Oreodytes alpinus (Paykull, 1798)

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ADEPHAGA Clairville, 1806

DYTISCIDAE Leach, 1815

HYDROPORINAE Aubé, 1836

HYDROPORINI Aubé, 1836

Oreodytes Seidlitz, 1887

This species is widely distributed across northern parts of the Palaearctic region from Scotland to the far east of Russia. In Europe it is generally very local and rare; it is absent from Denmark and the southern Baltic countries but generally distributed across Fennoscandia from the south of Norway to above the Arctic Circle with the exception of southern Sweden and, so far as is known, much of Finland. The species was first recorded in the UK in 1985, and is now known from several larger lochs in Caithness and East Sutherland. The typical habitat is poorly-vegetated oligotrophic lakes on exposed sand or gravel substrates and in Norway is has also been recorded from shallow brackish lakes. in the UK it occurs in areas of lochs where the substrate is predominantly sandy and unstable due to energetic wave action. Adults are active from May until September, peaking in abundance during August although they overwinter and so might be found at any time. Breeding is thought to occur in the spring and larvae develop during the spring and summer to produce new-generation adults from mid-summer.

4.2-5.0 mm. Elongate and discontinuous in outline with the pronotal base distinctly narrower than the elytra across the shoulders, glabrous and finely reticulate. Appendages pale brown, often with the distal antennomeres darkened apically. Head yellow with the base and an angled transverse mark between the eyes black. Pronotum transverse, broadest towards the base and unevenly curved laterally; almost straight towards the base but rounded towards protruding anterior angles, surface evenly convex with a fine longitudinal impression towards each lateral margin. Pronotal colour varies but usually substantially pale brown with a darker marking across the centre of the basal margin and (sometimes) two dark maculae in the basal half. Elytra pale brown to yellow with the suture narrowly darkened and six dark longitudinal lines which do not extend to the basal margin and are often variously united at the apex, and two variable sub-lateral dark spots. The darker elytral markings are variable in width and sometimes confluent, especially the inner two lines about the middle and the sub-lateral spots. Elytra with distinct punctures between the longitudinal series. Epipleura visible to the base in lateral view, without a transverse ridge towards the base.  Ventral surface black or dark brown with the hypomera and epipleura yellow. Legs yellow or with the basal segments of the front and middle  tarsi, and the middle tibiae darkened. Basal segments of the front and middle tarsi dilated and front claws elongated in males. Lateral elytral margin produced into an obtuse tooth towards the apex in females.

Oreodytes alpinus 1

Oreodytes alpinus 1

© Marko Mutanen, University of Oulu

Oreodytes alpinus 2

Oreodytes alpinus 2

© Marko Mutanen, University of Oulu