Insects of Britain and Ireland: the families of Coleoptera

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L. Watson and M. J. Dallwitz

Pselaphidae

Clavigeridae, Staphylinidae-Pselaphinae.

General appearance. 1–3 mm long. Body length/maximum body width 1.5–10. Elytral length/pronotal length 0.9–2. Base of prothorax not or scarcely narrower than the combined elytral bases, or distinctly narrower than the combined elytral bases. Greatest prothoracic width not narrower or only slightly narrower than the greatest elytral width, or distinctly narrower than greatest elytral width. Beetles oval to elongate; conspicuously necked; somewhat waisted to conspicuously waisted; reddish or yellowish. Upper surfaces of body glabrous or subglabrous, or non-glabrous; not bristly; exhibiting scales or scale-like setae, or with neither scales nor scale-like setae.

Detailed morphology. Inclination of the head slight to strong. Eyes strongly protuberant, or not strongly protuberant; bristly, or without bristles; coarsely facetted. Ocelli present; paired. The labrum at least partly visible in antero-dorsal view, or concealed beneath the clypeus; labrum where recorded, mostly moderately to heavily sclerotized. Mandibles with a reduced mola, or without a mola; with reduced prosthecae, or without prosthecae. The mandibular apices simple. The incisor edges of the mandibles simple, or with a single tooth, or with two or more teeth. The maxillae with distinct galea and lacinia apically to the palp, or with a single apical structure additional to the palp. The apical segment of the maxillary palps variously cylindrical to fusiform, or somewhat expanded and truncate to subtriangular, or securiform to cultriform, or aciculate (or uniquely, oddly shaped: enlarged in Pselaphinae, much reduced in Clavigerinae). The apical segment of the labial palps not expanded apically. Antennae very short to long, but not exceeding the insect’s head to tail length; thick, (3–)5 segmented (commonly), or 6–10 segmented, or 11 segmented; without a much-elongated scape; clubbed. Antennal clubs 3 segmented. Antennal insertions visible from above, or hidden from above; ‘countersunk’ within saucer-like fossae, or not in fossae.

Cervical sclerites present, or absent. Prothorax about as long as wide. Pronotal length/maximum pronotal width 0.85–1.3. The pronotum with lateral keels (pronotal carinae), or without lateral keels; keels if present, incomplete. Prothorax at its widest markedly narrower than the adjoining part of the abdomen to not markedly narrower than the adjoining part of the abdomen. Prothorax without notopleural sutures. Scutellum conspicuous to highly reduced, or absent; when applicable, elevated above the mesoscutum in lateral view, or not elevated; anteriorly simple; posteriorly narrowly rounded or acute, or broadly rounded or obtusely angulate. The prosternal process present, or absent; when present, incomplete; falling short of the mesoventrite. Metaventrite without a transverse groove. The fore-leg coxae countersunk in ‘procoxal cavities’. The fore-leg coxal cavities open behind externally; broadly open; medianly confluent; circular to longer than wide; without lateral extensions; internally open. The mid-leg coxae countersunk in ‘mesocoxal cavities’; separated by less than the shortest diameter of the cavity, or more than the shortest diameter of the cavity. The mid-leg coxal cavities contiguous, or narrowly separated, or moderately to widely separated; not or scarcely oblique; open laterally, or closed laterally. Hind-leg coxae contiguous or narrowly separated, or widely separated; not much enlarged; extending laterally to meet the elytra. Tarsal segmentation formula 3, 3, 3, or 0–2, 3, 3. The tarsi with a tiny basal segment that is hard to detect, or without ‘hidden’ segments. The front tarsi present and well developed, or reduced or absent; front tarsi when present, with as many segments as the mid-tarsi, or with one segment fewer than the mid-tarsi; front tarsi 3-segmented (or fewer). Mid-leg tarsi 3-segmented; trimerous; the penultimate segment not distinctly shorter than the antepenultimate one. The claws of the mid-leg tarsi not appendaged. The claws of the mid-leg tarsi simple; without an associated empodium. Hind tarsi with as many segments as the mid-tarsi; 3-segmented.

Elytral length/maximum width across the elytra 0.6–1.1. Elytra meeting along the length of the mid-line; short, exposing several terminal abdominal tergites (leaving most of the abdomen exposed, cf. Staphylinidae); exposing at least one but fewer than three complete abdominal tergites to at least three complete abdominal tergites; truncate. Elytra apunctate, irregularly punctate, or each with fewer than 6 longitudinal lines of punctures or impressed striae. Scutellary striole absent. Wings well developed, or absent or much reduced. Wings without an anal lobe. Wings without a medial fleck. Abdominal sternites 5, or 6; all articulated and moveable. Abdominal segment 8 with apparently functional spiracles, or apparently without functional spiracles. The male external genitalia staphylinoid.

Adult habitat, ecology. Predacious (especially on Springtails); in decaying plant material, in rotting wood, under bark, on shed fur or feathers, and under stones (with the Clavigerinae specialized for life in ants’ nests).

Larvae. Mature larvae minute (less than 3 mm long). The larvae elongate and more or less parallel-sided. Body somewhat flattened. Vestiture restricted to fine hairs or setae, or not restricted to fine hairs or setae. The larvae dorsally only very lightly pigmented or sclerotized; ventrally only very lightly pigmented. The antennae 2 segmented, or 3 segmented. Stemmata present, or absent; on either side of the larval head when present, 1–3. The frontoclypeal suture between frons and clypeus indistinct or absent. The labrum and head capsule completely fused, with no suture apparent. Apices of the mandibles with a single lobe or tooth. The maxillary palps 3 segmented. The labium without ligula between the palps. Labial palps present and segmented; 2 segmented. Mesothoracic legs present and segmented; 5 segmented; with 1 moveable claw. Visible abdominal segments 10. Tergum 9 of the abdomen entirely dorsal. The abdomen having functional spiracles on anterior segments (these annular); without spiracular tubes. The abdominal apex without a respiratory chamber. Abdominal tergum 8 without amature. The last abdominal segment with cerci, or without cerci.

Larvae predacious; in decaying plant material, in rotting wood, under bark, in shed fur or feathers, and under stones (and in ants' nests).

Classification. Suborder Polyphaga; Infraorder Staphyliniformia; Superfamily Staphilinoidea.

Representation in Britain and Ireland, and worldwide. About 9000–10000 species worldwide (especially diverse in the tropics). 51 species in Britain; genera in Britain 19; Batrisodes, Bibloporus, Bibloplectus, Brachygluta, Bryaxis, Claviger, Bythinus, Euplectus, Pselaphaulax, Rybaxis, Trichonyx, Tychus, etc. E.g., Bryaxis puncticollis (Punctured-necked Pselaphus); Trichonyx sulcicollis (Carlisle Pselaphus).

General comments. Adults distinguished from all except Staphylinidae s. stricto by the much abbreviated elytra, and readily distinguished from them by the dorsoventrally inflexible abdomen, and often in having both the antennae and the palps clubbed..

Illustrations. • Bryaxis puncticollis (Punctured-necked Pselaphus: B. Ent. 422). • Bryaxis puncticollis (details, B. Ent. 422). • Bryaxis puncticollis: B. Ent. 422, legend+text. • Bryaxis puncticollis: B. Ent. 422, text cont.. • Trichonyx sulcicollis (Carlisle Pselaphus: B. Ent. 315). • Trichonyx sulcicollis: B. Ent. 315, legend+text. • Trichonyx sulcicollis: B. Ent. 315, text cont.. • Brachygluta, Bryaxis, Bythinus, Pselaphaulax, Reichenbachia, Rybaxis, Trissemus, Trychobythinus: Fowler 3, 77 (1889). • Fowler 3, 77 (1889): original legend.. • Batrisodes, Bibloplectus, Bibloporus, Euplectus, Trichonyx, Trimium (with Ptiliidae): Fowler 3, 78 (1889). • Fowler 3, 78 (1889): original legend.. • Claviger testaceus and Pselaphus heisei, with Scydmaenidae: Fowler 3, 76 (1889). • Fowler 3, 76 (1889): original legend.. • Amauronyx maerkeli, Claviger, Euplectus (2 spp.), Plectophloeus (with Triplax, Coccinellidae and Phalacridae): Fowler Suppl. 12, 1913. • Fowler Suppl. 12, 1913: original legend..


To view the illustrations with detailed captions, go to the interactive key. This also offers full and partial descriptions, diagnostic descriptions, differences and similarities between taxa, lists of taxa exhibiting or lacking specified attributes, and distributions of character states within any set of taxa.

Cite this publication as: ‘Watson, L., and Dallwitz, M.J. 2003 onwards. Insects of Britain and Ireland: the families of Coleoptera. Version: 16th May 2016. delta-intkey.com’.

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