Coelostoma orbiculare (Fabricius, 1775)

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POLYPHAGA Emery, 1886

HYDROPHILOIDEA Latreille, 1802

HYDROPHILIDAE Latreille, 1802

SPHAERIDIINAE Latreille, 1802

Coelostoma Brullé, 1835

This species is generally common throughout the Palaearctic region from Europe to the far east of Russia and Japan and has recently been recorded from Canada (Ontario); in Europe it is common from lowlands to about 1800 m and extends from the Mediterranean to the UK and far above the Arctic Circle in Fennoscandia, it is present on many of the Mediterranean islands but absent from North Africa. In the UK it is common throughout England and Wales and rather less so across Scotland and Ireland, and with the exception of Orkney and Shetland occurs on all the islands. Typical habitats are well-vegetated margins of stagnant ponds and ditches, they often common among wet reed bed margins and peaty moorland ponds, we have found them under debris in salt marshes in Hampshire and specimens are often present among numbers of other hydrophilids in temporary pools in the spring. Adults usually occur among silty or peaty soil or matted vegetation and moss in shallow marginal situations but they are also common among floating masses of leaves and moss, they are diurnal as well as nocturnal and often come to light in the summer. Breeding occurs in the spring and larvae develop through the summer in marginal situations, they have been sieved from wetland litter samples and presumably inhabit permanently wet litter etc., pupation occurs late in the summer and the resulting adults will go on the overwinter among litter etc. Adults occur year-round; they peak in abundance during late spring and early summer and remain active into the autumn but are rarely found in numbers, they are easily sampled through the season by sweeping among marginal vegetation, and through the winter may be found among litter samples or flood refuse.

Coelestoma orbiculare 1

Coelestoma orbiculare 1

Coelestoma orbiculare 2

Coelestoma orbiculare 2

Coelestoma orbiculare 3

Coelestoma orbiculare 3

4.0-4.9 mm. Broadly oval, convex and continuous in outline, body entirely shiny black or sometimes with the pronotal base narrowly dark reddish, legs dark brown, palps black, antennae pale brown with a black club. Dorsal surface glabrous and finely and densely punctured throughout. Head transverse, broadest across weakly convex eyes that are entire and continuous with the margin, smoothly narrowed to an almost truncate anterior margin, the lateral margin continuous and concealing the antennal insertions and from above, labrum usually hidden from above beneath the clypeus, surface smooth and weakly convex. Maxillary palps shorter than the antennae; the second segment broader than the narrow third and fourth segments. Antennae nine-segmented with an elongate and loose three-segmented club. Pronotum convex and widely transverse, broadest across slightly acute posterior angles and narrowed to obtuse anterior angles, surface evenly convex and lacking depressions or sculpture. Scutellum triangular; about as wide across the base as long, surface densely and very finely punctured and apical margin finely rounded. Elytra broadly-oval and only slightly elongate, with rounded shoulders and a continuous apical margin, without striae but for a sutural striae extending from the apex into the basal half. Legs short and robust, with femora not visible in normal settling, tibiae hardly widened from the base, finely spinose externally and each with two well-developed apical spurs. Tarsi five-segmented and simple; the basal segment of the middle and hind tarsi distinctly longer than the second segment.