Oreodytes septentrionalis (Gyllenhal, 1826)

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ADEPHAGA Clairville, 1806

DYTISCIDAE Leach, 1815

HYDROPORINAE Aubé, 1836

HYDROPORINI Aubé, 1836

Oreodytes Seidlitz, 1887

This is a mostly central and northern European species with a rather erratic distribution; in the south it occurs from Portugal to the Italian Alps, Slovenia and Austria, and to the north it reaches the UK and the Arctic Circle in Scandinavia although it seems to be absent from Belgium, the Netherlands, Denmark and most of the Baltic countries. The species is also widespread across Northern Russia, extending east to Lake Baikal and Mongolia, and there are recent records from Turkey. Records from North America have been found to refer to a different species. In the UK it is local and sometimes common in the West Country and Northern England, Wales and Scotland including Anglesey, Man, Islay and Orkney. Typical habitats are sparsely vegetated and shallow stretches of rivers on shingle or gravel substrates, margins of lakes and reservoirs and often in smaller ponds adjacent to running water, often in upland areas and, at least in Europe most frequently in mountain valleys and foothills. Adults occur year-round; they overwinter out under debris etc. out of water and are active from March until October, peaking in abundance during June and July. Breeding occurs in spring and early summer and larvae develop through the summer, pupation occurs in the summer and winter is passed in the adult stage. Adults have been observed to fly but flight muscle development varies and so it is likely that not all specimens can do so. Sampling adults is easiest by sweeping suitable marginal habitats and while the species is generally local and uncommon they tend to occur in numbers.

3.0-3.6 mm. Broadly elongate-oval, distinctly constricted between the pronotum and elytra and often with the elytral apex slightly produced. Dorsal surface glabrous, colour variable but typically entirely yellow or yellowish-brown, often with the forebody a little darker, head with two interocular pot and the basal margin black, pronotum with four pot on the disc, the posterior pair larger, and often a smaller dark mark toward the lateral margin, elytra with the suture and seven longitudinal lines black; only the third reaching the base and the outermost usually abbreviated and interrupted about the middle. Ventral surface extensively black with the epipleura lightly paler and the hypomeron pale. Antennae pale with four to six apical segments variously darkened, palps extensively dark, legs pale or with the tibiae and tarsi darkened apically. Head proportionally large, finely punctured and smooth or with weak oblique impressions between large convex eyes that protrude only slightly from the outline, and evenly rounded anteriorly (from above.) Pronotum widely transverse, broadest in front of rounded posterior angles and narrowed to slightly protruding anterior angles, basal margin produced medially, surface finely punctured throughout with larger punctures behind the basal and apical margins and a curved longitudinal impression towards each lateral margin. Metatrocanters sparsely pubescent and with only a few fine punctures.  Elytra finely punctured and microsculptured throughout and scattered larger punctures between the striae. Basal front and middle tarsomeres dilated, only slightly more so in males, hind tarsi normal.

Oreodytes septentrionalis

Oreodytes septentrionalis

© Lech Borowiec