Limnebius aluta Bedel, 1881
This is a mostly lowland species of central and northern Europe although it has recently been recorded from Ukraine; it is locally common from France to Italy, Romania, Slovakia and Poland and north to the Baltic countries where it is sometimes common in southern Sweden and Norway. In Northern Europe it occurs among moss and algae on the margins of densely vegetated stagnant pools and ponds, silt lakes and inflows, mostly in open situations but further north commonly in open deciduous woodland. Specimens taken from wet meadows and peat ditches in north east Poland in 1974 were found to be infected with the novel fungus Hydrophilomyces limnebii Sarna & Milewska, 1977. In the UK it is very local and scarce; there are widely scattered records across Wales and England as far north as Yorkshire, they are mostly isolated but there are clusters of records across East Anglia which seems to be the UK stronghold for the beetle. Adults occur year-round and are active over a long season from February until late in the autumn, peaking from April until June and again in late summer and autumn, they typically occur among moss and litter on wet mud or silt among marginal vegetation and, despite being very local, adults may occur in large numbers; along silty fen margins in east Anglia they sometimes swarm in hundreds. Little is known of the life-cycle but typical of the family adults are probably feed on microscopic animals and plants among aquatic substrates and are spring breeders while larvae develop through the spring and summer in wet marginal situations.
This is the smallest of our UK species, between 1.1 and 1.3 mm, and may be distinguished further by the very finely and often indistinctly punctured head and pronotum. Body long-oval, broadest towards the base of the pronotum and almost continuous in outline, black to dark brown with the margins paler brown, legs brown or reddish-brown, antennae and palps yellow with darkened apices. Head transverse, broadest across the base and smoothly rounded anteriorly, eyes continuous with the lateral margin, labrum emarginate, palps about twice as long as the antennae which are 9-segmented with a 5-segmented pubescent club. Pronotum broadest in the basal half and smoothly curved to almost straight apical and basal margins, surface smoothly convex and with fine reticulate microsculpture. Elytra broadest behind the shoulders and evenly narrowed to near-truncate apical margins, without striae or distinct punctures, microsculpture fine but distinct, in places polyhedral but across the disc sometimes elongate and transverse. The sexes are very similar but males have the basal segments of the front tarsi more widely dilated compared to those of the female, this is subtle and comparative but, as in all members of the genus, the male has six visible abdominal sternites while the female has seven.