OXYTELINAE Fleming, 1821
These small rove beetles are found in almost any habitat, and are often among the most abundant insects among decaying organic matter.
Our UK fauna is relatively diverse with 15 genera representing 7 tribes and in various situations they are among our most common staphylinid species. In general they are associated with decaying vegetation, fungi and dung in a very wide range of habitats although several genera e.g. Carpelimus and Thinobius, are more or less confined to wetland marginal situations and members of Bledius are unusual in that they construct brood burrows in marginal sediments. The majority of species are of a very distinctive elongate and parallel-sided form which, coupled with the following characters, makes them readily identifiable. The antennae are inserted laterally ; outside the outer margin of the mandibles and usually near the anterior margin of the eyes, they lack long outstanding setae and may be broadened towards the apex but are never clubbed, in most the insertions are concealed from above beneath expanded lateral margins of the clypeus. The quadrate to transverse and usually flat or only weakly convex, usually with distinct temples and often produced anteriorly, the eyes vary widely in size and convexity; in some Carpelimus occupying almost all the lateral margin, a condition seen in e.g. Steninae but they are otherwise abundantly different. The labial palps are normally developed with the terminal segment cylindrical and tapering or truncate, never expanded as in e.g. Oxyporinae. In many there are depressions or elevated margins etc. to the vertex and clypeus and these may be sexually dimorphic, but they always lack ocelli and are never so extremely developed as in Piestinae. The pronotum is quadrate to transverse, as wide as the head and generally narrower than the base of the elytra, the dorsal surface often has prominent longitudinal furrows or other depressions etc. which are generally diagnostic for genera and many species, in some Bledius the male pronotum is hugely developed into an anterior facing horn-like structure. The elytra are smoothly convex, lacking longitudinal ridges, transverse to elongate with distinct shoulders and at least as wide as the pronotum. In most the head, pronotum and elytra are randomly punctured; the elytra may be striate but this is rare among our fauna, and most are finely pubescent; some wetland species are densely pubescent and some dung inhabiting species are virtually glabrous. Most are drab black to dark brown with variously paler appendages but some are bicoloured, dark with pale elytra. The legs are robust and moderately long, in most the anterior
and middle tibiae have one or two rows of robust setae or spines along the outer margin, and the tarsi are three or five segmented. Species of Paederinae have similar lateral antennal insertions and some may be mistaken for the present group but here the pronotum is usually distinctly elongate and where this is not the case the head is attached to the prothorax by a narrow neck, and all species lack the series of stiff setae or spines to the anterior tibiae. This key to the UK genera will serve to show various aspects of oxyteline morphology.
Identification within this subfamily is often problematic but most of the larger and more common species are straightforward which should make the group attractive for collectors and recorders, especially as they are easily sampled and good series are easy to make up. Sexual dimorphism is common and often extreme e.g. in some Platystethus and Bledius, and very useful in identification work. Some of the smaller species as well as e.g. some Bledius, on the other hand can be very difficult to identify, will need to be dissected and females assigned by association, this is very difficult at first as the material is small and delicate but we are fortunate in having a superb guide in the form of the 2009 RES handbook by Derek Lott, this includes all the advice needed to deal with the majority of our list and the 2018 checklist can be used for guidance. Earlier works are now so dated as to be useless for the larger genera.
Deleaster dichrous (Gravenhorst, 1802). This is our only species of a widespread Holarctic and Afrotropical genus. It is a large and distinctive beetle; 7-8mm with a dark head and abdomen and an orange pronotum, elytra and appendages; the shape is reminiscent of several omaliine species e.g. Anthophagus Gravenhorst, 1802 or Lesteva Latreille, 1797 but distinguished by the lack of ocelli, and it is otherwise atypical among our fauna due to the general habitus. It is widespread and locally common across western and northern England and Wales and more local and sporadic in the southeast and the north of Scotland. Adults occur through the spring and summer; they are generally associated with riparian sediments, often in shaded situations, fly well and sometimes occur at light.
Coprophilus striatulus (Fabricius, 1792) is our only species of a widespread Holarctic genus. Adults are large, 6-7mm and entirely dark with pale appendages and margins to the pronotum, elytra and abdomen, it is distinctive by the form of the pronotum; the lateral margins are finely crenulate and the disc has a median longitudinal depression which becomes a ridge towards the base separating two oblique oval depressions. It is a local species of southeast and central England and Wales, becoming very local and rare further north, generally associated with wetland environments. Adults are active in early spring and when they disperse by flight. In North America where it is a widespread adventive from Europe it occurs in a wider range of habitats; decaying organic material including dung, carrion and at sap, under deciduous bark and, in the winter, among mammal nests.
Syntomium aeneum (Muller, 1821) is our only species of a widespread Holarctic genus, with the exception of the West Country it is locally distributed throughout England and Wales and there are a few scattered records from Scotland. Adults are quite distinctive; entirely dark with a metallic lustre, paler appendages and very strongly microsculptured abdominal tergites, the forebody is strongly punctured and finely pubescent, the pronotum is strongly transverse with crenulate margins and sinuate towards the base, the elytra are transverse with the basal margin widely arcuate. The typical habitat is open dry areas with patchy vegetation, especially in upland areas.
Anotylus Thomson, C.G., 1859 includes 14 UK species, they are very similar to Oxytelus and were formerly included in that genus but differ most obviously by the form of the scutellum, more subtly the basal antennomere is gradually expanded from the base and almost triangular in shape. The species vary widely in size and detail e.g. microsculpture and punctation but all are parallel-sided, flat and rather wide insects, the forebody is glabrous but for various sensory setae and the abdomen is usually sparsely clothed with short setae. They are generally associated with decaying organic matter, especially dung, in a very wide range of habitats although some are more specialist e.g. A. maritimus Thomson, C.G., 1862 occurs on beaches throughout the UK and A. saulcyi (Pandellé, 1867) is associated with subterranean mammal nests. Some e.g. A. tetracarinatus (Block, 1799) are among our most common staph species on dung pasture.
Oxytelus Gravenhorst, 1806 includes 5 species of 3 subgenera. Superficially very similar to Anotylus but having a triangular scutellum and the basal antennomere either constricted subapically or only very weakly broadened towards the apex. They are associated with decaying organic matter and are among the most common staphs on dung pasture although the widespread but rare O. fulvipes Erichson, 1839 occurs in wetland habitats. Adults may occur through the year and may be found in any situation where there is suitable host material, they fly well and are attracted to light; in the spring and summer they occasionally swarm on warm evenings and may be swept in large numbers.
Bledius Leach, 1819. Our UK list includes 27 species of 7 subgenera. Species are very distinctive due to the general form and the 2 series of robust spines along the outer and inner margins of the pro- and mesotibiae. Of all the oxyteline species these are the most adapted to a burrowing mode of life; the pedunculate attachment of the prothorax to the mesothorax allows the body to turn inside burrows and field observations suggest the mandibles are used for excavating in fine sediments. The dorsal surface is convex and usually strongly microsculptured and pubescent and in all our species the first antennomere is very long compared to the others, but otherwise they are readily recognized as members of the subfamily. Sexual dimorphism is usually obvious with the head and pronotum variously developed males, in some species e.g. B. spectabilis Kraatz, 1857 spectacularly so, and in some the margins of the ninth tergite are emarginate or furnished with spines. Most species occur on wetland margins where they form brood burrows in sandy or clay substrates although some may also be found in sandy locations away from water. Many occur in large colonies which, with a little experience, may be detected by small mounds of sediment cast out from the burrows, and many disperse by flight and may be found swarming or at light. Adults and larvae feed on algae and some species display parental care with the adults provisioning burrows with larval food. Burrows are usually waterproof, at least to some extent, and can be made so by the adults from within and so may occur in areas with fluctuating water levels, this is exemplified by coastal species which live within the intertidal zone. Unfortunately while the majority of species occur in colonies and so may be locally abundant most are very local or rare and of restricted distribution.
Platystethus Mannerheim, 1830 includes 7 species in 2 subgenera. Our only species of Platystethus s.str., P. arenarius (Geoffroy in Fourcroy, 1785) is a common species of dung pasture and decaying organic matter generally. With a single exception our species of Craetopycrus Tottenham, 1939 occur in wetland situations; P. capito Heer, 1839 occurs among vegetation on dry chalk and limestone areas in the south. Members are readily distinguished by the central longitudinal channel and rounded form of the pronotum.
Aploderus Stephens, 1833. Our single species is very distinctive due to the form of the pronotal sculpture, see above, otherwise it is very characteristic of much of the family and might be mistaken for an Anotylus or Oxytelus; it is parallel-sided and flat, the body is dark and the elytra and appendages pale. Formerly more widespread it seems to have declined in recent decades and is now very local in the southeast; it is associated with decaying vegetation and dung.
Carpelimus Leach, 1819 includes 22 species of 4 subgenera. Although rather nondescript these beetles are readily identified to the generic level by the form of the pronotum and elytra and in the field they soon become familiar due to the small size, flattened and parallel form and short legs. They are mostly wetland species occurring among marginal litter and decaying vegetation in a wide range of habitats from shady woodland to river banks, exposed heathland pools and reedbeds etc., and some are restricted to saline conditions. In marginal situations they may occur in large numbers and several species are often found together but some common species e.g. C. pusillus (Gravenhorst, 1802) or C. bilineatus Stephens, 1834 may also occur more generally among decaying vegetation away from water. Sweeping marginal vegetation or sifting through litter will invariably produce them; they also swarm in the evening and may occur at light in large numbers.
Thinodromus Kraatz, 1857. Our single species, T. arcuatus (Stephens, 1834), was formerly included in Carpelimus and is closely similar but the form of the pronotal depressions is distinctive. It is a widespread species, though generally scarce in many eastern areas, of exposed sediments beside rivers and streams.
Manda Blackwelder, 1952 includes the single very distinctive species M. mandibularis (Gyllenhal, 1827); it is a large pale brown insect with a black head and a series of four incomplete longitudinal ridges to each elytron. The typical habitat is among vegetation around woodland ponds and while it may be common where it occurs it seems to have declined recently and the only modern records are from Sussex and Gloucestershire.
Ochthephilus Mulsant & Rey, 1856. Our 4 species are readily recognized by the pronotal sculpture and the long and broad elytra which are reminiscent of various Omaliinae. All are associated with the margins of streams and rivers and all are very local though widespread; mostly in western and northern areas.
Planeustomus Jacquelin du Val, 1857. Includes 2 very rare species recorded from the southeast, adults are associated with leaf litter and organic debris in damp situations and, at least in one case, are known to disperse by flight. They are very distinctive beetles and should not be confused with any other; elongate and narrow with a large head, pronotum broadest near the anterior margin and narrowed to the posterior angles and striate elytra are unique among our fauna.
Teropalpus Solier, 1849 includes a single species, T. unicolor (Sharp, 1900) which was introduced in the 19th century; it occurs under seaweed on sandy beaches and is widespread in the south.
Thinobius Kiesenwetter, 1844 includes 7 species, all associated with sparsely vegetated shingle and fine sediments beside streams and rivers. Most occur in western or northern areas and are very local or rare although they may be common where they occur. They are very difficult to record due to the small size, they are the smallest species of the subfamily in the UK, and habitat which is among submerged sediments and often only in particular areas of a more extensive environment, adults disperse by flight and may swarm but beyond this the habitat will need to be worked carefully to find them. They superficially resemble other tiny oxyteline staphs but the smooth pronotum is diagnostic.