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A large family, containing more than a quarter of the British beetle species, 1122 in total on the 2012 British list. As can be expected from such a diverse group, there is considerable variety: species vary in size between 0.7 and 28mm and in shape from fusiform (almost tadpole-shaped) to very elongate and segmented. The group is characterised by short elytra, covering less than half the abdomen, and most species are similar in form to the largest and most familiar species, the Devil’s coach-horse Ocypus olens (Muller). The family is divided into 18 subfamilies, including several which have previously been raised to family level.
Omaliinae contains 71 British species, mostly brown or black beetles shorter and broader in shape than the stereotypical staphylinid, with proportionally longer wing cases. Although some species (notably Phyllodrepa nigra (Gravenhorst) and Dropephylla heeri (Heer)) are known from only a few localities, many are widespread and common in a variety of habitats, including coming to light, and dung or fungi can be particularly productive. The subfamily is distinguished by the presence of a pair of ocelli on the head, level with the hind margin of the eyes.
Proteininae has 11 British representatives, with long elytra and a broad shape similar to the Omaliinae (without the two ocelli characteristic of that subfamily). Common in decaying vegetable matter, rotting fungi and (in the case of Proteinus), in carrion.
There are just five British species of subfamily Micropeplinae: their strongly-ridged abdomen, elytra and pronotum soon become distinctive, though at 1.5-2.5mm specimens are likely to need examination under a microscope to fully appreciate it. Found mainly in warm decaying vegetable matter such as compost heaps.
Subfamily Pselaphinae are a group which is sometimes raised to family level. Containing 52 small (0.7-3.5mm) British species, many of which are rare, the Pselaphinae mainly feed on orobatid mites. Many resemble ants in general appearance, and two species (Claviger longicornis Müller and C. testaceus Preyssler) are myrmecophilous with ants of genus Lasius.
Phloeocharinae is represented by just one species in Europe, Phloeocharis subtilissima Mannerheim. A small (1.5-2mm) cylindrical species with reddish elytra and appendages, it is covered with long pale pubescence making it relatively easy to distinguish from similar species such as the Tachyporinae (Staphylinidae). It is widespread in moss or beneath bark on trees.
Subfamily Tachyporinae contains 66 2-8mm species, including some of the most distinctive staphylinids (Tachyporus spp.). All are fusiform in shape and most are shining black or brown in colour, many with bright orange sections. Common and often abundant in decaying vegetation and fungi, but also frequent in most other habitats.
Trichophyinae has just one European species, the 2.5-3mm Trichophya pilicornis (Gyllenhal). Widespread but local, it can be found in decaying vegetation and moss and is particularly associated with wood chippings and sawdust in woodland. The unusual antennal structure (two dilated basal segments with the outer segments thin and threadlike) distinguish this subfamily from all others except Habrocerinae, and it can be split from the latter on pronotal form (T. pilicornis widest across the middle, Habrocerinae widest at the hind margin).
There is one British member of subfamily Habrocerinae: Habrocerus capillaricornis (Gravenhorst). Similar in appearance to Trichophyinae, with the same unusual antennae, this species is slightly larger (3-3.5mm). Found mainly in leaf litter and other decaying vegetation.
The subfamily of many coleopterist’s nightmares, the Aleocharinae contains 454 often very similar species. The group as a whole is characterised by having the antennae inserted on top of the head around the level of the eyes, rather than on the front or side. Frequently common whatever habitat is examined, the learning curve is long and steep. Decaying vegetation, dung, carrion and rotten fungi will produce large numbers of Aleocharines, and most areas or habitats will have characteristic species. Dissection and a reliably-identified reference collection are frequently the minimum required for progress with this group.
Subfamily Scaphidiinae (family Scaphidiidae in older texts) has only five British species. All are shining black beetles between 2 and 6mm long, the commonest of which is Scaphidium quadrimaculatum Olivier, pointed-oval in shape with four red spots (two on each elytron) on a shining black background. Two species (Scaphium immaculatum (Olivier) and Scaphisoma assimile Erichson) have not been found in Britain since 1936 and 1974 respectively and may well be extinct in the country.
Piestinae contains a single British species, Siagonium quadricorne Kirby. This is a flat, 5mm long, parallel-sided beetle with dark red elytra and appendages, found under bark. The male has highly-distinctive horns outside of the mandibles where the head is produced forwards outside the prominent mandibles.
Subfamily Oxytelinae has 94 shining black, brown or red British members, 2-9mm long. Broadly similar to the Omaliinae, this group also have the antennae inserted beneath the sides or front of the head but do not possess the ocelli that characterise the smaller group. Mostly found near water or in marshy places, they come to light and can be caught in moth traps. The 27 species of Bledius are interesting: their fossorial legs provide a clue as to their habit of digging shallow galleries through the clay or sand of waterside areas, where they can be detected by the spoil heaps they leave behind.
Oxyporinae contains a single species, Oxyporus rufus (L.). This species is 11mm long with orange legs, large black mandibles, and bands of black and bright orange across the body lending it a distinctive appearance. Can be found relatively frequently in the gills of fungi.
Formerly a family in their own right, the Scydmaeninae (ant-like stone beetles) are similar in appearance to the Pselaphinae but have longer elytra. The subfamily contains 32 small (0.7-2.2mm) species, most of which bear a passing resemblance to ants. Most live in damp habitats, particularly leaf litter, rotten wood and other decaying organic matter.
Subfamily Steninae contains 75 species in Britain, most of which occur near water. 74 of the Steninae are species of the genus Stenus, and the bug-eyed, elongate appearance quickly becomes distinctive. The remaining species, Dianous coerulescens (Gyllenhal), is similar to Stenus but has smaller eyes, a blue or green sheen (Stenus are black) and an orange spot on each elytron. It can be found in wet moss by waterfalls or fast-flowing streams.
There are four members of Euaesthetinae on the 2012 British list. All are small (1-2mm), with a broad two-segmented antennal club borne on short antennae, barely longer than the clubbed maxillary palps. The species can be found in a range of habitats, including grass tussocks, marshland vegetation (particularly the roots of rushes) and flood debris, and are widespread but local.
Pseudopsinae contains a single British species, Pseudopsis sulcata Newman. Measuring 3-4mm in length, the pronotum and elytra have distinctive ridges, similar in appearance to the Micropeplinae but with unclubbed antennae. Found mainly in decaying vegetable matter, particularly underneath hay or straw mixed with dung, the species is local but widespread.
The Paederinae has 62 2-10mm British members, many of which are distinctively coloured with black and orange banding. The distinguishing character for the group is a small terminal segment of the maxillary palp, on an apically-widened penultimate segment. Widespread in most habitats, Paederinae are found particularly frequently in decaying organic matter, particularly in marshland or other riparian habitats. Some species of genus Paederus contain toxins in the haemolymph which can cause dermatitis if the beetle is squashed against the skin.
Subfamily Staphylininae contains 185 species, including the largest Staphylinids found in Britain. Some are particularly unusual, including Emus hirtus (L.), a dung-feeding bee mimic now restricted to Kent, Velleius dilatatus (Fabricius), found in hornet (Vespa crabro L.) nests, and Remus sericeus Holme, a specialist of decaying seaweed.
The antennal insertion placement (on the front of the head between the bases of the large mandibles, forward of the eyes) serves to identify the subfamily, although Aleocharinae has some confusion species. Decaying organic matter, particularly dung, carrion, rotten fungi, and compost heaps can be very productive, but the aggressive nature of these beetles means far more specimens may be captured than survive all the way home if potted together.
