Ischnosoma Stephens, 1829
A large and almost cosmopolitan genus of more than 100 species, it is diverse and widespread in the Palaearctic, Oriental and Australasian regions but much less so in the New World where 13 species are known from North America and a further five occur in Central America. The European fauna includes eleven species; the greatest diversity is in northern Mediterranean regions and the majority are either endemic to certain countries or have limited distributions as follows. I. loebli Kocian, 1997 occurs in the Near East but also on Cyprus, I. bergrothi (Hellen, 1925) occurs across the Northern Palaearctic region and is widespread in the Baltic countries while I. plagiatum (Fairmaire, 1860) is widespread in south Western Europe and extends to North Africa. Of the endemics, I. winkleri (Bernhauer, 1915) occurs in Ukraine, I. spelaeum (Scriba, 1870) in Spain, I. corsicum Kocian, 1997 on Corsica, I. kociani Schulke, 1998 in Greece, I. ludwigi (Reitter, 109) in Croatia and Bosnia and Herzegovina, and I. monilicorne (Wollaston, 1864) on the Canary Islands. Our two UK species, I, longicorne (Maklin, 1847) and I. splendidum (Gravenhorst, 1806) are Holarctic in distribution. The species usually occur among moss or fungi, under bark or in decaying wood or among rotting vegetation in a variety of damp habitats but often in open deciduous woodland and damp grassland. Adults generally occur throughout the year and breeding occurs in the summer, both adults and larvae occur in moist situations, they are fast-moving nocturnal predators of other insects etc., although some species are also mycophagous and some are more specifically associated with damp mosses. Some are more specialized e.g. I suteri Campbell, 1991 is endemic to high altitudes in the Appalachians, while some e.g. I. splendidum, occur more generally from lowlands to middle mountain altitudes.
The species are medium sized, 3.5-6.0 mm. elongate and slender, forebody glabrous but for various erect sensory setae, elytra with setiferous punctures and often characteristic impressions, abdomen with numerous sensory setae as well as much finer pubescence, legs are long and slender. Colour varies from pale to very dark brown; some species are strikingly bicoloured with the head, pronotum, elytra or various abdominal tergites strongly contrasting (when mature). Head with temples narrowed and variously produced in front of the eyes and a setiferous puncture near the posterior margin of each eye. Eyes large and following the outline, temples smoothly curved. Antennae inserted outside the outer margin of the mandibles and near the anterior margin of the eyes, distinctly longer than the head and pronotum combined, segments nine and ten quadrate to slightly elongate. Terminal maxillary palpomere diminutive and only about half as wide as the previous segment. Pronotum transverse, broadest near the base and narrowed to a rounded apical margin, posterior angles rounded, basal margin sinuate, surface smooth, with or without microsculpture but without impressions or structure. Elytra longer than the pronotum, at most only slightly dilated from rounded shoulders to recurved apical margins, sutural border raised, surface with rows of setiferous punctures along the sutural and lateral margins and below the shoulders. Abdomen long and gradually tapering from the base, basal segments strongly bordered, tergites smoothly convex (not impressed across the base) and finely punctured and pubescent throughout, in males often with conspicuous patches of setae on the fifth and/or sixth ventrites. Basal segment of middle and hind tarsi with only fine pubescence ventrally, without longer setae, terminal segment of hind tarsi not longer than the previous segment. Formerly included within the genus Mycetoporus Mannerheim, 1830, but here the antennae are at most only slightly longer than the head and pronotum combined, the penultimate antennomere is usually transverse and the last segment of the hind tarsi is longer than the penultimate segment.
Our UK species may be distinguished as follows:
-Larger, 4.5-5.5 mm. Head reddish brown, concolorous with the pronotum, broader and less produced anteriorly and smooth, without microsculpture. Subhumeral series consisting of 7-10 punctures. In males apical margin of sternites five and six with short setae medially and longer setae laterally.
-Smaller 3.5-5.0 mm. Head usually much darker than the pronotum, narrower and more produced anteriorly and with fine transverse microsculpture. Subhumeral series consisting of 5-7 punctures. In males the apical margin of the fifth sternite with a few longer setae at near the lateral margin, sixth sternite with a median patch of setae and two tufts of setae towards the apex.
Ischnosoma longicorne (Mäklin, 1947)
I. longicorne is locally common throughout Europe to the far north of Fennoscandia, to the south it occurs on many of the Mediterranean islands and is recorded from Morocco and Algeria. In the UK it is widespread but local and generally scarce across Central and Southern England and Wales and there are older records further north to the Scottish border, suggesting a recent decline. Adults are present year-round, they overwinter among tussocks or in moss etc and are active from March until November, peaking in abundance during June. They may be found under debris or in moss or decaying fungi in most open and damp situations; they usually occur as single specimens or in pairs but numbers may appear at large decaying terrestrial fungi in the autumn.
Ischnosoma splendidum (Gravenhorst, 1806)
I. splendidum is generally common from lowlands to middle mountain altitudes throughout Europe to the far north of Fennoscandia and is by far the most frequently recorded member of the genus. In the UK it is common across England and Wales north to South Yorkshire, although rare in the West Country, and sporadic and rare further north to the Scottish Highlands and the Outer Hebrides. Adults are present year round; they are often active during the winter and they peak in abundance earlier than the previous species, usually during April or May. They occur in most damp habitats, especially open woodland where they often appear under bark or logs, also under matted vegetation on arable borders, moorland, peat bogs and among marginal vegetation including reed beds. Although mostly nocturnal they will soon be encountered by general searching under logs etc, they sometimes appear among flood refuse and may occur in suitable extraction samples at any time.