Stomis pumicatus (Panzer, 1796)
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ADEPHAGA Clairville, 1806
PTEROSTICHINI Bonelli, 1810
Stomis Clairville, 1806
This is a locally common species, sometimes recorded frequently but rarely in numbers, occurring from Portugal eastwards to Slovakia although it seems to be absent from much of northern Europe, and to the east of the range it is represented by subspecies obenbergeri Kult, 1940. It was first recorded in North America in 1984 from European introductions and is now established in eastern Canada. Here it is widespread though generally scarce throughout the UK north to Inverness; it seems to be frequent only in the south and east and records in the west tend to be more coastal, it is present on Man but apparently absent from our other islands. Adults occur year round in a range of mostly damp and shaded habitats including woodland, parkland, moorland and occasionally in domestic gardens, they are active over a long season from early spring, peaking in abundance during May and June, until late in the autumn and overwinter among moss, leaf litter or under bark, sometimes occurring in flood refuse samples. They are often associated with humus-rich soil in disturbed habitats and, at least on the continent, are usually among the first carabids to occur in newly established woodland. During the spring and summer they are active nocturnally; we have found them by torchlight on parkland pathways at several Watford locations and among heather roots and waterside vegetation at Bricket Wood Common, during the day they rest beneath logs or stones or among grass tussocks, and they may also be at least partly subterranean as specimens have been found in the runs of small ground-nesting mammals. The species is flightless and breeds in the spring.
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The small size, elongate form and dark colouration is suggestive of Patrobus or a small Pterostichus in the field but the unique form of the mandibles will make Stomis immediately obvious under a hand lens.
6.5-8.5mm. Overall dark brown with pale appendages. Elongate and narrow, generally rather parallel. The mandibles protrude forward and are as long as the head; the right mandible being wider and a little shorter than the left. The first antennal segment is as long as the following two combined. Head impunctate and finely microsculptured, with two setiferous punctured beside each eye and two short furrows on the lateral clypeal margins. Pronotum cordate, strongly narrowed to perpendicular posterior angles and with a single linear furrow either side of the base, surface impunctate and finely microsculptured. The anterior margin of scutellum lies in front of the basal border of the elytra. Each elytron with eight deep and moderately-strongly punctured striae but without a scutellary stria, the interstices weakly convex, impunctate and very finely microsculptured. Wings absent or very short. Male with basal protarsal segments dilated.
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STOMIS Clairville, 1806
This is a Holarctic genus of around 40 species included in 2 subgenera. The only species included in the subgenus Neostomis Bousquet, 1983 is S. termitiformis (Vandyke, 1925), which is also the only species to occur naturally in North America and Canada. All other species are included in the subgenus Stomis s.str. Many occur only in the eastern Palaearctic, including China and Japan, and several western species have a limited distribution e.g. S. benoiti Jeannel, 1953 from France, S. bucciarellii Pesarini, 1979 from Italy, S. danielanus Semenov, 1904 from Georgia and S. tschitscherini Semenov, 1904 from Azerbaijan. The only species to occur in the U.K. is the widespread Eurasian S. pumicatus (Panzer, 1795), and of the 6 European members of the genus the only other widespread species is S. rostratus (Duftschmid, 1812). The genus is characterized by the structure of the antennae combined with the asymmetrical and elongate mandibles.