Insects of Britain and Ireland: the families of Coleoptera
General appearance. 0.8–1.8 mm long. Body length/maximum body width 1.1–1.55. Elytral length/pronotal length 0.85–3.6. 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. Beetles broadly oval; dorsally somewhat convex to dorsally strongly convex; not necked; not waisted. Upper surfaces of body glabrous or subglabrous, or non-glabrous; not bristly; with neither scales nor scale-like setae. Beetles rolling into a ball when alarmed (sometimes), or not conglobulating.
Detailed morphology. Inclination of the head slight. 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. The mandibular apices simple, or bidentate or bilobed (some Clambinae). The incisor edges of the mandibles with two or more teeth. 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 not expanded apically. Antennae short; 8–10 segmented; clubbed. Antennal clubs 2 segmented. Antennal insertions visible from above, or hidden from above.
Cervical sclerites present. Pronotal length/maximum pronotal width 0.3–0.5. The pronotum with lateral keels (pronotal carinae); keels complete. Prothorax without notopleural sutures. Scutellum conspicuous to highly reduced, or absent (some Clambinae); when applicable, elevated above the mesoscutum in lateral view; anteriorly simple; posteriorly narrowly rounded or acute. The prosternal process present (Calyptomerinae), or absent (Clambinae); when present, incomplete; when present, 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; strongly transverse, or slightly transverse; without lateral extensions; internally open (Clambinae), or internally closed by a slender bar (Calyptomerinae), or broadly closed internally (Acalyptomerinae). The mid-leg coxae countersunk in mesocoxal cavities; separated by less than the shortest diameter of the cavity. The mid-leg coxal cavities contiguous, or narrowly separated (Acalyptomerinae); not or scarcely oblique, or markedly oblique (some Calyptomerinae); open laterally. Hind-leg coxae contiguous or narrowly separated (Calyptomerinae), or widely separated (Acalyptomerinae); much enlarged, or not much enlarged; extending laterally to meet the elytra; posteriorly shaped to receive the retracted femur (transversely excavated). Tarsal segmentation formula 5, 5, 5. The tarsi without bilobed segments; without hidden segments. Front tarsi with as many segments as the mid-tarsi; 4-segmented. Mid-leg tarsi 4-segmented (usually, cf. Imms (1957), Britton 1970, Lawrence et al. 1999); tetramerous (sometimes trimerous in non-British species); 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; 4-segmented.
Elytral length/maximum width across the elytra 0.85–1.2. Elytra exposing no more than part of the terminal tergite; non-glabrous (sparsely setose). Elytra with six or more longitudinal lines of punctures (some Acalytomerinae), 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, 12 or more. Scutellary striole absent. Wings well developed; fringed with long hairs on the hind margin, or not fringed. Wings with an anal lobe, or without an anal lobe. Wings without a medial fleck. Abdominal sternites 5–6; all articulated and moveable. Abdominal segment 8 with apparently functional spiracles, or apparently without functional spiracles. The male external genitalia trilobate.
Adult habitat, ecology. Not predacious (?); in decaying plant material.
Larvae. Mature larvae minute (less than 3 mm long). The larvae elongate and more or less parallel-sided. Body circular in cross-section, or somewhat flattened. 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 present; on either side of the larval head 1, or 3, or 5, or 6. The frontoclypeal suture between frons and clypeus indistinct or absent, or distinct. The labrum and head capsule separated by a complete suture. Apices of the mandibles bilobed or bidentate, or trilobed or tridentate. The maxillary palps 2 segmented, or 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; 1 segmented, or 2 segmented. Mesothoracic legs present and segmented; 5 segmented; with 1 moveable claw. Visible abdominal segments 10. Tergum 9 of the abdomen extending to the underside. The abdomen having functional spiracles on anterior segments (these annular); with anterior and 8th-segmental spiracles borne at the ends of a series of spiracular tubes. The abdominal apex without a respiratory chamber. Abdominal tergum 8 without amature. The last abdominal segment without cerci.
Larvae not predacious (?); in decaying plant material and in dried plant material; mycetophagous (eating moulds and spores).
Classification. Suborder Polyphaga; Infraorder Elateriformia; Superfamily Eucinetoidea.
Representation in Britain and Ireland, and worldwide. About 50 species worldwide; genera 5. 9 species in Britain; genera in Britain 2; Calyptomerus, Clambus.
General comments. Very small, oval beetles, commonly conglobulating when alarmed. Unwin gives tarsi as 5,5,5, seemingly in error: the other sources give 4,4,4, with Lawrence et al. also allowing 3,3,3.
Illustrations. • Calyptomerus, Clambus (from Joy). • Calyptomerus dubius and Clambus pubescens (with Leptinidae and Leiodidae): Fowler 3, 71 (1889). • Fowler 3, 71 (1889): original legend.. • Clambus punctulus: Fowler 6, 13 (1913).
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’.