Insects of Britain and Ireland: the families of Coleoptera

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L. Watson and M. J. Dallwitz



False Skin Beetles.

General appearance. 2.7–3.5 mm long. Body length/maximum body width 1.5–2.9. Elytral length/pronotal length 2.6–3.2. 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, or distinctly narrower than greatest elytral width. Beetles elongate-oval to elongate; dorsally flattened; not necked; not waisted to somewhat waisted; decidedly short-legged; the elytra of D. lunatus black, with a lunate ptch of white pubescence in the middle. Upper surfaces of body non-glabrous; exhibiting stiff, erect, dark bristles, or not bristly; with neither scales nor scale-like setae.

Detailed morphology. Beetles not prognathous. Inclination of the head slight. Eyes strongly protuberant; bristly; coarsely facetted. The labrum at least partly visible in antero-dorsal view, or concealed beneath the clypeus; labrum if recognizable, mostly moderately to heavily sclerotized. Mandibles with a well developed mola. The mandibular apices bidentate or bilobed. 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 cylindrical to fusiform. The apical segment of the labial palps more or less expanded apically. Antennae short; 11 segmented; without a much-elongated scape. Antennal scape not swollen. Antennae clubbed. Antennal clubs flattened, 2 segmented (cf. Joy), or 3 segmented (cf. Unwin). Antennal insertions hidden from above.

Cervical sclerites present. Prothorax shorter than wide (with conspicuous, complete lateral keels). Pronotal length/maximum pronotal width 0.45–0.72. The pronotum with lateral keels (pronotal carinae); keels complete. Prothorax at its widest not markedly narrower than the adjoining part of the abdomen. Prothorax without notopleural sutures. Scutellum conspicuous; abruptly elevated above the mesoscutum in lateral view; anteriorly simple; posteriorly broadly rounded or obtusely angulate, or truncate. The prosternal process complete; slightly overlapping the mesoventrite. Metaventrite without a transverse groove. The fore-leg coxae countersunk in ‘procoxal cavities’. The fore-leg coxal cavities closed behind externally; broadly closed; quite widely separated; slightly transverse; with narrow lateral extensions, or without lateral extensions; broadly closed internally. The mid-leg coxae countersunk in ‘mesocoxal cavities’; separated by less than the shortest diameter of the cavity. The mid-leg coxal cavities moderately to widely separated; not or scarcely oblique; open laterally. Hind-leg coxae contiguous or narrowly separated; not markedly extended laterally; moveable; not shaped posteriorly to receive the femur. Tarsal segmentation formula 5, 5, 5. The tarsi without bilobed segments (in British species, but the third segment with a membranous lobe beneath); in British species without ‘hidden’ segments. Front tarsi with as many segments as the mid-tarsi; 5-segmented. Mid-leg tarsi 5-segmented; pentamerous; the penultimate segment not distinctly shorter than the antepenultimate one, or 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; 4-segmented, or 5-segmented.

Elytral length/maximum width across the elytra 1.2–2.2. Elytra covering most to all of the abdomen; exposing no more than part of the terminal tergite; non-glabrous; coarsely striate. 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; the lines per elytron when more than five, 10. Scutellary striole present. Elytra with epipleura. Elytral epipleura reaching to the tips of the elytra. Wings well developed. Wings with an anal lobe. Wings with a medial fleck; the medial fleck bisected by a vein. Abdominal sternites 5; all articulated and moveable. Abdominal segment 8 apparently without functional spiracles. The male external genitalia cucujiform.

Adult habitat, ecology. Under bark and associated with fungi (D. lunatus “in black fungi on dead ash trees”: Joy); mycetophagous.

Larvae. Mature larvae minute (less than 3 mm long), or small to medium-sized. The larvae elongate and more or less parallel-sided. Body circular in cross-section. Vestiture restricted to fine hairs or setae. The larvae dorsally heavily pigmented or sclerotized; ventrally only very lightly pigmented. The antennae 3 segmented. Stemmata present; on either side of the larval head 6. The frontoclypeal suture between frons and clypeus indistinct or absent. The labrum and head capsule partly fused, with an incomplete suture. Apices of the mandibles bilobed or bidentate. The maxillary palps 3 segmented. The labium with a short 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-biforous); with the spiracles on the eighth segment borne at the ends of spiracular tubes, or without spiracular tubes. The abdominal apex without a respiratory chamber. Abdominal tergum 8 without amature. The posterior segments without swimming hairs. The last abdominal segment with cerci, or without cerci.

Larvae presumably not predacious; under bark and in rotting wood (especially associated with decaying logs), or associated with fungi (e.g., in ascomycete fruit bodies).

Classification. Suborder Polyphaga; Superfamily Cucujoidea.

Representation in Britain and Ireland, and worldwide. About 195 species worldwide. 2 species in Britain; genera in Britain 2; Biphyllus, Diplocoelus.

General comments. Thorax with a ridge surmounted by a row of bent bristles down each side; scutellum transverse; tarsi sometimes 4 segmented in non-British species; the medial feck of the hindwing partly bisected by a vein.

Illustrations. • Biphyllus (from Joy). • Biphyllus lunatus and Diplocoelus fagi (with Cucujidae, Silvanidae etc.): Fowler 3, 93 (1889). • Fowler 3, 93 (1889): 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.’.