Quedius Stephens, 1829

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POLYPHAGA Emery, 1886

STAPHYLINOIDEA Latreille, 1802

STAPHYLINIDAE Latreille, 1802

STAPHYLININAE Latreille, 1802

STAPHYLININI Latreille, 1802

Among the larger of the staphylinid genera, this genus includes more than 800 species in up to twelve subgenera, although this total is likely to be greatly increased as the faunas of Russia and China are investigated. While the group is more or less cosmopolitan the greatest diversity by far is in the Palaearctic region; about 100 species of seven subgenera are known from North America while about 90 are known from Russia and the European fauna includes more than 200 species and subspecies. Obviously this reflects the research applied to the European fauna and it also suggests that other Palaearctic faunas are likely to be only poorly known. Our UK fauna includes 45 species in 5 subgenera. At present the subgeneric classification should not be taken too seriously; the well-known genus Velleius Leach, 1819, with 8 Palaearctic species of which only one occurs in Europe including the UK, is now included as a subgenus of Quedius, and several exotic subgenera such as Velleiopsis Fairmaire, 1882 from the south-western Pacific, and the Nearctic Megaquedius Casey, 1915 are now synonymised with Microsaurus Dejean, 1833. Several species of Microsaurus have recently been transferred to Distichalius Casey, 1915, several Distichalius to Raphirus Stephens, 1829, and several Microsaurus to Raphirus. To further emphasize this at least 6 genera, known from only from a few specimens, are now removed from Quediini and included in Staphylininae incertae sedis. With the exception of Velleius all the Palaearctic subgenera are represented in the Nearctic region, and many species from other regions e.g. all those from tropical Africa, have been re-assigned to other genera, and so it is likely, ultimately, that the genus will include only a large number of species from the Holarctic region along with a host of adventives in other regions. The genus has never been popular and, outside the Nearctic/Western Palaearctic regions, there are likely to be many species that remain to be discovered and that will re-define the genus, but for now it remains the type genus of the Quediini Kraatz, 1857, a group of about nine genera and at least two subtribes, and a group that is sometimes included among the subtribes of a more widely defined Staphylinini Latrielle, 1802. Despite such nonsense the genus remains well defined among the European fauna and the various subgenera are reasonably distinct, see below.

With a little experience most members of the Quediini have a rather characteristic appearance, the head is usually rather small and rounded, the pronotum rounded and transverse or quadrate, and the abdomen long and parallel-sided or tapering. The majority of species may be recognized by the two longitudinal series of three punctures which are confined to the anterior half of the pronotum, but more generally the subtribe is characterized by the following characters: Head and pronotum, at least laterally, microsculptured. Head with frontoclypeal punctures as well as anterior and basal punctures which are larger than any ground punctation. Pronotum and prosternum completely separate, with a complete border from the anterior angles, pronotum slightly elongate to strongly transverse, shield-shaped and either impunctate or characteristically punctured. Wings with separate CuA and MP4 veins. Abdominal tergites with only basal impressions; never with basal ridges or apical impressions. Front femora without an apical row of lateroventral spines, front tibiae without a subapical notch and all protarsi with a pair of empodial setae. Most species are shiny black or substantially so but many have contrasting red elytra, many have pale or partly pale appendages and/or abdominal segments, in many the abdomen has a metallic lustre and in some the pubescence may form bicoloured patterns on the abdomen although in general it is entirely dark. Quedius may be recognized among our UK fauna by the form of the pronotum (see Q. lateralis (Gravenhorst, 1802); rounded and broadest in the basal half, with discal punctures confined to the apical half and a border than runs along the lateral margin and does not reflex under the anterior angle, coupled with a distinctly microsculptured head, a well-developed apical maxillary palpomere (at least as long and only slightly narrower than the penultimate segment) and dilated basal segments of the front tarsi. The elytra are usually densely punctured but Q. cinctus (Paykull, 1790) is the exception, here they are shiny with scattered micropunctures and two longitudinal series of larger setiferous punctures on each, Quedionuchus plagiatus Mannerheim, 1843, formerly included in Quedius, also has two longitudinal series of punctures on each elytron but here the cuticle is microsculptured and rather densely microsculptured. More generally many species have large convex eyes which may occupy the entire lateral margin, large and robust mandibles and filiform antennae with most segments elongate although Velleius is the exception here. The head is glabrous but for various sensory setae and, in many, a patch of dense setae behind the eyes, the arrangements of which have often been used in keys to species but they are known to vary within species. The labrum bears long forwardly-pointing setae and has either an entire or a notched anterior margin. The apical margin of the elytra and some distal abdominal tergites bear a fringe of stiff dark setae which are usually obvious among any finer pubescence. The front tarsi are dilated in both sexes but usually more so in males. Some of these characters make the subgenera easy to recognize, at least among our UK fauna:

Antennomeres 4-10 widely expanded internally. Body length >15mm.

-Velleius

Antennomeres 4-10 normal. Body length at most 13mm.

-2

Elytra with 2 rows of 4-5 punctures, one adjacent to the suture and one on the disc, usually with the margins contrastingly paler.

-Distichalius

Elytra evenly and densely punctured, without longitudinal series of larger punctures. Colour variable but not as above.

-3

Eyes smaller, occupying at most slightly more than half the lateral margin and shorter or only a little longer than the temples when viewed from above.

-Microsaurus

Eyes larger, distinctly longer than the temples and occupying at least two-thirds of the lateral margin.

-4

Apical margin of the labrum evenly curved, not expanded or incised. Larger species, 10-13 mm, with more parallel-sided abdomen.

-Quedius

Apical margin of the labrum bilobed or at least distinctly incised at the centre (may need to be looked for carefully among the setae). Mostly smaller species, 4.5-9.0 mm although one, Q. picipes (Mannerheim, 1830), is larger, 8-11 mm, with a distinctly tapering abdomen.

-Raphirus

Identification is straightforward for many species, especially once the subgenus is established, there tend to be many good characters involving size, setae and colour etc., and the morphology of the head, in particular, can provide many good characters, but likewise many specimens will need to be dissected. The aedeagi of most are distinctive although sometimes often only comparatively so and good diagrams will be needed. The aedeagus has a single paramere which is often asymmetric and sometimes has series of darker spots towards the apex, and a median lobe which is often distinctively constricted medially, pointed or rounded apically, and sometimes distinctly twisted or asymmetric. In most cases these structures are comparatively large, well-sclerotized and easily dissected, the features of both the median lobe and the paramere are easily seen at X40 or so, especially if the structure is submerged, but in a few cases they will need to be separated and this requires care, especially as the darker spots towards the apex of the paramere may become dislodged. Being well sclerotized the structures are easily preserved by drying and gluing them to the same card as the specimen.

Among our UK fauna only a few genera have a similar margined form of pronotum but these are easily recognized; in both Acylophorus Nordmann, 1837 and Euryporus Erichson, 1839 the pro-tarsi are not dilated, in Heterothops Stephens, 1829 the apical maxillary palpomere is shorter and narrower than the penultimate segment and tapers to a point, and in Astrapaeus Gravenhorst, 1802 the elytra are glabrous and shiny with two irregular series of punctures, one by the suture and one on the disc, and the terminal labial palpomere is dilated and truncate across the apex.

Species occur in a very wide range of habitats and are often common in humid microhabitats in wooded, open or subterranean ecosystems. So far as is known all species are predatory both as adults and larvae, many are diurnal but it is likely that most are primarily crepuscular and nocturnal, especially among those that hunt in exposed situations such as pathways and tree trunks. Adults and larvae are likely to occur in any habitat hosting large populations of small insects and their larvae such as decaying fungi, compost and dung, they also occur in bird and mammal nests and a few, occur in hymenoptera nests, most notably Velleius which is associated with Hornets (Vespa crabro L.) while most species of Quedius s.str. and larger species of Raphirus occupy more general habitats, often on humid substrates or wetland margins. Some have more specialized lifestyles e.g. adults of Q. brevis Erichson, 1840 occur in Wood Ant (Formica rufa L.) nests during winter and early spring while their larvae have been recorded from nests of the ant Lasius fuliginosus (Latreille, 1798). The vary common Q. lateralis (Gravenhorst, 1802) is a general predator that has on several occasions been recorded from Badger setts. Q. longicornis Kraatz. 1857 is usually recorded from subterranean mammal nests, especially those of moles, but also, occasionally occurs in avian nests in tree hollows. The very local Q. nigrocaeruleus Fauvel, 1874 also occurs in subterranean mammal nests but has also been recorded more widely, from avian nests and also from those of bees and wasps and it is sometimes associated with decaying fungi. More generally there are many species likely to be found among subterranean mammal nests, the most frequent being Q. puncticollis (Thomson, 1867). Several species are associated with debris-filled hollows in decaying trees and are rarely found elsewhere, these include Q. truncicola Fairmaire & Laboulbiene, 1856, Q. scitus (Gravenhorst, 1806) and Q. xanthopus Erichson, 1839 among others. Q. lucidulus Erichson, 1839 is only recently known from the UK, it was sampled from an interception trap in Sussex and so the lifestyle is unknown but on the continent it occurs mostly among litter and decaying fungi in conifer woodlands. Several seem to have very narrow ecological requirements e.g. Q. auricomus Kiesenwetter, 1850 is associated with wet moss and tussocks by energetic streams, waterfalls and rock seepages, while Q. boopoides Munster, 1923 is associated with blanket bogs and wet mires in upland situations. Several e.g. Q. plancus Erichson, 1840 and Q. riparius Kellner, 1843 seem to occur only on wetland margins, and these generally have more limited distributions.

The genus really does afford a good opportunity to study in depth a group of rove beetles. Many are widespread, common and occur in a variety of habitats and there are good keys to our UK species (see the RES handbook). Casual sampling of decaying vegetation, fungi and dung may produce a range of species, several may be found at carrion in just about any situation and many can be found throughout the year. Many of the commoner species occur regularly in parks, gardens and other disturbed habitats, and searching pathways and trunks at night may produce species that are otherwise rarely observed. Digging up old mammal nests and sieving or putting old avian or hymenoptera nests through the extractor are good ways to record unusual species, as is pitfall-trapping. Searching sap runs at night is the best way to find Velleius, and this is probably worthwhile in any situation as the species seems to have expanded greatly in recent years.