SCYDMAENINAE Leach, 1815
Ant-like Stone Beetles
Includes rare and infrequently recorded species, most occur among decaying vegetation or in soil.
Formerly considered as a distinct family but incorporated into the Staphylinidae in 2009 by Grebennikov, V.V. & Newton A.F.; it is a large and cosmopolitan group of about 5000 species in 90 genera. The subfamily is divided into 11 tribes which are grouped into 2 supertribes, each of which were formerly classified as subfamilies of the Scydmaenidae. The largest is SCYDMAENITAE Leach, 1815 which includes 8 tribes and is cosmopolitan with by far the greatest diversity in tropical regions. Eutheiini Casey, 1897 includes 5 genera and is most diverse in northern temperate regions. Cephenniini Reitter, 1882 includes about 200 species in 11 genera and is cosmopolitan, the greatest diversity is in the Oriental region. Glandulariini Schaufuss, 1889 (=Cyrtoscydmini Schaufass, 1889) is by far the largest group within the subfamily with more than 3700 species included in about 50 genera, most of which occur in tropical and subtropical regions. Plaumanniolini Costa Lima, 1962 includes only a few species of the single Neotropical genus Plaumanniola Costa Lima, 1962. Siamitini Franz, 1989 includes a single monotypic genus from Thailand, formerly included within the Glandulariini. Chevrolatiini Reitter, 1882 includes about 12 species of the single genus Chevrolatia Jacquelin du Val, 1850, 3 occur in Europe and 3 are Nearctic, they otherwise occur Central America and the Afrotropical region. Leptoscydmini Casey, 1897 is a Nearctic group including only the single genus Leptoscydmus Casey, 1897. Scydmaenini Leach, 1815 includes 7 genera and is cosmopolitan. MASTIGITAE Fleming, 1821 includes about 130 species in 9 genera and (variously) 4 tribes. The group is morphologically very diverse and some have greatly enlarged or modified antennae or palps and in some the male genitalia have become hugely elongate, most are small and the smallest is about 1.1mm but the largest of all species of the subfamily, at about 9mm, are also included. Clidicini Casey, 1897 includes 2 genera and is Oriental and Australian, The Western Palaearctic Leptomastacini Casey, 1897 includes 3 genera and 20 species, 17 species of 2 genera are European while 3 species of a further genus are known from Turkey. The Old-World tribe Mastigini Fleming, 1821 includes species from the Palaearctic region and South Africa, they are unusual as some are strikingly bicoloured and have diurnal lifestyles in trees and shrubs, 5 species of the single genus Palaeostigus Newton, 1998 occur in parts of southern Europe. Papusini Jaloszyński & Brunke, 2018 includes the single genus New World genus Papusus Casey, 1897, species are diurnal and active in the warmest parts of the year, they occur in deserts, tropical rainforests and caves.
The morphology varies widely but with a little experience most will be readily recognized; they are elongate to broadly oval, often strongly constricted between the head and pronotum and the pronotum and elytra, all are small <4mm, and many are tiny, between 1.0 and 1.5mm, among the European fauna from 0.7 to 2.3mm. The head structure varies but in most it is short to quadrate and oval, usually with long temples which are either angled or converge into a narrow neck, the antennae are placed in front of the eyes and may be adjacent to widely separated, 11-segmented with a variable (and sometimes undeveloped) 3-segmented club, the maxillary palpi are 4-segmented, often well-developed with the third segment enlarged and the fourth small, the labial palpi are 3-segmented and vary widely in form, the mandibles are triangular, robust and lack subapical teeth and the mentum is usually large and well-developed. The eyes vary from large, occupying the whole side of the head e.g. in some Scydmoraphes Reitter, 1891, to very small as in some Euconnus Thomson, C.G., 1859 where the temples are correspondingly large, and in some subterranean forms they are missing. The pronotum is generally quadrate to weakly transverse or elongate, flattened to strongly convex, broadest about the base or the middle and wider than the head, in most it is substantially smooth but for various basal fovea or impressions. Prosternum very varied but often quadrate to very narrow in front of round and contiguous coxal cavities which are open across the base. Mesosternum short and raised, often bearing longitudinal carinae which separate round or oval and closed coxal cavities. Metasternum broad and long, sometimes excavate or carinate medially, the coxal cavities round to transverse and contiguous to widely separated. The scutellum is small and usually visible. The elytra are entire, covering the abdomen or leaving only the pygidium exposed, convex and usually smooth, often with basal impressions but lacking striae, the epipleura are smoothly reflexed and not delimited from the lateral margin by a border. In most the elytral apices are smoothly and continuously rounded but in a few they are truncate and in a very few the elytra are fused. The hind wings are variously developed but in many they are large and functional. The legs vary widely but are usually robust; the tarsi are 5-segmented. Abdomen with six ventrites, their apical margins usually straight or only weakly curved but in strongly arcuate in Scydmaenini. Legs short to moderately long, the procoxae project strongly below the prosternum, the mesocoxae vary; they are convex but usually only weakly projecting and the metacoxae vary from circular to transverse but are usually only weakly convex. Trochanters vary from rounded or triangular to elongate and usually join the femora at an oblique angle. Femora very variable but typically narrow at the base and clavate to almost globose distally, in most they are smooth and unarmed. Tibiae usually long, straight and only weakly broadened towards the apex although in many they are variously curved and flattened, in most genera the pro- and mesotibiae have patches of dense setae towards the apex, and in most the apical spurs are tiny and hardly noticeable. The colouration varies from testaceous to black, many have red markings to the elytra and some are distinctly metallic, all are to some extent, often densely, pubescent. Identification often relies on dissection but even the tiny species have well-sclerotized and robust genitalia. Although many have the typical habitus as described, there is a very wide variation within the group e.g. species of Cephennium Müller & Kunze, 1822 are elongate and smoothly continuous in outline while some Cephennodes Reitter, 1935 are continuous and very broad in form, subterranean forms may be wingless and eyeless, have closely approximated antennal insertions and reduced tarsi. Many species superficially resemble ants, with a constriction between the head and pronotum, and the pronotum and elytra; the association with ants is well documented and about 120 species of 20 genera have been recorded associated with 45 species of ants in 28 genera while about 20 are known from termite nests.
Most species occur in damp environments; among moss and leaf-litter, compost, under stones and among dense vegetation, many are saproxylic; living among decaying fungoid wood and wood debris, and some occur in mammal nests, some are known to feed upon Oribatid mites, with mouthparts adapted to scraping through or cutting the thick mite cuticle. Adults may be obtained from extraction samples of decaying moist wood, moss, leaf-litter, sphagnum and compost, they may also be observed directly when sieving compost etc. and may be collected in flight-interception traps. During the warmest weather they will occasionally occur when sweeping grass or herbaceous vegetation and we have on several occasions obtained them by sweeping around the margins of reed beds.
Although well-represented in temperate regions this subfamily is primarily tropical and subtropical e.g. the Nearctic fauna includes about 220 species of 18 genera while about 500 species of 18 genera occur in Europe. The U.K. fauna includes 32 species in 9 genera and 4 tribes, all of which are very typical of the subfamily; the wider world diversity of some of our genera is surprising: Eutheia Stephens, 1830 includes 35 Eurasian species, Scydmaenus Latreille, 1802 includes >730 species worldwide, Cephennium Müller & Kunze, 1822 includes >130 mostly Palaearctic species, Euconnus Thomson, C.G., 1859 is cosmopolitan with >2500 species and is one of the largest genera in the animal kingdom, and Stenichnus Thomson, C.G., 1859 which is cosmopolitan includes >200 species. Most of our species are rare and of restricted and mostly southern distribution although in general they are infrequently encountered and so likely to be under-recorded. Our two species of Scydmaenus are likely to be found when working compost etc, S. tarsatus Muller, P.W.J.& Kunze, 1822 occurs locally across England and Wales and there are scattered records from Scotland while S. rufus Muller, P.W.J.& Kunze, 1822 is restricted to the south. Stenichnus collaris (Muller, P.W.J.& Kunze, 1822) is probably our most common and widespread species, while two other members of the genus, S. scutellaris (Muller, P.W.J.& Kunze, 1822) and S. bicolor (Denny, 1825) are widespread but very local and S. poweri (Fowler, 1884) is a rare though widespread coastal species. Of our 7 species of Euconnus, only E. hirticollis (Illiger, 1798) is at all common, it is very local across England but much more frequently recorded from Wales, the other species are generally very rare. Our 2 species of Scydmoraphes Reitter, 1891 are widespread across England and Wales but both are very rare. Of our 6 species of Neuraphes Thomson, C.G., 1859, N. elongatulus (Muller, P.W.J.& Kunze, 1822) is widespread and frequently recorded in Wales and the south of England, the others are very local and rare. Cephennium gallicum Ganglbauer, 1899 occurs locally across Wales and the south of England but is generally absent from the West Country. All five UK species of Eutheia are very rare with only a few scattered records from England and Wales.