Hypocaccus dimidiatus (Illiger, 1807)

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POLYPHAGA Emery, 1886

HYDROPHILOIDEA Latreille, 1802

HISTERIDAE Gyllenhal, 1808

SAPRININAE Blanchard, 1845

Hypocaccus Thomson, C.G,. 1867

This halobiont species is widespread and locally common around the coasts of the Western Palaearctic region, the nominative subspecies is more southern; occurring around the Mediterranean, including many of the islands, across North Africa and the Azores and Canary Islands, while ssp. maritimus (Stephens, J.F., 1830) occurs around the coasts of western and northern Europe, extending north into the south of Fennoscandia and the UK. Here it is widespread around the coasts of England, Wales and southern Scotland; there appears to have been a reduction over recent decades and it has vanished from some of its former sites but it remains locally common in many areas and adults are often very abundant where they are established. Adults are present year-round; they overwinter in soil etc. and become active early in the year, they are generally nocturnal and spend the day buried in sand or under debris and emerge during the evening to forage. Both adults and larvae are predaceous, larvae develop among decaying organic matter, including dung and carrion, where they feed on diptera larvae etc. while adults are more general predators. Typical habitats include beaches and dune slacks, maritime pastures and salt marsh margins and on the continent they are common in wooded areas by the sea, adults are strong fliers, they occasionally come to light and on warm summer nights may be found some distance from the sea. Large aggregations of adults sometimes occur in spring and early summer, hence early in June 2014 we found very large numbers by digging up decaying seaweed just above the upper tide line on beaches in North Somerset, along with numerous other coastal beetles, while extensive searching of the adjacent dune slacks failed to reveal any adults at all.

Adults may be identified by the head structure and distribution of punctures on the dorsal surface; unlike many superficially similar species within the Histerinae the anterior prosternal margin is not produced into a lobe under the head. 3.5-5.0mm. Body glabrous and entirely black, antennae pale with the club and scape substantially darkened, legs black to pale brown. Head transverse with weakly convex eyes, vertex variously impressed medially and frons raised along the inner margin of the eyes, frontoclypeal suture strongly raised; beyond this the clypeus produced forward and truncate or weakly sinuate apically, mandibles long and robust with a broad internal tooth. Pronotum transverse, broadest across the base and narrowed to rounded and produced anterior angles, lateral margins only weakly curved, surface smooth but for a narrow series of punctures along the basal margin. Elytra slightly discontinuous in outline with the pronotum, broadest behind the base and narrowed to truncate apical margins, surface extensively punctured and sometimes completely so but very variable and usually with the basal quarter between the suture sutural and first stria smooth and impunctate, generally more sparsely towards the base and densely beyond the middle; often confluently towards the centre but otherwise discretely, sutural stria complete to apex, 2-4 oblique and incomplete. Pygidium and propygidium punctured throughout. All tibiae broadened to a truncate apex, middle and hind tibiae with several external series of stout spines and a long spur at the inner apical angle, front tibiae with 4-6 strong external teeth and a small terminal spur.

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