Insects of Britain and Ireland: the families of Coleoptera

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L. Watson and M. J. Dallwitz

Eucnemidae

Melasidae, ~Elateridae.

False Click-beetles.

General appearance. 2.8–30 mm long (?). Body length/maximum body width 2.4–3.6. Elytral length/pronotal length 2.35–4.85. 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 elongate to slender; not necked; not waisted. Upper surfaces of body non-glabrous; not bristly; with neither scales nor scale-like setae. Beetles not clicking and ‘jumping’ (the clicking mechanism apparently non-functional).

Detailed morphology. Inclination of the head slight to very strong. Eyes strongly protuberant, or not strongly protuberant; without bristles; finely facetted. The frons with a transverse ridge between the eyes. The labrum concealed beneath the clypeus; labrum if recordable, mostly moderately to heavily sclerotized, or mostly membranous or only very lightly sclerotized. Mandibles without a mola; without prosthecae. The mandibular apices simple, or bidentate or bilobed. The incisor edges of the mandibles simple, or with a single tooth. 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 cylindrical to fusiform, or somewhat expanded and truncate to subtriangular, or securiform to cultriform. The apical segment of the labial palps not expanded apically. Antennae very short to short; 11 segmented. Antennal scape not swollen. Antennae filiform, or serrate, or pectinate. Antennal insertions visible from above, or hidden from above; ‘countersunk’ within saucer-like fossae, or not in fossae.

Cervical sclerites present. Prothorax shorter than wide. Pronotal length/maximum pronotal width 0.48–1. The pronotum with lateral keels (pronotal carinae); keels complete. Prothorax without notopleural sutures. Scutellum conspicuous; elevated above the mesoscutum in lateral view; anteriorly simple; posteriorly narrowly rounded or acute, or broadly rounded or obtusely angulate, or truncate. The prosternal process complete; moderately or strongly 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, or narrowly open; quite widely separated; circular to longer than wide; without lateral extensions; internally open, or internally closed by a slender bar. 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 moderately to widely separated; not or scarcely oblique; open laterally. Hind-leg coxae contiguous or narrowly separated; extending laterally to meet the elytra; contiguous, posteriorly shaped to receive the retracted femur (with transverse cavities). Tarsal segmentation formula 5, 5, 5. The tarsi without bilobed segments; 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. The claws of the mid-leg tarsi not appendaged (but sometimes with basal setae). The claws of the mid-leg tarsi simple, or one-toothed or bifid, or serrate, denticulate or pectinate; with an empodium between them (this with no more than two setae), or without an associated empodium. Hind tarsi with as many segments as the mid-tarsi; 5-segmented.

Elytral length/maximum width across the elytra 1.7–3. Elytra exposing no more than part of the terminal tergite; hard; non-glabrous. Elytra with six or more impressed striae, 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, 9. Scutellary striole absent. Wings well developed. Wings with an anal lobe, or without an anal lobe. Wings without a medial fleck. Abdominal sternites 5; all fused and immoveable. Basal abdominal sternites immovably joined 5 (sternite 5 not movable on 4). Abdominal segment 8 with apparently functional spiracles. The male external genitalia trilobate.

Adult habitat, ecology. Not predacious (?); often found on living vegetation.

Larvae. Mature larvae minute (less than 3 mm long) to relatively large. The larvae elongate and more or less parallel-sided, or oblong to ovate. Body circular in cross-section, or somewhat flattened, or strongly flattened. Vestiture restricted to fine hairs or setae. The larvae dorsally heavily pigmented or sclerotized, or dorsally only very lightly pigmented or sclerotized; ventrally more or less heavily pigmented, or ventrally only very lightly pigmented. The antennae 2 segmented. Stemmata absent. 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 0 segmented, or 3 segmented. The labium without ligula between the palps. Labial palps present and segmented, or absent or non-segmented; when present, 1 segmented, or 2 segmented. Mesothoracic legs present and segmented, or much reduced or absent; 0 segmented, or 1–5 segmented; with 1 moveable claw. Visible abdominal segments 9, or 10. Tergum 9 of the abdomen entirely dorsal to extending to the underside. The abdomen having functional spiracles on anterior segments (biforous or bilabiate); 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, or not predacious (?); in decaying plant material, or in rotting wood, or under bark, or in the soil; the food sources uncertain.

The small-headed , legless larvae have greatly reduced mouthparts with mandibles biting outwardly as in Throscidae, very small antennae, and a subcylindric 9-segmented abdomen.

Classification. Suborder Polyphaga; Infraorder Elateriformia; Superfamily Elateroidea.

Representation in Britain and Ireland, and worldwide. About 1700 species worldwide. 6 species in Britain; genera in Britain 5; Dirhagus, Epiphanis, Eucnemis, Hylis, Melasis. E.g., Melasis buprestoides (Buprestis-like Melasis).

General comments. The adult prothorax (the first segment of the thorax) and the mesothorax (the second segment) are freely movable on one another, and the prosternal extension resembles that in Elateridae (q.v.), but the ‘clicking mechanism’ is apparently non-functional in this family..

Illustrations. • Melasis buprestoides (Buprestis-like Melasis: B. Ent. 055). • Melasis buprestoides (details, B. Ent. 055). • Melasis buprestoides: B. Ent. 055, legend+text. • Melasis buprestoides: B. Ent. 055, text cont.. • Eucnemus capucina and Melasis buprestoides (with Buprestidae, etc.): Fowler 4, 104 (1890). • Fowler 4, 104 (1890): original legend. • Dirhagus pygmaeus, with Elateridae: Fowler 4, 105 (1890).


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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