Stenus guttula Müller, P.W.J., 1821

This species is widespread across the western and central Palaearctic regions, extending from Europe and Asia Minor into eastern Siberia; it is generally common across Southern Europe and North Africa, including the Mediterranean and Atlantic islands, but less so moving north where it becomes much more local, reaching as far as the UK, Denmark and the Baltic countries although only in southern parts of Fennoscandia. In the UK it is locally common throughout England and Wales, including all the islands, much more local and scarce in the Scottish Highlands and rare and scarce and mostly coastal in Northern Ireland.  The usual habitat is wetland margins, lake shores, banks of slow-moving streams and rivers, seepages and coastal estuaries and dune pools, usually on clay or fine sandy or gravelly substrates and usually with patchy vegetation and areas of moss and layers of decayed vegetation. Adults are diurnal and predatory, hunting on the surface during warm weather but otherwise remaining concealed under debris or in moss or soil etc, they do not climb vegetation but are capable of moving rapidly on the water surface when necessary. Little is known of the biology but, typical of the group, reproduction probably occurs in spring and early summer and the larvae predate other small invertebrates on or within the soil. Adults are present year-round; the overwintering sites are not known but are unlikely to be far from water, they are rarely recorded during the winter but are active over a long season from March until October, they are most common in the spring and peak in abundance during June. They may be sampled by searching under debris or matted vegetation or by catching then as they run during sunny spells, flooding areas of likely substrate can often make them active and pitfall-trapping may produce numbers of adults, usually along with plenty of other marginal carabids and staphs and so traps will need to be examined frequently.