Insects of Britain and Ireland: the families of Coleoptera

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L. Watson and M. J. Dallwitz


= Trichopterygidae; including Cephaloplectidae, Limulodidae.

Feather-winged beetles.

General appearance. 0.4–1.1 mm long. Body length/maximum body width 1.5–5.6. Elytral length/pronotal length 0.85–3.1. Base of prothorax not or scarcely narrower than the combined elytral bases. Greatest prothoracic width not narrower or only slightly narrower than the greatest elytral width. Body not noticeably widest either behind the thorax, or at the rear. Beetles oval to elongate; dorsally flattened, or dorsally somewhat convex; not necked; somewhat waisted to conspicuously waisted; neither particularly long- nor short-legged to decidedly short-legged; black, reddish, yellowish, pitchy, etc., and various combinations. Upper surfaces of body glabrous or subglabrous, or non-glabrous; not bristly; with neither scales nor scale-like setae.

Detailed morphology. Eyes strongly protuberant, or not strongly protuberant; without bristles; coarsely facetted. The labrum at least partly visible in antero-dorsal view; labrum mostly moderately to heavily sclerotized. Mandibles with a well developed mola, or with a reduced mola. The mandibular apices simple. The incisor edges of the mandibles simple. The maxillae with distinct galea and lacinia apically to the palp. The apical segment of the maxillary palps aciculate. The apical segment of the labial palps not expanded apically. Antennae short to long, but not exceeding the insect’s head to tail length; (8–)11 segmented; hairy (each segment with a whorl of long setae); clubbed. Antennal clubs loosely 3 segmented. Antennal insertions visible from above, or hidden from above; not hidden by lateral extensions of the frons.

Cervical sclerites absent. Prothorax shorter than wide. Pronotal length/maximum pronotal width 0.5–1.6. The pronotum with lateral keels (pronotal carinae); keels complete. Prothorax at its widest not markedly narrower than the adjoining part of the abdomen; with neither produced front corners nor serrated sides. Prothorax without notopleural sutures. Scutellum conspicuous; not elevated; anteriorly simple; posteriorly narrowly rounded or acute, or broadly rounded or obtusely angulate. The prosternal process present, or absent; when present, complete, or incomplete; when applicable, falling short of the mesoventrite, or slightly overlapping 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 to narrowly open; medianly confluent, or narrowly separated; circular to longer than wide; with narrow lateral extensions, or without lateral extensions; internally open, or internally closed by a slender bar, or broadly closed internally. 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; much enlarged; extending laterally to meet the elytra, or not markedly extended laterally; posteriorly shaped to receive the retracted femur; produced behind into flat plates which conceal the hind femora when these are retracted. Tarsal segmentation formula 3, 3, 3, or 0–2, 3, 3. The tarsi without bilobed segments; 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 at most 3-segmented. 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. Hind tarsi with as many segments as the mid-tarsi; 3-segmented.

Elytral length/maximum width across the elytra 0.55–3.5. Elytra meeting along the length of the mid-line; covering most to all of the abdomen to short, exposing several terminal abdominal tergites; exposing no more than part of the terminal tergite to at least three complete abdominal tergites; truncate (Acrotrichinae), or not truncate (Ptiliinae). Elytra with six or more longitudinal lines of punctures, or 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; when present, without veins; fringed with long hairs on the hind margin (characteristic in form, being very narrow and fringed with long setae). Wings without an anal lobe. Wings without a medial fleck. Abdominal sternites 6–7; all articulated and moveable. Abdominal segment 8 with apparently functional spiracles, or apparently without functional spiracles. The male external genitalia staphylinoid.

Adult habitat, ecology. Land-dwellers; in decaying plant material, in rotting wood, under bark, and associated with dung, or on shed fur or feathers (or in ants'nests); consuming decaying plant material and mycetophagous (mainly on moulds).

Larvae. Mature larvae minute (less than 3 mm long). The larvae elongate and more or less parallel-sided. Body circular in cross-section. Vestiture restricted to fine hairs or setae. The larvae dorsally only very lightly pigmented or sclerotized; ventrally only very lightly pigmented. The antennae 3 segmented. Stemmata absent. The frontoclypeal suture between frons and clypeus indistinct or absent. The labrum and head capsule separated by a complete suture. Apices of the mandibles with a single lobe or tooth, or bilobed or bidentate. The maxillary palps 3 segmented. The labium with a short ligula between the palps, or with a ligula at least as long as 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 in decaying plant material, in rotting wood, under bark, associated with fungi, and in dung, or in carrion, or in shed fur or feathers (or even in ants' nests); mainly(?) mycetophagous (on moulds).

The larvae elongate, with 3-segmented antennae and well-developed thoracic legs.

Classification. Suborder Polyphaga; Infraorder Staphyliniformia; Superfamily Staphilinoidea.

Representation in Britain and Ireland, and worldwide. About 630 species worldwide; genera about 85. 90 species in Britain; genera in Britain 18; Acrotrichis, Actidium, Actinopteryx, Euryptilium, Micridium, Microptilium, Nanoptilium, Nephanes, Nossidium, Oligella, Plitium, Ptenidium, Pteryx, Ptiliolum, Ptilium, Ptinella, Raeocrara, Smicrus.

General comments. Hind coxae with deep cavities into which the femora can be retracted; the hindwings narrow and feather-like. This family includes the smallest known Coleoptera..

Illustrations. • Acrotrichis (5 spp.), Actinopteryx, Nanoptilium, Ptiliolum (2 spp.), Ptilium: Fowler 3, 79 (1889). • Fowler 3, 79 (1889): original legend.. • Ptinella (3 spp.) and Pteryx suturalis (with Pselaphidae): Fowler 3, 78 (1889). • Fowler 3, 78 (1889): original legend.. • Acrotrichis, Actidium, Euryptilium, Nossidium, Ptenidium, Ptilium (with Corylophidae and Spaeriidae): Fowler 3, 80 (1889). • Fowler 3, 80 (1889): original legend.. • Ptenidium pusillum: Rye & Fowler XVI2).

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.’.