Stenus juno (Paykull, 1789)

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POLYPHAGA Emery, 1886

STAPHYLINOIDEA Latreille, 1802

STAPHYLINIDAE Latreille, 1802

STENINAE MacLeay, 1825

Stenus Latreille, 1796

Stenus Latreille, 1796

This is among the most widespread and generally common members of the genus; it occurs throughout the Palaearctic region from Europe and North Africa through Asia Minor and Russia to China and Japan and is widespread and common across Canada and the United States. The distribution includes all of Europe from the Mediterranean, including most of the islands, to the far north of Scandinavia; it is generally common from lowlands to low mountain altitudes but, despite its occurrence so far north, it is generally absent from higher altitudes. In the UK it is abundant throughout England, Wales and the north of Ireland and rather more local and with a more eastern distribution further north to Orkney, in Southern Ireland it is very local and scarce and tends to be more coastal. Typical habitats are wetland margins and permanently damp floodplain grassland although in Northern Europe it is often common among leaf-litter etc. in damp woodland. Adults are present year-round; they are generally active from March until October but may often be observed during mild winter spells, peaking in abundance during May and June. They are diurnal predators and more or less strictly terrestrial, climbing vegetation only when the substrate becomes flooded, they move rapidly and generally hunt in the open on bare areas of damp soil among patchy vegetation. Large populations may be found near all kinds of water margins although they are much less common on peat; they are quick to colonize new sites and may be common on disturbed stretches of river banks etc. Their habitats are always rich in decaying organic matter and bacteria along with abundant springtails and other small arthropods, and while they may be common on sandy or chalky soils they are probably more so on heavier clay or silty substrates. They hunt in typical Stenus fashion by capturing prey with adhesive secretions exuded onto pubescent pads at the end of a modified and extrusible labium. Little is known of the biology but from the phenology it is likely that breeding occurs in late spring and early summer and that larvae develop through the summer. With practice the species may be recognized in the field but other Stenus (along with numerous carabids etc.) often occur among populations of juno and there are a few closely similar species so specimens will need to be taken for critical examination.

Stenus juno 1

Stenus juno 1

Stenus juno 2

Stenus juno 2

Aedeagus

Aedeagus

From Tottenham, 1954

5-6mm. A large and shiny black species with sparse and rather inconspicuous dorsal pubescence. Head slightly narrower than the elytra, with massive eyes that occupy the entire lateral margins. Surface densely punctured throughout and distinctly raised medially between well-defined furrows. Frons and clypeus with longer and denser pale pubescence. Mandibles orange or red, slender, curved and split at the apex. Basal maxillary palpomeres pale, terminal segment darkened, antennae entirely dark. When fully extended the feeding apparatus is much longer than the head and pronotum combined. Pronotum slightly longer than wide, broadest about the middle, evenly curved to a rounded apical margin and slightly sinuate before obtuse posterior angles, surface densely punctured throughout and without a distinct central furrow. Elytra (measured along the suture) clearly longer than the pronotum, weakly dilated from rounded shoulders to incurved apical margins, surface uneven and densely punctured. The posterior elytral margin lacks the conspicuous fringe of pubescence seen in the superficially similar S. calcaratus Scriba, 1864. Basal abdominal tergites with strongly raised lateral borders and a small but conspicuous median ridge in the basal half, punctures finer than those on the elytra and usually sparser towards the apices. Legs long and slender with tarsi about as long as the tibiae and without bilobed segments. Males may be distinguished by the thickened and pubescent hind femora. Aedeagus very distinctive.