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.
Common name: Rove beetles, staphs
Number of species: 1130
Size Range: 1-24mm
Tarsi: 3-3-3, 5-5-5. Lobed or not.
Description:
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.
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.
The rove beetles are a family (Staphylinidae) of beetles, primarily distinguished by their short elytra (wing covers) that typically leave more than half of their abdominal segments exposed. With over 66,000 species in thousands of genera, the group is the largest family in the beetle order, and one of the largest families of organisms. It is an ancient group, with fossilized rove beetles known from the Triassic, 200 million years ago, and possibly even earlier if the genus Leehermania proves to be a member of this family. They are an ecologically and morphologically diverse group of beetles, and commonly encountered in terrestrial ecosystems.
One well-known species is the devil’s coach-horse beetle (Ocypus olens). For some other species, see list of British rove beetles.
Anatomy
As might be expected for such a large family, considerable variation exists among the species. Sizes range from <1 to 35 mm (1.4 in), with most in the 2–8 mm range, and the form is generally elongated, with some rove beetles being ovoid in shape. Colors range from yellow and red to reddish-brown to brown to black to iridescent blue and green. The antennae usually have 11 segments and are filiform, with moderate clubbing in some genera. The abdomen may be very long and flexible, and some rove beetles superficially resemble earwigs.These beetles are able to fold themselves into a sort of origami shape. In the genera Paederinae, Euaesthetinae, and Osoriinae, and partially in Steninae, the tergum and sternum on the visible abdominal segments have fused, making each segment ring-shaped.
Some rove beetles, including members of Antimerus and Phanolinus,are metallic in appearance.
Some members of Paederina (specifically the genus Paederus), a subtribe of Paederinae, contain a potent vesicant in their haemolymph that can produce a skin irritation called dermatitis linearis,also known as Paederus dermatitis. The irritant pederin is highly toxic, more potent than cobra venom.
Description of rove beetles
Rove beetles are very common insects that usually go unnoticed. They are slender, elongate beetles with the distinctive characteristic of having wing covers (elytra) that are much shorter than the abdomen. The result is that over half of the top surface of the abdomen is exposed. Most rove beetles are black or brown. One common species has grayish markings on the wings and abdomen.
Most rove beetles are medium sized beetles though a few species are up to 1 inch long. Rove beetles are very active fliers or runners. When they run they often raise the tip of the abdomen.
Damage caused by rove beetle
Rove beetles are completely harmless though their habits make them unappealing. They are found in or near decaying organic matter, especially dead animals. They have the interesting (though unpleasant) habit of feeding on other insects such as fly maggots that infest carrion (less often dung or fungus).
Management of rove beetles
There is no special control for these predatory insects. They are not harmful to the house, contents or occupants. The only necessary control is to try to locate a dead animal or other decaying organic matter that is attracting them to the area and remove it. No insecticide sprays are necessary. When the dead animal is removed (or dries completely) these beetles will disappear on their own.
Ecology
Rove beetles are known from every type of habitat in which beetles occur, and their diets include just about everything except the living tissues of higher plants, but now including higher plants with the discovery of the diet of Himalusa thailandensis. Most rove beetles are predators of insects and other invertebrates, living in forest leaf litter and similar decaying plant matter. They are also commonly found under stones, and around freshwater margins. Almost 400 species are known to live on ocean shores that are submerged at high tide, including the pictured rove beetle,although these are much fewer than 1% of the worldwide total of Staphylinidae. Other species have adapted to live as inquilines in ant and termite colonies, and some live in mutualistic relationships with mammals whereby they eat fleas and other parasites, benefiting the host. A few species, notably those of the genus Aleochara, are scavengers and carrion feeders, or are parasitoids of other insects, particularly of certain fly pupae. To profit from the alleged advantages, several Staphylinidae have been transferred into Italy, Hawaii, the continental United States and Easter Island by practitioners. Another advantage of rove beetles is their sensitivity to changes in the environment, such as habitat alteration. This means they have potential as an ecological disturbance indicator in human-dominated environments.
Although rove beetles’ appetites for other insects would seem to make them obvious candidates for biological control of pests, and empirically they are believed to be important controls in the wild, experiments using them have not been notably successful. Greater success is seen with those species that are parasitoids (genus Aleochara).
Rove beetles of the genus Stenus are very interesting insects. They are specialist predators of small invertebrates such as springtails (Collembola). Their labium can shoot out from the head using blood pressure. The thin rod of the labium ends in a pad of bristly hairs and hooks and between these hairs are small pores that exude an adhesive glue-like substance, which sticks to prey.
Systematics
Classification of the 63,650 (as of 2018) staphylinid species is ongoing and controversial, with some workers proposing an organization of as many as 10 separate families, but the current favored system is one of 32 subfamilies, about 167 tribes (some grouped into supertribes), and about 3,200 genera. About 400 new species are being described each year, and some estimates suggest three-quarters of tropical species are as yet undescribed.
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.
Habitat and Food
Habitat: Staphylinidae occupy almost all moist environments throughout the world. Because none of them is truly aquatic, they do not live in open waters; although winged adults may be skimmed from the sea surface far from land, their presence is due to misadventure but attests to their dispersive ability. They live in leaf litter of woodland and forest floors and grasslands. They concentrate in fallen decomposing fruits, the space under loose bark of fallen, decaying trees, drifted plant materials on banks of rivers and lakes, and dung, carrion, and nests of vertebrate animals. Several hundred species live only on seashores. Many are specialized to existence in nests of social insects. Many inhabit caves, underground burrows of vertebrate animals, and smaller soil cavities, even of burrows that they (a few of them) excavate. Many live in mushrooms. Adults and even larvae of a few are associated with living flowers. Others climb on plants, especially at night, and hunt for prey. A few seem to live with terrestrial snails. Their distribution in arid environments is restricted to moist microhabitats.
Food: A little about the feeding habits of Staphylinidae has been deduced from casual observations by many observers, from dissections of alimentary canals, and from feeding trials and examination of mouthparts by a few. Archetypal staphylinids probably were saprophagous (scavengers). Saprophagy is still a major feeding mode in Piestinae, Osoriinae, and Proteininae, perhaps with some adaptation to mycophagy (fungi feeding). Mycophagy has evolved in Oxyporinae, Scaphidiinae, some Tachyporinae, and a few Aleocharinae. Phytophagy (plant feeding) has evolved in some Oxytelinae to the point where the diet of adults and larvae of Bledius consists of diatoms, and at least one species of Apocellus has been accused of damaging flowers, one species of Carpelimus has (probably wrongly) been accused of damaging cucumbers, and one species of Osorius (Osoriinae) has been accused of damaging turf grass. One genus (Himalusa) of the very large subfamily Aleocharinae has been shown to be phytophagous, in that adults of the one species investigated feed on upper leaf surfaces, and larvae feed within leaf petioles of Paederia pilifera Hook. f., a foul-smelling vine in Thailand. Further, one species of Bledius has been blamed for its tunneling, by which it damaged earthen banks around irrigated crops.
Some Omaliinae have evolved toward eating floral parts of plants and others toward carnivory. Saprophagy has evolved toward carnivory in other subfamilies (many Tachyporinae, most Aleocharinae, Pselaphinae, Euaesthetinae, Steninae, Paederinae, and Staphylininae), representing the bulk of species in the family, so that it may be said most Staphylinidae — tens of thousands of species — are facultative predators. Some have specialized, for example: Scydmaeninae and Oligota (Aleocharinae) as predators of mites, Erichsonius (Staphylininae) as predators of soil-inhabiting nematodes, Odontolinus and some Belonuchus and Platydracus (Staphylininae) as predators on mosquito larvae and/or pupae in water-filled flower bracts of Heliconia (Heliconiaceae), at least one Hesperus (Staphylininae) as predator of mosquito larvae in bamboo internodes, and Eulissus (Staphylininae) on adult dung-inhabiting scarab beetles. Aleochara (Aleocharinae) has evolved to become parasitoidal in fly puparia.
Other: The importance of staphylinid predation on pests has been demonstrated repeatedly in the literature. They suppress populations of pest insects and mites in numerous crops (agricultural, horticultural, and forest entomology), and of biting flies (including mosquitoes) and fleas (medical and veterinary entomology). Their presence in carrion gives them a role in forensic entomology. With one exception (Paederus and its close allies), they have trivial importance as pests; but although contact with Paederus may cause dermatitis on human skin, the toxin pederin may be harnessed for its therapeutic effects, and some Paederus species are valuable predators of crop pests. Finally, Staphylinidae form a substantial part of the world’s biodiversity.
