Platystethus alutaceus Thomson, 1861
This very widespread Palaearctic species occurs from lowlands to about 1000m throughout Europe, extending north into Fennoscandia and the UK, and east through Asia Minor, Ukraine and Mongolia to the far east of Russia although it is absent from china, to the south it occurs across North Africa and is present on the Canary Isles. Through much of this range it is locally common but in the north it becomes more sporadic and rare e.g. it is classed as threatened on the Finnish Red List, in the UK it is widespread but very local across England and Wales and rare further north to southern Scotland; it is most frequent in the southeast of England and only rarely recorded from the southwest. Here the typical habitat is among patchy vegetation in marshy areas or on permanently wet soil beside ponds and rivers but on the continent they occur in damp situations more generally e.g. roadsides, damp woodland and arable land, and they often occur in disturbed sites and on damp compacted soil. Adults occur year-round and may be found by sieving vegetation etc from suitable habitats but both adults and larvae spend most of their lives underground, they burrow through damp soil, occasionally surfacing and when they do they leave small mounds of soil around the exit burrows. Little is known of the life-cycle but females lay small batches of eggs in subterranean chambers and both adults and larvae are known to feed on algae (although the form of the adult mandibles would suggest a predatory lifestyle), adults become active on the surface during warm weather and may occasionally occur in small swarms among damp vegetation. Adults are easily found by searching suitable habitats, they occasionally occur by sweeping marginal vegetation or sieving flood-refuse and they are fully-winged and may occasionally be swept above marginal vegetation in the evening.
Adults may be distinguished by the entirely black body, the form of the head and the dorsal microsculpture. 3.2-4.8mm. Head transverse with protruding clypeus and mandibles, vertex transversely and medially impressed in the form of a flattened and inverted Y, eyes small and weakly convex, the inner margin with a strong linear impression that continues towards the base, surface with distinct microsculpture and scattered small punctures. Antennal scape long and broad, segments 2 and 3 elongate, 4-10 quadrate or nearly so and the terminal segment elongate and rounded apically. Pronotum almost semi-circular with protruding anterior angles and a curved apical margin, surface with fine punctures and strong cellular microsculpture, evenly convex and with a median longitudinal impression, lateral and basal margins bordered. Elytra punctured and microsculptured as the pronotum, without striae but impressed along the suture and bordered across the base. Abdomen strongly bordered and with variable cellular microsculpture, each segment with a long erect lateral seta. Femora black or dark brown, tibiae paler brown with numerous fine spines along the external margin and a strong apical spur, tarsi 3-segmented and usually pale yellow. Males may be distinguished by the larger head which has expanded temples and two sharp spines on the anterior margin of the clypeus.