Pomatinus substriatus (Müller, P.W.J., 1806)

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POLYPHAGA Emery, 1886

BYRRHOIDEA Latreille, 1804

DRYOPIDAE Billberg, 1820 (1817)

Pomatinus Sturm, 1853

This Western Palaearctic species occurs mostly across southern and central Europe from Portugal to Greece; it extends south into Algeria and Morocco and is known from Lebanon, Syria, Israel and Turkey. The eastern extent of the distribution seems to be Ukraine although it probably also occurs in parts of European Russia and it has been reported from Turkestan, and to the north it reaches the UK, Lithuania and southern Sweden. The species occurs from lowlands to about 2000 m in Europe; it is locally common across much of the south but generally local and rare in the north. In the UK it is widespread though local across Wales and the West Country but otherwise very scarce with records scattered across England north to the Scottish border. Typical UK habitats are lowland streams and rivers, often in shaded areas, where the adults occur among substrate, under stones or on submerged timber or tree roots. On the continent (Serbia) the species predominantly inhabits stretches of rivers with medium and large stones among the substrate. Unlike Dryops, which are mostly riparian, Pomatinus adults are aquatic and use a plastron for breathing, they have been recorded in all months from March until November, they peak in abundance during September and again in April and teneral adults have been found during August and September. Mating seems not to have been observed but females are known to oviposit into submerged decaying logs during the spring. Larvae develop among riparian substrate, often where it is periodically flooded; they feed on damp decaying wood or on plant remains in the soil. Larval development proceeds through the summer and pupation occurs in a subterranean cell near the waterline. The Larva resembles a heavily-sclerotized wireworm; it has a single medial hook on the eighth tergite and paired hook-like urogomphi and deep grooves on the ninth tergite; larvae of Dryops lack these hooks and grooves. Adults can be extracted from aquatic substrate or debris, they often occur in numbers below submerged stones etc. and they sometimes leave the water on warm days. They have been swept in flight and come to light on warm spring and summer evenings.

Pomatinus substriatus 1l

Pomatinus substriatus 1l

© Lech Borowiec

Pomatinus substriatus 2

Pomatinus substriatus 2

© U.Schmidt

4.2-5.5 mm. Elongate and discontinuous in outline, body dark grey to black, finely punctured and with fine recumbent yellowish pubescence throughout, legs pale with darker femora. Head smoothly convex between large, weakly convex eyes which have tiny scales between the facets. Antennae short and highly modified, as in Dryops, pale orange or yellow but for the dark second segment which is expanded and angled internally. Pronotum transverse, broadest behind the middle, narrowed to projecting anterior angles and sinuate before slightly acute posterior angles, apical margin straight, basal margin straight in front of the scutellum and strongly arched laterally, surface smoothly convex and lacking the lateral furrows seen in Dryops. Elytra slightly dilated from sloping shoulders to a weakly acuminate apical margin, without striae but usually with several weak longitudinal impressions. Legs long and slender with all femora of similar width and tibiae only slightly broadened from the base. Tarsi with five simple segments; the basal segments mostly elongate and the terminal segment very long and gradually broadened to the apex. Claws smooth and without a basal tooth.