Hydroporus pubescens (Gyllenhal, 1808)
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ADEPHAGA Clairville, 1806
HYDROPORINI Aubé, 1836
Widespread and locally common from lowland to sub-alpine altitudes throughout most of Europe from the Mediterranean north to the UK and central Fennoscandia, this species extends across North Africa into Asia Minor, western Russia and Iran and is known from the Canaries, Channel Islands and Faroe. It is generally common throughout the UK including all the islands north to Shetland, occurring to mountain altitudes in the west and north but becoming more local in drier parts of south and central England and in the south of Ireland. Adults occur year-round; they are active over a long season from early spring, peaking in abundance during May and June and may be found during mild winter spells. Typical habitats are small or temporary water bodies, they often occur in small ponds with little or no vegetation and cattle troughs but may also be common among dense marginal vegetation on most substrates including peat and chalk, they are often common in brackish water pools but only rarely in running water or larger water bodies. The species is univoltine; breeding occurs in the spring and eggs are laid among aquatic vegetation, the predaceous larvae develop through the spring and early summer, passing through three instars and leaving the water when fully grown to pupate among marginal substrate. New generation adults occur from early summer, they enter the water to feed and then may disperse by flight or remain until the autumn, where the habitat dries out during the summer they often remain under debris or in damp soil and become active again when the water returns. Adults tend to be abundant but they often occur among numbers of other common and sometimes superficially similar species and so samples should be taken for careful scrutiny.
3.2-3.8 mm. Elongate-oval, continuous and rather broad in outline, pronotum and elytra with dense pale pubescence (which may become extensively rubbed in life), typically with the elytra pale and contrasting with the dark pronotum, extensively dark specimens occur but here the elytra are usually a little lighter and the pronotal margins are usually narrowly pale, head usually dark with the anterior and basal margins pale although this latter may be hidden within the thorax, legs reddish brown, antennae extensively dark but variably pale at the base. Although variable in colour the surface structure is distinctive; the basal half of the pronotum and elytra are extensively smooth and shiny, this varies a little but the contrast with the microsculptured anterior part of the pronotum is obvious, and the apical abdominal sternite is shiny and lacks microsculpture in both sexes (although it is punctured and pubescent as the preceding sternites), this last feature will distinguish pubescens from all other UK members of the genus. Ventral surface moderately convex, coarsely, though in places rather sparsely, punctured and almost entirely black, the prosternal process narrow, convex and transversely grooved across the base. The tarsi are 5-segmented but the front and middle tarsi appear to be four segmented as the tiny fourth segment is largely concealed within the lobes of the third. Sexual dimorphism is not obvious in this species; males have the basal segments of the front tarsi only narrowly dilated and the claws are not modified.