. They can be difficult to observe as they tend to run into cracks and crevices when disturbed but removing bark or sieving through subcortical debris will often reveal them, they fly in the evening and at night and are often recorded from flight-interception (sticky) traps placed close to trunks or logs but the easiest way to see them is at night by torchlight. Mating occurs from late spring and the mycophagous larvae are known to develop through the summer under bark or among decaying wood, often where this is invaded by hyphae; they have been recorded from a wide range of broadleaved trees including ash, oak, beech, alder, birch, poplar, rowan, hazel and, on the continent, also from spruce. Larvae generally occur among decaying xylem in larger branches, often in shaded situations, they overwinter and complete their development in the spring, pupating under bark or among soft decaying wood in March and April.
3.5-6.0 mm. Elongate and fusiform, entirely black or with the elytra dark chestnut-brown, legs paler reddish-brown with yellow tarsi, antennae dark grey. Very similar to various elaterids but distinguished by the antennae; the first segment is much longer than the distance between the insertions, and the second segment is inserted laterally at the apex of the third. Head hypognathous and only narrowly visible from above, eyes weakly convex and with tiny facets, vertex and frons evenly and weakly convex and with fine punctures and pubescence except for a smooth centre-line. Antennae inserted in the anterior margin, with a long and curved basal segment and a small second segment in both sexes, otherwise dimorphic; in the male strongly pectinate and in the female serrate. Pronotum transverse; broadest at sharp and strongly-produced posterior angles and evenly curved to the anterior margin, surface with a variable longitudinal median impression and a wide and shallow depression either side of the disc, punctures wide, shallow and discrete, fresh specimens have quite dense pale pubescence but this is quickly lost. Scutellum large, triangular and densely pubescent about the apex. Elytra as broad across rounded shoulders as the distance between the pronotal hind angles, almost straight laterally and evenly narrowed to a continuously-rounded apical margin, surface randomly punctured throughout, towards the lateral margins often appearing quite strongly cross-rugose, without striae but with complete or partial and rather random longitudinal impressions that may extend to the apex, entire surface with short pale pubescence. Legs long and slender, tibiae without teeth or apical spurs. Tarsi 5-segmented although the front tarsi may appear 4-segmented due to the tiny fourth segment, basal segment of the middle and hind tarsi very long.