HISTERIDAE Gyllenhal, 1808
This family can be found in a wide range of habitats, from dung and compost to dead wood, both diurnally and nocturnally. Many species are widespread, and often abundant.
POLYPHAGA Emery, 1886
HYDROPHILOIDEA Latreille, 1802
The Histeridae is a cosmopolitan family of more than 4200 species included in 11 subfamilies and about 390 genera. As with most larger families the classification is not fully worked out and may change. The family is well represented in the Palaearctic region, and in Europe more than 100 species represent 7 subfamilies. Diversity increases towards the tropics; about 450 species and 60 genera occur in the U.S.A. whereas there are more than 1000 Neotropical species representing about 140 genera. The adults are diverse in form ranging from very convex and almost circular in outline to flattened, elongate and parallel sided; the two basic forms are oval and convex, and long and parallel, but there are many variations on these themes. Some species exhibit exaggerated morphology e.g. in the Central American genus Trypaneus the thorax is very elongate, about twice the length of the elytra. Despite this the members have a certain overall form that soon becomes obvious whatever the size and shape. The size ranges from around 1mm to more than 10mm in some Histerinae and Abraeinae (Teretriini). Most species are heavily sclerotized and robust. The surface sculpture varies widely from smooth to heavily sculptured, and from glabrous to pubescent or scaled. The majority are drab, especially the smaller ones; black or various shades of brown, while many larger species are dark with bright red, yellow or green patterns or markings. Some species are metallic. The elytra are often (usually) truncate and almost always shorter than the abdomen, generally leaving two tergites, the pygidium and the propygidium, exposed. Most have specialized heads that can be retracted into or under the prothorax. The antennae are 9 to 11 segmented with a scape as long as, or even longer than, the funiculus. The scape is distinctive and will often serve to identify a specimen to the family; long, usually curved and broadened towards the apex, and square, or at least in part angular in cross-section. They are usually distinctly clubbed or, rarely, broadened towards the apex. The prosternum has cavities for the reception of the antennae when the beetle is ‘rolled up’, these are either anterior, behind the front margin, or posterior, and their position is often a useful aid in identification. Where elytral striae are present they tend to be abbreviated or incomplete; the numbering of the striae for reference (Fig 1) is different to that used for most beetles where the sutural stria is counted
as the first. The legs are generally flattened and so add to a smooth outline when the beetle is rolled up. The tibiae, especially the front pair, are often dilated and toothed on the outer margin, in larger species these teeth are large and aid the beetle in digging through the host medium. The tarsal formula is usually 5-5-5; only in some Abraeinae does it vary to 5-5-4.
Many of the larger and more conspicuous species can be found in decomposing vegetation, in dung, or at carrion where they feed on the early stages of other insects. Histerids generally arrive late at carrion and dung, after other species have colonized the habitat, so that a food source is available. Species associated with fungi or saproxylic lifestyles tend to be smaller and may occur in large numbers. Many are nocturnal and the majority, if not all, of histerids can fly well. At least some species can be found throughout the year. The majority of species are active nocturnally. Some live in the nests and burrows of other animals; some in mammal and avian nests, and many others are associated with social insects (Hymenoptera) or the burrows of other saproxylics. Two groups, Hetaeriinae and Chlamydopsinae, are exclusively mymecophilus. It is likely that the vast majority, if not all species, are predaceous.
The British list contains just over 50 species in 7 of the 11 subfamilies and is varied enough to represent the family as a whole; it includes members of all the ecological groups. Several species have been added in recent decades.
Because the subfamilies display various forms and lifestyles they are described separately, and briefly, below.
ABRAEINAE MacLeay, 1819
Worldwide about 500 species have been described. Most are associated with decaying vegetation or are saproxylic while some occur in litter and a few in ants’ nests. So far as is known all are predaceous. Many species are small, <2mm, and so the subfamily is often referred to as microhisteridae. Inculdes 5 or 6 tribes depending on whether the Trypanaeinae is considered as a separate group or a sub-group, as seems likely, of the present subfamily, of which 4 occur in the U.K. and are represented by 9 species. All British species are small, 1-2.5mm, most are convex and smooth, without or with only rudimentary elytral striae. Plegaderus species have deeply impressed lines on the pronotum. Most are predatory, living in decaying wood or vegetation while some, Aeletes and Teretrius, are adapted to live in the galleries of other saproxylic insects. Two species, Aeletes atomarius (Aube) and Abraeus granulum Er. are sometimes associated with the ant Lasius brunneus. Acritus nigricornis (Hoffman,J.) has been recorded from a rats nest. Halacritus punctum (Aubé) occurs only under decaying seaweed and debris above the high tide line. Teretrius fabricii Mazur, last recorded in 1936 and now considered extinct in the U.K, is a predator of Lyctus larvae.
CHLAMYDOPSINAE Bickhardt, 1914
Includes 13 genera and around 140 species. The majority of described species are from Australia although they are known from Oceania north to Japan and from India. They are small, convex and broadly elongate beetles. Many have a strongly sculptured and punctured dorsal surface, and some show exaggerated features of the head, pronotum and elytra. In most species the scutellum is hidden by a basal expansion of the pronotum. The species are recognised by the form of the antennae, the insertion of which is placed above the eyes, high on the frons, the scape is often greatly expanded so that it covers the eye when the head is withdrawn (chlamydopsis means ‘covered eye’). All species are myrmecophilus and, with the exception of 5 species of Ceratohister Reichensperger, 1924, possess trichomes (well developed secretory structures) either on the pronotum or on the humeral areas of the elytra.
TRIBALINAE Bickhardt, 1914
This is a small subfamily of about 200 species included in 11 genera. Many are tiny and convex beetles which are distinct by the form of the prosternum; the process, or lobe, is well developed and extended laterally so closing the antennal cavities from beneath, and is bordered at the base by a distinct presternal suture. This form of prosternal structure is also seen in many Histerinae but the present subfamily is distinguished by the presence of a pair of labral setae which are absent in that group. The subfamily has a worldwide distribution; a single species, first recorded in 1980, occurs in the U.K. Most Neotropical species are saproxylic while in other regions they occupy a wider range of niches including decaying vegetation and dung.
NIPONINAE Fowler, 1912
This subfamily contains a single genus, Niponius Lewis, 1885, of 22 species of elongate and very distinctive Histerids. While there are genera in other subfamilies with a similar overall morphology, species of Niponius are unique in possessing a large, elongate head with produced frontal processes and ventrally deflexed mandibles. All species are specialist predators of other saproxylic coleoptera, either tunnelling under bark or hunting within galleries. Most species are native to Japan but a few occur farther afield, from Northern Austrailia to India.
DENDROPHILINAE Reitter, 1909
This large subfamily includes 4 tribes of which 2 occur in the U.K; Dendrophilini and Paromalini.
ANAPLEINI Olexa, 1982 contains a single genus, Anapleus Horn, 1873, with 15 described species. These are small Histerids, 2-3mm, oval and convex, resembling a large Abraeus. The upper surface is shiny and heavily punctured, and the elytra lack striae. They have an unusual form of prosternal development which is seen elsewhere only in Dendrophilus, which is smaller and has at least some form of elytral striae. Members of the genus occur throughout the Holarctic, but not in the U.K, and several have been found in Mexico.
BACANIINI Kryzhanovskij & Reichardt, 1976 A large tribe of 6 genera and around 100 species with a ‘cosmopolitan’ distribution which does not include the U.K. The overall form is oval to almost round or elongate oval, smooth and finely punctured and, apart from this, rather nondescript. The group is readily recognised by the elytra which are apically rounded and cover the propygidium. Little is known of their biology and many specimens await description.
DENDROPHILINI Reitter, 1909 The limits of this tribe are still to be worked out; it was for a long time considered to include two genera, Dendrophilus Leach, 1817 and Kissister Marsuel, 1862, but now it seems that the latter might be more appropriately placed within the Paromalini. Dendrophilus contains 8 species and has a Holarctic distribution. The species are small, oval and convex with greatly dilated tibiae and a series of almost complete elytral striae. The form of the antennal club is unique to the genus, being inwardly curved (arcuate), in the often closely similar Paromalini it is outwardly curved. Most species are associated with decaying vegetation; compost and litter etc. but some are found in mammalian or avian nests and one species, D. pygmaeus (L.), is myrmecophilous.
PAROMALINI Reitter, 1909 A worldwide tribe containing 13 genera of mostly saproxylic species. Many occur under bark and some North American species of Carcinops Marseul, 1855 are associated with cacti. All Neotropical species are saproxylic. In Cuba several species of Carcinops occur in caves. The widespread C. pumilo (Erichson, 1834) occurs among rotting vegetation and dung. Most species are small <4mm, and drab coloured although some are metallic green or blue, elongate oval or slightly flattened. Species of Platylomalus Cooman, 1948, a worldwide genus of about 60 species, are the exception being elongate, rather parallel sided and flat. Most are smooth, without dorsal sculpture, and have well impressed and punctured elytral striae. Species of this tribe are characterized by the combination of a well developed prosternal lobe which is not dilated to cover the antennal cavities and is notched elaterally to accommodate the large fore-tibial spurs when the beetle is rolled up, the presence of labral setae and the arcuate antennal club.
TRYPANAEINAE Marsuel, 1857
This subfamily is closely related to the Abraeinae and includes 3 genera and around 80 species of highly specialized saproxylic beetles that live in the burrows of other wood boring insects. All occur in the New World and the largest diversity occurs in Middle and South America. They are cylindrical and very elongate, the pronotum is highly developed and generally about twice the elytral length. The elytra are more or less quadrate, leaving very prominent abdominal tergites exposed. The head is produced forward and the tibiae possess large and prominent teeth along the outer edge.
TRYPETICINAE Bickhardt, 1913
A small subfamily of 3 genera; Pygocoelis Lewis, 1897 with 10 species and Trypobius Schmidt, 1893 with 2 species are African while more than 100 species of Trypeticus Marseul, 1864 occur in South East Asia, especially China, and Australia. All species are small and cylindrical with the pronotum and elytra about equal in length. They are drab; mostly dark brown, smooth, shiny and punctured. The clypeus and frons are smooth; without a suture, and the clypeus is prolonged into a ‘snout’. The elytra lack striae, and the propygidium has an oblique striae on each side. Many species exhibit sexual dimorphism. They are saproxylic with many species inhabiting the tunnels of other insects.
SAPRININAE Blanchard, 1845
A large subfamily of more than 620 species included in about 40 genera. They have a worldwide distribution and the Palaearctic region is diverse with at least 270 species included in 33 genera. Many are endemic to the deserts of North Africa and Central Asia. The large genus Saprinus Erichson, 1834 is mostly from the Old World; of more than 160 species only 9 occur in North America. Although they range widely in size, the largest exceed 10mm, the appearance varies little; they are oval and convex above and below with elytra that are variously punctured and striate. The tibiae are usually expanded, sometimes greatly so, and, at least the fore-tibiae, strongly dentate externally. Most are drab; black or dark brown but a few are patterned and some are metallic. Assigning specimens to this subfamily is generally straightforward as they have a distinctive prosternum; the lobe is short and truncate or curved anteriorly, and the antennae retract into cavities either side and remain exposed. The prosternum nearly always has impressed lines, generally longitudinal, on the surface and these often provide useful diagnostic characters for the species. Members occupy a wide range of habitats; carrion and dung are common hosts and many occur in avian and mammal nests and burrows. Some species are myrmecophilous. Several Saprinus species are specialist predators on other insects among foliage etc. Species are especially numerous in sandy habitats, some occur generally on inland dunes etc. while others are restricted to the coast; Hypocaccus Thomson, C.G., 1867 species occur on beaches throughout the world.
HAETERIINAE Marseul, 1857
A worldwide subfamily containing 3 tribes and about 110 genera of small and highly specialized myrmecophilous and termitophilous species. About 30 species occur in the Palaearctic and Nearctic regions, and the group is particularly diverse in the Neotropical region. They live within the nests, consuming ants etc. and their immature stages. Many species are rather quadrate and smooth with distinct, if sparse, pubescence which often forms rows on the elytra. In some the elytra are glabrous. All are very distinctive in appearance, even the elongate tropical species, and are readily recognized; most are drab, dark to pale brown or almost yellow, with a squat, convex body and long legs with dilated tibiae (especially the middle pair) and well developed tarsi. The pro-tibiae lack apical spurs. The antennal scape is short and dilated, usually almost triangular. The prosternal lobe is extended laterally to partially cover the antennal cavities located behind the front angles. The elytra are often striate, sometimes smooth.
HISTERINAE Gyllenhal, 1808
The Histerinae contains 5 tribes and more than half of all known species of the family. It has a worldwide distribution and contains many of the larger and frequently encountered species e.g. Hister Linnaeus, 1758 and Margarinotus Marseul, 1854. Several of the genera are very large and widely distributed e.g. Hister Linnaeus, 1758 with >100 species, Atholus Thomson, C.G., 1859 with >80 species and Margarinotus Marseul, 1854 with 10 subgenera and >100 species. Many are associated with dung , decaying vegetation and fungi, mammalian and avian nests, and the colonies of social insects. The species of some genera e.g. Hololepta Paykull, 1811, are saproxylic. They are mostly heavily sclerotized species; diverse in form ranging from oval and convex (typical of Histerini Gyllenhal, 1808, with 26 genera, all >4mm), elongate cylindrical (typical of Exosternini Bickhardt, 1914, a very speciose group) to very flattened and adapted to a saproxylic lifestyle (typical of Hololeptini Hope, 1840 with 6 genera). Fairly consistent characters seem to be the well developed prosternal lobe which is dilated and covers the antennal cavities when the beetle is rolled up, and the lack of labral setae. Most species are basically black, glabrous and shiny but a red or orange pattern to the elytra is not uncommon. The tibiae are usually well developed and, in most species, dentate on the external side, in many dung and compost inhabiting species the fore tibiae are fossorial.
ONTHOPHILINAE MacLeay, 1819
This is a small subfamily containing 7 genera of very distinctive beetles. The mostly Holarctic genus Onthophilus Leach, 1817 is by far the largest with about 40 described species. Most of the other members of the subfamily occur in the Old World tropics although Epiechinus fulvosetosus (Sahlberg, 1913), unusually for the group, occurs throughout Africa, Asia, the Oriental region and south to Australia. Ecologically the group is very varied; many occur in decaying vegetation and dung or among fungi while some occur in mammal or avian nests; sometimes being associated with a single species. The 3 species of Peploglyptus Leconte, 1880 possess pronotal and prosternal trichomes and are probably myrmecophilous, 2 species occur in North and South America and 1 in Borneo. Members of the subfamily are mostly broad and somewhat parallel-sided, flattened dorsally and ventrally, and possess distinct and often exaggerated sculpture to the pronotum and elytra. In some species the elytral sculpture is complex and serves to make the beetle cryptic and difficult to follow when moving, many species move rapidly. The colouration is generally drab although some are metallic.