Tetartopeus terminatus (Gravenhorst, 1802)
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POLYPHAGA Emery, 1886
STAPHYLINOIDEA Latreille, 1802
PAEDERINI Fleming, 1821
Tetartopeus Czwalina, 1888
This transpalaearctic species is locally common throughout Europe from northern Spain to central Italy and into the northern Balkans to the south and north to the UK and above the Arctic Circle in Fennoscandia; it is more common in central and northern regions, less so in the south and seems to be absent from most of the Mediterranean islands. In the UK it is generally common across England and Wales, including the islands, and there are scattered records from Scotland, in Ireland it is common across the north but much less so in the south. Typical habitats are wetland margins, peat bogs and Carr, often on clay soils or gravel, and also, especially in northern Europe, in permanently damp grassland, and deciduous and mixed woodland. Adults are present year-round; they overwinter among sedges or moss etc. and are active over a long season from March until October or November, often emerging during mild winter spells, and peaking in abundance during May and June or, in central Europe, during April and May. Very little is known of the life cycle but both adults and larvae are predatory, mating has been observed in June and it is likely that only adults overwinter. Adults are nocturnal, spending the day under matted algae or among decaying vegetation although they may venture into the open on the warmest of summer days, by night they roam among waterside vegetation and may venture out onto bare ground or pathways. They are probably wing-dimorphic but fully-winged specimens are common and sometimes appear in flight interception traps. Adults usually occur in single numbers or pairs and are easily sampled by sieving or searching through waterside debris or extraction samples, they may also appear in numbers among winter flood refuse.
5.5-8.0 mm. Elongate and rather parallel-sided with the forebody and abdomen narrower than the elytra, body finely pubescent and entirely shiny black or with the head black and otherwise dark brown, often with a pale mark at the posterior elytral angles, antennae and palps dark to pale reddish-brown, legs pale brown or with the femora darker. Head with weakly convex eyes and long, rounded temples, surface moderately strongly but not densely punctured, the disc smooth but towards the base with cellular microsculpture. Penultimate maxillary palpomere long and expanded from the base, terminal segment diminutive, mandibles curved and with a strong internal tooth. Antennae inserted laterally near the front margin of the clypeus, filiform and very long, reaching back into the basal third of the elytra, with all segments elongate. Neck short and narrow, about one-third the width of the head. Pronotum elongate and quadrangular, the basal margin curved and finely bordered and the apical margin produced forward, surface without sculpture, punctured about the same as the head and with extremely fine granular microsculpture. Elytra slightly dilated or almost parallel-sided from rounded shoulders to rather strongly incurved apical margins, without striae but usually with a well-defined sutural impression, at least towards the apex, surface strongly punctured and in placed roughly sculptured, especially towards the apical angles, the cuticle mostly smooth and shiny. Abdomen finely punctured except across the base of the tergites. In males the eighth sternite has a small triangular excision, in females it is rounded. Females can often be identified by the form of the abdominal apex; the ninth tergite is long, narrow and divided to the base and the tenth is triangular and finely rounded apically. Legs long and robust, the front femora with a strong ventral tooth and the middle and hind femora simple. Tibiae slender, front tibiae narrowed and densely pubescent internally from the base and broadened from about the middle, middle and hind tibiae only weakly broadened from the base and all with a very fine apical spur. Tarsi 5-segmented; basal segments of the front tarsi dilated in both sexes.
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The yellow marks at the outer elytral angles are a good guide to the species but specimens with all black elytra will need to be examined closely, the aedeagus is subtly distinctive; in lateral view pointed and strongly curved apically, almost hooked, with the ventral margin of the curved part almost perpendicular to the base of the median process.
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Superficially similar to various Staphylininae but with diminutive terminal maxillary palpomeres and the antennae inserted outside the base of the mandibles.