Brychius elevatus (Panzer, 1793)
This is a widespread western Palaearctic species distributed from Spain to central Siberia and extending north into Fennoscandia and the UK; in central Europe it is sometimes locally common but in the north tends to be sporadic and generally rare. Here it occurs locally throughout most of Britain and Ireland north to Orkney and including The Isle of Wight, Anglesey, Man and some of the Western Isles but there has been a general decline over recent decades and although still widespread is absent from many of its former sites. The usual habitat is slow running water over gravelly or sandy substrates but they may also be found around sparsely-vegetated lake margins; adults often occur among marginal plants such as brooklime (Veronica beccabunga L.) or in watercress (Nasturtium officinale W.T. Aiton) beds etc, and sometimes in company with other members of the family. Adults occur year-round; they overwinter among aquatic substrate, become active early in the year and remain so until late into the autumn. Breeding occurs in the spring and eggs are laid in aquatic stems or foliage, larvae develop through the spring and summer and pupation occurs out of water among marginal substrate etc, and new-generation adults appear in the autumn. Larvae are known to feed on filamentous algae but adults are omnivores, predating small eggs and larvae and also consuming algae.
3.5-4.4mm. Readily identified as a member of the Haliplidae by the small size, habitus and the form of the hind coxae; these are expanded into plates which are wider than the visible parts of the abdomen. Among the family the present species is easily identified by the broadly-transverse pronotum which is widest in front of almost parallel-sided basal margins. Ground colour yellowish-brown, often with the front and hind pronotal margins darkened and with the elytra darkened at least to some extent and often extensively so. Head smoothly convex and finely punctured, especially around the hind margins of the eyes, antennae 11-segmented and filiform, eyes large and convex. Anterior pronotal angles rounded, posterior angles almost perpendicular and basal margin sinuate laterally and produced medially, surface smooth and finely punctured but for groups of larger punctures towards the base and a long sinuate impression either side of the disc which begins at the base and extends more than half way to the anterior margin. Elytra long and smoothly curved laterally to a slightly obtuse apex, striae relatively strongly punctured and interstices, especially the third interstice, variously raised to form longitudinal ridges for part of their length. Elytral colour varies widely but is generally pale with darker striae or with darker spots around the punctures, and variably and usually indistinctly darker markings before and after the middle. Appendages entirely pale.