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.

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Ecology

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.