• CATOPOCERINAE Hatch, 1927 includes 2 tribes. Catopocerini Hatch, 1927 includes 3 genera and is mostly Nearctic; the Nearctic genus Pinodytes Horn, 1880 includes more than 40 species, Catopocerus Motschulsky, 1870 includes 5 Nearctic and a single Palaearctic species. Perkovskius Lafer, 1989 includes 2 eastern Palaearctic species. Glacicavicolini Westcott, 1968 includes the monotypic Glacicavicola, see above. Members are commonly referred to as flightless blind beetles and, with the exception of Glacicavicola, occur in the soil or among deep leaf-litter, they are small beetles <4mm, lacking pigment, wingless and blind and most occur in cool and moist temperate forest environments, both adults and larvae are thought to develop among subterranean fungi. Adults are glabrous or nearly so, have a flattened and widely transverse head, generally about 0.5X the pronotal width, which lacks an occipital crest, 11-segmented antennae with the eighth segment reduced, and 5-segmented tarsi.

• COLONINAE Horn, 1880. This is a diverse and virtually cosmopolitan subfamily including 2 genera and about 150 species. Colonellus Szymczakowski, 1964 includes 4 species in 2 subgenera and is restricted to the Oriental region. Colon Herbst, 1797 includes more than 140 species in 9 subgenera and is most diverse in the Western Palaearctic region with about 50 species of which 43 occur in Europe (including Caucasus), about 10 have been recorded from the Eastern Palaearctic and 11 from the Oriental region and 42 species occur in the Nearctic. By comparison southern regions are only poorly represented; 8 species occur in Australia and 1 in New Zealand, 8 in South Africa and 14 in tropical Africa and only 5 from the Neotropics. The UK fauna includes 9 species of 3 subgenera. All species are small <5mm and narrowly elongate oval, continuous or discontinuous in outline and drab, black or variously brown in colour and very finely pubescent. The head is transverse and generally small compared with the pronotum, it is often substantially retracted into the thorax, has well developed, large and convex eyes and lacks an occipital crest, the antennae are 11-segmented with a compact and gradual 4- or 5-segmented club; the eighth segment is usually narrower than the ninth but wider than the seventh. In most the pronotum and elytra are separately convex and in many the pronotum is as wide as or wider than the elytra. The elytra usually lack distinct striae but have a well-impressed and weakly punctured or impunctate sutural striae, any punctation is tiny and generally lost among strong, often transversely rugose, microsculpture. In some subgenera one or both sexes have toothed meta-tibiae and species in general exhibit various sexually dimorphic characters; in many the male has 5 visible abdominal ventrites and the female has 4. Identification can be very difficult and in many the males will need to be dissected and females named by association or comparison. In general the species are collected rather randomly by sweeping or flight interception in woodland, grassland or wooded pasture, and in the UK at least most are rare and of restricted distribution.

• PLATYPSYLLINAE Ritsema, 1869. This small subfamily of highly specialized beetles, commonly referred to as Mammal-nest beetles, includes 4 genera and about 15 species and is restricted to the northern hemisphere. Leptinillus Horn, 1882 includes 1 or 2 species associated with beavers nests and is widely distributed. Platypsyllus Ritsema, 1869 includes a single species of Beaver ectoparasite, restricted to North America, northern Europe and Asia. It is a very unusual beetle; eyeless, wingless and resembling a flea or a louse with short and broad antennae partly enclosed in a modified basal segment. The larvae also live on beavers, having modified hook-like thoracic segments which allow them to cling to the host. Both adults and larvae feed on skin tissue and secretions and it is thought the larvae may also be scavengers inside the lodge; it is the most highly specialized member of the subfamily with all stages except the pupa developing upon the host.  Leptinus Mueller, 1817 includes 9 species and is Nearctic (3 spp.) and western Palaearctic in distribution. They are commonly known as Mammal-nest Beetles and have been recorded from a wide range of species, mostly rodents, and also occasionally from nests of social insects. They are more typical of the family, resembling the following two subfamilies but lacking eyes and having filiform or gently widened antennae without a modified eighth segment. A single species L. testaceous Muller, P.W.J., 1817, is widespread though very local in the UK. Silphopsyllus Olsufiev, 1923 includes a single Eurasian species, S. desmaniae (Olsufiev, 1923), a rather typical, entirely pale testaceous leiodid with gradually thickened, almost filiform antennae, an occipital ridge and several impressed longitudinal striae to the slightly transverse elytra and, like other members of the subfamily, lacking eyes. It is an ectoparasite of the aquatic insectivorous mammal Desmana moschata Güldenstädt, 1777.

• LEIODINAE Fleming, 1821 is a large, near cosmopolitan group of about 60 genera included in 6 tribes although variations in this classification will occur in the literature. The largest tribe, Agathidiini Westwood, 1838 includes about 11 genera and 950 species and is most diverse in the Oriental region with more than 550 species. Because of this tribal diversity the Oriental region is the most diverse for the subfamily as a whole but most northern temperate regions are well-represented; about 150 species of 16 genera and 5 tribes occur in the Nearctic, more than 230 species of 19 genera and 5 tribes are recorded from the western Palaearctic and about 175 species of 24 genera and 5 subfamilies from the eastern Palaearctic. Southern hemisphere regions are generally much less diverse; about 100 species of 20 genera and 6 tribes are Neotropical, 4 genera and about 20 species are recorded from each of Australia and New Zealand, and the Pacific fauna includes 6 genera and about 30 species. At least 2 genera and 5 species from 2 tribes are known from Madagascar and these represent the only Leiodidae recorded there although the South African fauna includes 10 species of 7 genera and 5 tribes and that of tropical Africa includes 40 species of 13 genera and 5 tribes. The Neotropical fauna is similarly poor with about 100 species of <20 genera in 5 tribes. While most tribes are widespread, the monogeneric Estadiini Portevin, 1914 is restricted to Australia (3 spp.), tropical Africa (2 spp.) and South America (1 sp.). The UK fauna includes 49 species of 10 genera and 4 tribes; they are distinguished among the family by the combination of a loose 3- or 5-segmented antennal club and the lack of an occipital ridge. Most members are elongate oval and convex although some, most notably many species of the large genus Agathidium Panzer, 1797, are almost circular in outline, the form of the eighth antennomere varies, in many it is smaller than adjacent segments but in some e.g.  the Holarctic Triarthron Märkel, 1840 they are equal or nearly so. As with most of the family, many species are drab brown or black but some Agathidiini (especially) are distinctly patterned or bicoloured. The biology is generally poorly understood but Agathidiini are thought to develop in Myxomycetes while others are associated with subterranean fungi. Sampling tends to be rather random; many can be found by general sweeping, especially in wooded or calcareous grassland habitats, pitfall trapping and extracting fungus samples or by flight-interception trapping and many are crepuscular or nocturnal.

• CHOLEVINAE Kirby, 1837. This is the largest subfamily and is classified into 7 tribes; it is near-cosmopolitan in distribution with by far the greatest diversity in the Western Palaearctic with almost 200 genera and more than 1100 species, the Eastern Palaearctic fauna includes about 30 genera and a little more than 110 species, the Oriental region is also less diverse with about 20 genera and 170 species. Oritocatopini Jeannel, 1936 is a small group of 3 genera and about 20 species and is restricted to tropical and southern Africa. Anemadini Hatch, 1928 is a large group of 25 genera and almost 300 species; it is Holarctic with a single genus in South America and is the only tribe within the subfamily to occur in Australasia or the Pacific islands. A single species, Nemadus colonoides (Kraatz, 1851), occurs in the UK. The monogeneric Eucatopini Jeannel, 1921 includes about 15 species of Eucatops Portevin, 1903 and is restricted to the Neotropical region. Leptodirini Lacordaire, 1854 is the largest tribe, although the limits will be found to vary, with about 180 genera and more than 800 species, it is Holarctic in distribution extending south into West Africa although only 2 species of a single genus occur in the Nearctic region and very few are recorded from the Eastern Palaearctic and Oriental regions, it is essentially a western and central Palaearctic group e.g. about 180 species occur west of the Pyrenees, but is not represented in the UK ( although Parabathyscia Jeannel, 1908 is included). Species are subterranean, lacking pigment and with reduced eyes etc. and are among the most speciose groups of subterranean beetles. At least 7 subtribes are recognized, some of which are restricted to certain areas e.g. the monogeneric Spelaeobatina Guéorguiev, 1974 from southeast Europe, or Bathysciotina Guéorguiev, 1974 with6 genera from central and northern Europe, the monogeneric Platycholeina Horn, 1880 is Nearctic. The largest subtribe, Leptodirina Lacordaire, 1854, is more generally distributed and represents the geographical limits for the tribe. The monogeneric Sciaphyini Perreau, 2000 includes 2 species from eastern Asia. The remaining tribes, Ptomaphagini Jeannel, 1911, Cholevini Kirby, 1837 are well represented in the Holarctic region generally, including the UK, and are typical of the family generally with elongate-oval and rather flattened body and a distinct occipital crest before the anterior pronotal margin. Species of these 2 tribes are among the most collected as they occur in decaying organic material e.g. mammal nests, dung, leaf-litter, carrion and fungi, and in the spring will often occur by general sweeping or in numbers in baited pitfall traps. Many are associated with fungal fruiting bodies and so will occur when sampling decaying timber.

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Ecology

Although morphologically diverse various members of Platypsyllinae are very specialized ectoparasites as adults and larvae, and perhaps scavengers also as larvae, on a range of aquatic or mostly aquatic mammals, feeding upon the secretions, dead skin and perhaps blood of the host, the associations of Leptinus are more general where each species may occur in the nests of a range of mammals as well as those of social insects such as bees, ants and termites. This wider association is also seen in some members of other tribes such as Ptomaphagini, Cholevini and Anemadini, and such specialization may be recent and opportunistic as species within a genus may display a range of feeding habits and lifestyles. Leiodid feeding preferences otherwise fall into 2 broad categories; saprophages and mycophages, although in the former case many species are thought to consume mycelia and spores etc. within various habitats. Saprophagous species develop in decaying organic matter such as leaf-litter, compost, dung and carrion, and such habitats may produce large numbers of adults at the right time e.g. some Catops may occur in large numbers under recent avian carcasses. The same association is seen in cave dwelling and subterranean species e.g. Catopocerinae generally or members of the large genus Parabathyscia Jeannel, 1908, where development occurs among decaying organic matter and the fungi associated with such, these species generally emerge only for brief periods and at specific seasons to disperse and so are seldom seen and sampling tends to include more luck than judgement. Mycophagous species occur either upon mycelia or fruiting bodies on decaying wood etc. above ground, or among subterranean fruiting bodies etc. Terrestrial species may be sampled using various extraction techniques on suitable material, by flight-interception traps or by searching suitable habitats, especially by night when many species are active. Subterranean traps are often successful but, like flight-interception trap, will need to be left in a safe place for some time. About half of all leiodids are flightless and these include the majority of subterranean species occurring among organic material and many of those inhabiting leaf-litter, nests and caves etc. and so will need to be researched on an individual basis in order to find them. Many of the species developing in ephemeral habitats such as fungi, subterranean or otherwise, dung and carrion are fully winged and capable of flight and will be found by sweeping, trapping and searching generally at the time of dispersal. The life cycles are generally only poorly understood but development from egg to adult is usually rapid and adults are long-lived, eggs develop rapidly and larvae mostly pass through 3 instars, in species developing in ephemeral habitats this can take only a few days but in e.g. Leptinus, which are closely associated with a mammalian host, there are 5 instars and development takes longer. In some cave-dwelling species there are only 1 or 2 instars and development may take weeks or months.

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Description

So far as the UK fauna is concerned most species have a reduced eighth antennomere and may be recognized by this character alone, although leiodids are a fairly distinct group which will soon become obvious.

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Small to medium sized beetles, 1-8mm, very variable in shape and convexity from almost hemispherical and continuous in outline to very elongate, discontinuous and variously flattened. Most are drab, black to various shades of brown or bicoloured with contrasting forebody and elytra or, in a few species, with pale macula to the elytra. Head variable from flat and produced anteriorly to convex and strongly declined, eyes entire and usually convex and prominent, reduced or absent in many subterranean and parasitic species, temples usually short and constricted to a short neck although both are often hidden within the prothorax. Vertex and frons simply convex and without structure, labrum transverse and evenly rounded anteriorly to emarginate or deeply bilobed. Mandibles symmetrical or asymmetrical with a well-developed apical tooth and, in many, with a large molar towards the base, maxillary palps 4-segmented with segments equal in width and the terminal segment usually the longest, rarely reduced or modified, labial palps 3-segmented with segments equal or with segments 2 and 3 enlarged or reduced. Antennal insertions in front of or between the eyes, generally visible from above or sometimes concealed below a lateral expansion of the clypeus, in some with antennal grooves below the eyes. Antennae usually relatively long, 11-segmented or, rarely, 10-segmented, with a 3-5 segmented gradual or abrupt club, generally with segment 8 smaller than 7 and 9, in some gradually thickened distally or from the base to the apex, or rarely simply filiform. Pronotum generally transverse, rounded laterally and widest about the middle or towards the base, from rather flat to moderately or very strongly convex, without structure or with simple basal fovea, in some species that are capable of rolling into a ball the anterior margin is emarginate to receive the explanate margin of the head and form a continuous outline. Lateral margin smoothly convex and finely bordered, usually simple but in some species finely crenulate. Prosternum variable in length anterior to round or transverse and open or closed coxal cavities, the process separate from or fused to a post-coxal process, variable and sometimes extending to the anterior margin of the mesosternum in which case the coxae are recessed to accommodate the process; sometimes with distinctive longitudinal carinae or dilated over the coxae. Mesosternum with a transverse anterior carina and a variously developed median longitudinal carina, and often produced posteriorly to an acute process between the mesocoxae or otherwise modified. Mesocoxal cavities round or transverse and usually continuous or only narrowly separated. Metasternum generally short, with a raised keel posterior to the meso-coxae and a transverse suture anterior to the meta-coxae, and narrowly raised posteriorly, the central area flat or weakly convex, in many produced forward to meet the mesonotum between the meso-coxae. Metepisterna sometimes with a groove or otherwise modified to retain the elytral epipleura. Meta-coxae transverse and contiguous or only narrowly separated. Scutellum usually well-developed and elongate-triangular or with curved margins. Elytra usually completely covering the abdomen or leaving only the pygidium or propygidium exposed, continuously or separately rounded apically or, rarely, truncate, abbreviated in some parasitic forms. Surface smooth or finely punctured and usually microsculptured; sometimes with transverse striations, and often with impressed striae or rows of larger punctures. Ventral elytral surface sometimes with discreet areas of small teeth opposite modified areas of the abdominal tergites, and sometimes modified laterally to interlock with lateral parts of the thorax. Legs very variable, in some (non-UK) strongly fossorial, but generally long and slender, not retractile but in many the coxae or femora are grooved posteriorly, femora smooth or with ventral teeth and often sexually dimorphic, tibiae slender and smooth or broadened apically and with strong spines externally, in many groups dimorphic. Tarsi very variable; from 5-5-5 to 3-3-3 and sometimes with heteromerous combinations and sometimes sexually dimorphic, all segments usually obvious and without widely lobed or otherwise modified segments, at least in non-parasitic and terrestrial species, claws usually simple and relatively large.