PSELAPHINAE Latreille, 1802
Includes rarely encountered species that inhabit various decaying vegetation. Some species are associated with ant nests.
This huge and very distinctive group includes more than 12000 described species in >1250 genera, numerous tribes and 6 supertribes, it is cosmopolitan in distribution and by far most diverse in tropical and sub tropical regions but temperate regions tend to have fairly large and diverse faunas; the Nearctic fauna includes > 700 species of > 100 genera and all supertribes are represented, the European fauna includes almost 1000 species of 81 genera and 16 tribes and all supertribes are represented. The UK fauna is poor by comparison with 54 species of 19 genera and 8 tribes representing 5 supertribes. Faunal lists from many tropical regions are relatively small and sometimes involve erratic placements because of lack of research, this is the case in Australia where the species list is small but many hundreds or even thousands of new species need to be named. For many years the group was considered as a distinct family and was only recently incorporated into the Staphylinidae (Newton & Thayer, 1995), the supertribe arrangement is far from settled, many genera remain unplaced and in one case, the Faronitae Reitter, 1882, a tribal system is yet to be worked out.
All species are small, 0.5-5.5mm, although in temperate regions they rarely exceed 3.5mm, and of a characteristic general appearance; they vary from elongate and parallel-sided to broadly-rounded and discontinuous in outline, UK species conform to one or other of these general shapes but in more diverse faunas they form a continuum, most are shiny, drab dark to pale brown and very finely pubescent and in most the elytra are short, leaving the abdomen substantially exposed. Highly modified myrmecophiles differ drastically from the following description and some idea of this can be gained from a consideration of Claviger but many exotic Clavigeritae are much more developed; they are obligate inquilines with often extreme modifications to the body, often with fused segments to the abdomen and antennae to form rigid functional structures and trichomes which secrete solutions on which ants and their larvae feed. They have formed strong associations with ants and some tropical species join columns of ants as they look for prey or new nesting sites. Antennae inserted laterally or anteriorly, 11-segmented in UK species, usually moderately long with thickened basal segments and thickened distally or distinctly clubbed. Head very variable but usually with distinct temples and
© Lech Borowiec http://www.cassidae.uni.wroc.pl/Colpolon/index.htm
© Lech Borowiec http://www.cassidae.uni.wroc.pl/Colpolon/index.htm
small convex eyes, vertex and frons variously impressed and foveate, mandibles well-developed but often small and curved so that they are not visible from above, usually symmetrical and unidentate with several internal subapical teeth, maxillary palpi very variable, the terminal segment is longer than the others and sometimes greatly developed, a feature unique to the subfamily is a tiny appendage inserted into a depression or socket at the apex of the terminal segment, this is intricately sculptured and thought to have a sensory function but is usually not visible with light microscopy. Labrum connected to the clypeus by a narrow membrane, the anterior margin with various peg-like sensilla and the surface with numerous sensory setae. Pronotum quadrate to elongate and rounded or angled laterally, usually with distinct posterior angles but often rounded anteriorly, surface convex or flattened and usually with distinct impressions; a longitudinal impressed line or a central fovea and various sub-basal or lateral fovea. Prosternum long in front of closely approximated and projecting coxae, often with distinct fovea or depressions and usually depressed or with a distinct cavity around the coxae. Mesosternum short and steeply inclined, mesocoxae closely approximated and convex, often placed within a distinct depression or cavity. Metasternum long and convex, often widely excavate anteriorly to accommodate the posterior margin of the meso-coxae and often with distinct median depressions or fovea, meta-coxae closely or widely separated, transverse and weakly to moderately strongly convex. Elytra usually wider than the pronotum, shoulders variously developed but usually broadly-rounded, epipleura variously developed and delimited by a distinct keel; very narrow and hardly reflexed in e.g. Batrisodes but broader and recurved ventrally in Bibloplectus, surface lacking striae but with the sutural margin raised and often with several longitudinal depressions from the base extending into the basal third or half, otherwise often with basal fovea or other depressions, apical margins continuously or separately rounded or truncate. Abdomen usually well-sclerotized, with up to 5 tergites exposed below the elytral margin, segments not fused and always distinct, with various depressions or fovea but never with trichomes, with 6 (females) or 7 (males) sternites in more primitive forms or 5 in more advanced forma as the basal sternite is hidden by the articulation of the posterior coxae and the terminal sternite is atrophied or retracted into the abdomen. In males the terminal sternite forms an operculum surrounding the genital opening. Aedeagus very variable, the median lobe is usually well-developed and often has a translucent dorsal ‘window’, the internal sac often includes well-sclerotized structures and the parameres may be symmetrical, asymmetric or fused medially, in some cases they are atrophied. Legs very variable but usually long and slender with femora substantially visible from above in normal setting. Trocanters usually large and visible in side view, often bulbous and usually obliquely connected to the femora, although in some groups e.g. many Euplectitae they are tiny and hardly visible even from below. Femora long and usually clavate, at least to some extent and sometimes greatly expanded, smooth or (rarely) toothed ventrally. Tibiae very variable; often long, narrow and flattened but sometimes toothed internally or expanded, terminal spurs absent or very small. Tarsi with 2 or 3 simple segments, often with the basal segment very small and hardly visible, in all UK species there is a single claw which is usually large and strongly curved although in many there is an adjacent stiff spine or bristle which gives the impression of a second claw, in many exotic species there are two true claws. Sexual dimorphism is common in the group and males often have more developed antennae or palps, a broader or more strongly sculptured head or pronotum and spurs or spines on various parts of the legs. Identification of the subfamily is usually straightforward to the generic level but often very difficult at the specific level, especially with larger groups such as Euplectus, Bibloplectus or Bryaxis, there is no up to date key to our species in English but the old (1957) RES handbook (available online) remains very useful and there is an essential update by the same author in the Entomologist’s Monthly Magazine (1973, pp.13-26), there is a complete key online HERE based on the German key provided by Arved Lompe HERE which translates reasonably well on google.
The biology of the group is generally only poorly known; larval morphology and adult behaviour and feeding habits have been studied for only a few species, these are mostly common and widespread species from northern temperate regions and so there are likely to be much wider ranges of lifestyles and ecological associations when exotic cavernicoles and desert species are studied, beyond this many are adapted to high altitudes, peat-bogs and maritime habitats etc. and so may lead very different lifestyles. Many species have reduced eyes with large but relatively few facets and well-developed antennae and palps, the majority live in dark habitats and are rarely seen in the open, free-living species are predatory while myrmecophilous species may receive nutrition directly from their hosts or may predate ant larvae or other arthropods within the nest. They are therefore probably tactile predators that rely strongly on chemical stimulation to find prey, and in many of the species studied the main prey items were springtails and mites. They are generally divided into myrmecophilous and free-living species and this works well in northern temperate regions but in warmer parts of the world many species are only occasionally found with ants while others may spend the majority of their life in ant nests. Myrmecophilous species may be ignored by their hosts or they may be accepted and tended by their hosts, being transported about the nest and protected as the ants do with their own larvae, and here there are thought to be complex chemical interactions where pselaphids modify their host behaviour with signalling chemicals. Free-living species generally occur in moist and dark situations among decaying plant material, many occupy woodland habitats, occurring especially among moss and grass etc. growing on fallen timber but also among damp litter and tussocks but are rarely associated with fungi, wetland species tend to occur among marginal litter in shaded situations and some may be found in tussocks and accumulated decaying matter in shallow water. Some species are associated with certain habitats e.g. under certain types of bark, among moss on river banks or among debris in salt marshes and are only rarely found elsewhere. Decaying vegetation and tussocks on field margins may produce abundant specimens and old mammal and bird nests may be productive, compost and manure heaps are often very good, especially where manure and straw are mixed and producing heat through decay.
Among the UK fauna at least 7 species are almost exclusively associated with ants and will rarely be found outside their nests, these are Claviger testaceus Preyssler, 1790, C. longicornis Müller, P.W.J., 1818, Amauronyx maerkelii (Aubé, 1844), Tychobythinus glabratus (Rye, 1870), Batrisodes adnexus (Hampe, 1863), B. delaporti (Aubé, 1833) and B. venustus (Reichenbach, 1816) A wide range of ant species have been recorded as hosts but among the most frequent are Lasius niger (L.), L. flavus (F.), L. mixtus (Nyl.), L. umbratus (Nyl.), L. alienus (Foerster), L. fuliginosus (Lat.), L. brunneus (Lat.), Formica fusca L., F. rufa L., Ponera coarctata (Lat.) and, less often, various species of Myrmica Lat. Other species occur in ant runs and among debris around nests but also occur more generally.
Formica rufa L.
Many, or even most, of our species are regarded as very local and rare but the group no doubt suffers from being under-recorded; they are not often found by general sweeping and are easily overlooked when searching bark or moss etc, the best way to record the, is by taking samples of decaying vegetation, bark or moss etc for extraction and this will often produce abundant specimens. Our 2 species of Bibloporus Thomson, C.G., 1859 occur under bark and are widespread. Our 6 species of Bibloplectus Reitter, 1882 are all very local rare although B. ambiguous (Reichenbach, 1816) can be locally common around the coast of Wales, with the exception of B. minutissimus (Aubé, 1833) which occurs in grass tussocks on riparian fine shingle and sand, all occur in damp moss in wetland situations. Trimium brevicorne (Reichenbach, 1816), Trichonyx sulcicollis (Reichenbach, 1816) and Amauronyx maerkelii (Aubé, 1844) are all very local and rare species associated with decaying timber, the last almost exclusively with various ants. Euplectus Leach, 1817 includes 15 UK species, most of which are very local and rare but a few e.g. E. infirmus Raffray, 1910, E. piceus Motschulsky, 1835, E. sanguineus Denny, 1825 and E. karstenii (Reichenbach, 1816) are widespread and locally common in the south and should soon be found by sampling decaying organic matter and debris from under bark. Our 2 species of Plectophloeus Reitter, 1891 are known from only a few records and both are associated with decaying trees. Of our 2 species of Batrisodes Reitter, 1882, two are very rare and known from a very few southern records while B. venustus (Reichenbach, 1816) is widespread in the south, all are associated with the tree ant, Lasius brunneus (Lat.) in wooded situations. Rybaxis longicornis (Leach, 1817) is locally common among moss and tussocks on wetland margins throughout Wales and England north to Nottingham and eastern parts of Northern Ireland. Of our 8 species of Brachygluta Thomson, C.G., 1859, 4 are very rare and local but B. fossulata (Reichenbach, 1816) and B. haematica (Reichenbach, 1816) are widespread and locally common in the south, including Wales, and B. helferi (Schmidt-Göbel, 1836) and B. waterhousei (Rye, 1869) are locally common in southern coastal habitats, all occur in moss or tussocks in woodland or wetland situations, the last two mentioned species exclusively in salt marshes. Reichenbachia juncorum (Leach, 1817) and Fagniezia impressa (Panzer, 1803) are widespread in England, Wales and the north of Ireland, the former more common and one of the few species likely to be swept from vegetation, both occur in moss and tussocks in wetland situations. Tychobythinus glabratus (Rye, 1870). Tychobythinus glabratus (Rye, 1870) is a very rare species with only a few records from the south east while our 2 species of Bythinus Leach, 1817 are widespread in England and Wales, all are found in wooded habitats, Tychobythinus with ants and Bythinus in moss and tussocks. Our 3 species of Bryaxis Kugelann, 1794 are widespread in England and Wales and among our most frequently encountered members of the subfamily, all occur in tussocks, moss and under bark, often in wooded situations. Tychus niger (Paykull, 1800) is also widespread and common in tussocks in a variety of habitats but T. striola Guilleeau, 1866 is known from only a single old record from Devon. Pselaphus heisei Herbst, 1791 occurs throughout mainland UK and is locally common in the south, especially so in Wales, it occurs in moss and tussocks in wetland areas. Pselaphaulax dresdensis (Herbst, 1791) is a very rare species occurring sporadically across England and Wales, including Anglesey, it occurs in wet moss in bogs and may be common where found. Species of Claviger occur in ant nests, generally with species of Lasius Fab., C. testaceus occurs sporadically across England and Wales while C. longicornis Müller, P.W.J., 1818 is very rare and known from only a few scattered records from South Wales and the Home Counties.