Orectochilus villosus (Müller, O.F., 1776)

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ADEPHAGA Clairville, 1806

GYRINIDAE Latreille, 1810

GYRININAE Latreille, 1810

ORECTOCHILINI Régimbart, 1882

Orectochilus Dejean, 1833

This widespread species occurs throughout Europe, except for the far north, and extends south into northern Africa and east through the Caucasus and Asia Minor to Siberia, China and Korea; over this range it is present as several subspecies, at least two of which occur in Europe; the nominate subspecies occurs throughout the entire range while ssp. bellieri Reiche, 1861 occurs in North Africa, Corsica and Sardinia. It is locally common throughout the UK to the far north of Scotland including various Western Isles, Anglesey and Man but not, apparently, on the Isle of Weight or Scilly. Adults occur year-round; they are active from May until October and peak in abundance during April and again in mid-summer. Typical habitats are rivers, streams and wave-swept margins of large water bodies, generally where there is marginal or overhanging vegetation where the nocturnal adults hide during the day, and they occasionally occur in brackish water in coastal situations. Adults are easy to observe as they gyrate on the water surface at night, often close to overhanging banks or beside fast running or falling water, they may occur in numbers and are sometimes locally abundant but they are generally less gregarious than other whirligigs, they need to be searched for very thoroughly and so are probably under-recorded, they may also appear in the water net when sweeping marginal situations by day. Reproduction occurs in the summer and eggs are laid on the roots of aquatic plants, larvae develop among sand and gravel in shallow water and are thought to overwinter and pupate in the spring. Both adults and larvae are predaceous and have been observed feeding on diptera larvae.

5.5-6.5mm.  Elongate and very convex so that the lateral margins of the pronotum and elytra are reflexed and not visible from above. Body entirely dark brown, appendages pale brown or reddish-brown. Entire upper surface with very fine puncturation and recumbent yellow pubescence. Head transverse with front margin of clypeus curved inwards and finely bordered. Upper eyes entirely visible from above, lower pair hidden under expanded side margin. Antennal cavities wide and deep in front of eyes, surface very finely microsculptured, the pubescence pointing forward, that behind the eyes pointing down. Pronotum very transverse and highly arched, the anterior margin sinuate and curved backwards behind the eyes, the hind margin sinuate and depressed in front of the scutellum. Surface finely microsculptured, the pubescence pointing obliquely backwards. Scutellum glabrous. Elytra widest before middle and only weakly truncate at apex, pubescence pointing backwards, colour generally lighter towards apex. Lateral margins of pronotum and elytra continuous; reflexed and evanescent towards the elytral apex. Margins and underside pale brown. Front legs long and raptorial; inner margin of tibiae with very fine forwardly pointing spines, outer margin sinuate and weakly produced into a sharp angle at apex. Front tarsal segments broad and each with a spine on the inner side at the apex. Claws long and smooth. Middle and hind legs broadly dilated. Claws small and strongly curved at base.

In the U.K. this is the only pubescent whirligig and so the identification should be certain.

Orectochilus villosus 1

Orectochilus villosus 1

Orectochilus villosus 2

Orectochilus villosus 2

© Lech Borowiec http://www.cassidae.uni.wroc.pl/Colpolon/index.htm

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