Stenus juno (Paykull, 1789)

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.