Stenus comma LeConte, 1863

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POLYPHAGA Emery, 1886

STAPHYLINOIDEA Latreille, 1802

STAPHYLINIDAE Latreille, 1802

STENINAE MacLeay, 1825

Stenus Latreille, 1796

Stenus Latreille, 1796

This Holarctic species occurs across temperate areas of the Nearctic and Palaearctic regions, it extends from Portugal to the far east of Russia, China and Japan and extends from lowlands to the alpine zone, it occurs throughout Asia Minor and has recently been recorded from Iran but seems to be absent from North Africa, in Europe it is represented by three subspecies; ssp. aeneiceps Rey, 1884 in the south and east, ssp. peroculatus Puthz, 1986 which is endemic to Italy, and the nominate subspecies which overlaps with the others and is locally common from the Mediterranean north to the UK and higher latitudes of Fennoscandia. In the UK it is locally common throughout England and Wales though absent from much of the West Country and parts of northern England, it is present on Anglesey but absent from Scotland and Ireland. Typical habitats are sandy or gravelly margins of streams and reservoirs with patchy vegetation and plenty of exposed substrate but they may also occur on sparsely vegetated clay or humus and we found them to be common on waterlogged peat cuttings in North Somerset. Adults occur year-round and are active over a long season from February or March until late in the autumn, they are mainly nocturnal, hiding by day in damp soil under debris or among matted vegetation, but they become active on warm days when they may be observed running on the surface, often close to the water and usually in numbers. They fly well, usually in the evening, and are often among the first members of the genus to colonize new sites, and while they may be common on permanently damp areas of floodplains etc, they may also become established on disturbed sites. Both adults and larvae are active surface predators; larvae develop through the spring and summer and adult numbers increase from early summer, suggesting early spring breeding which is typical for many members of the genus. Adults take a range of tiny insect prey but they are primarily springtail hunters, they move rapidly and capture smaller springtails with their extendible labium but larger prey or those covered in defensive scales or setae are attacked and devoured directly without using the labium. Adults are easily sampled by searching among waterside vegetation or under stones and debris; they are easily seen on the surface in hot weather (although not always so easily captured) and will soon appear in pitfall traps though these tend to be unnecessarily destructive. Careful examination will be needed in the field as there are several similar species and colonies tend to comprise more than one.

Stenus comma 1

Stenus comma 1

Stenus comma 2

Stenus comma 2

Stenus comma 3

Stenus comma 3

Aedeagus

Aedeagus

From Tottenham, 1954

5.0-6.0 mm. Entirely black but for the orange elytral macula and pale basal maxillary palpomere, in some specimens the second segment is also narrowly pale at the base but this is variable, entire upper surface with recumbent pale pubescence. Head transverse and wider than the pronotum, with massive convex eyes that occupy the entire margin and a broad and strong central keel, antennae black to dark brown. Pronotum elongate, broadest about the middle and narrowed to a constriction before obtuse anterior and posterior angles, surface strongly and in places confluently punctured, usually with a short longitudinal median impression in the basal half. Elytra quadrate, with rounded shoulders and lateral margins curved to separately rounded apical margins, surface densely and strongly punctured throughout, black with an oval orange spot on the disc. Abdomen tapering to the apex, tergites 1-4 strongly bordered, 5 and 6 less strongly so, basal tergites strongly punctured, especially about the base, apical tergites more finely and sparsely so, all tergites with very fine reticulate microsculpture. Legs long and slender, entirely black or dark grey and finely pubescent, hind tarsi much longer than half the length of the hind tibiae, fourth segment of all tarsi simple. Specimens with the second maxillary palpomere pale about the base can be distinguished by the larger size, the form of the head and the long and narrow aedeagal parameres which have several very long setae at the apex.

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