Euaesthetus ruficapillus (Laccordaire, 1835)

This species is locally common across western and northern Europe from France through northern Italy to parts of the Balkan Peninsula and north into the UK and reaching the most northern parts of Scandinavia, to the east it extends through the Caucasus and Russia into Siberia. In the UK it occurs sporadically throughout England, Wales, southwest Scotland and Northern Ireland; it is locally common throughout Wales, including Anglesey, East Anglia and the midlands but much more local elsewhere. Typical habitats are organic-rich wetland margins, fens, marshes and reed beds etc. while in Europe they also occur during the warmer months in ephemeral habitats such as small flood-plain ponds and even puddles in a diverse range of situations.  Adults occur year-round; they overwinter in tussocks or waterside litter and are active from March until October, peaking in abundance from May until July. Little is known of the biology but adults are predatory and the larvae are thought to be as well, and from the phenology it is likely that breeding occurs in the spring and that larvae develop through spring and early summer. Adults are tiny and inconspicuous and so are probably under-recorded. Probably the best way to find them is by taking samples for extraction, they generally occur under decaying and matted vegetation or among clumps of sedges or moss, sometimes where these are partially submerged. They usually occur in numbers, occasionally swarm in early summer, and are fully-winged and so may suddenly occur at well-worked sites.

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1.5-1.8 mm. Although small and suggestive of various Omaliinae or Oxytelinae, this species is easily recognized by the form and structure of the head. Elongate with a relatively large head, cordate pronotum and gently tapering abdomen, body entirely reddish-brown or with the pronotum and/or elytra darker, sometimes black, appendages reddish-brown, often paler than the body, and often with the antennal club darker. Head with widely rounded in front of convex and protruding eyes, temples long and weakly curved but usually hidden within the thorax, surface smooth and shiny across the base, otherwise strongly and densely punctured throughout, the punctures often touching but not confluent. Anterior margin of the labrum with a series of long and slender spines, mandibles long and slender; the inner margin crenulate before a sharp median tooth. Maxillary palps about half the antennal length, the penultimate segment (which appears as the last segment due to the diminutive terminal segment) narrow at the base and expanded towards the apex. Antennae inserted dorsally, inside the base of the mandibles and well in front of the eyes, 11-segmented with a 2.segmented club. Pronotum slightly transverse, broadest in front of the middle and narrowed to perpendicular posterior angles, surface densely punctured across the disc and with a longitudinal arcuate impression either side towards the base, basal margin with three longitudinal keels that reach, or almost reach, the impressions. Elytra transverse and slightly dilated from rounded shoulders to curved apical margins, sutural margin raised but otherwise without striae, surface randomly punctured, less strongly than those on the pronotum, the cuticle between these flat and shiny, without granular microsculpture. Abdomen almost parallel in the basal half, with narrow but obvious lateral margins, all segments finely punctured and pubescent, apical sternite deeply excised in males, much less so in females. Legs long and slender, femora unarmed and tibiae without lateral setae or obvious terminal spurs. Tarsi 4-segmented, the basal segments weakly lobed.