Insects of Britain and Ireland: the families of Coleoptera
Including Cebrionidae, Cavicoxumidae, Dicronychidae, Lissomidae, Throscidae part.
Click-beetles, Skip-jack beetles, Wire-worms.
General appearance. 2.8–30 mm long (?). Body length/maximum body width 1.73–5.16. Elytral length/pronotal length 1.3–6. 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 elongate to slender; not necked; not waisted. 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. Beetles clicking and jumping to right themselves when inverted (flexing violently at the junction of the pro- and mesothorax).
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 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, or without a mola; with well developed prosthecae to 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. The apical segment of the maxillary palps variously cylindrical to fusiform, or somewhat expanded and truncate to subtriangular, or securiform to cultriform. The apical segment of the labial palps more or less expanded apically, or not expanded apically. Antennae short to long, but not exceeding the insects head to tail length; 11(–12) segmented. Antennal scape not swollen. Antennae filiform, or serrate, or pectinate (occasionally plumose). 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 to longer than wide. Pronotal length/maximum pronotal width 0.4–1.35. The pronotum with lateral keels (pronotal carinae) (mostly), or without lateral keels; keels when present, complete, or incomplete. Posterior edge of the pronotum distinctly crenulate, or not crenulate. Prothorax at its widest not markedly narrower than the adjoining part of the abdomen. Prothorax without notopleural sutures. Scutellum conspicuous; elevated above the mesoscutum in lateral view, or not elevated; anteriorly simple, or notched; posteriorly narrowly rounded or acute, or broadly rounded or obtusely angulate, or truncate. The prosternal process complete; consistently 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 to narrowly open; narrowly separated, or quite widely separated (mostly); circular to longer than wide; without lateral extensions; internally open, or internally closed by a slender bar (some Elaterinae). 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 narrowly separated, or moderately to widely separated; not or scarcely oblique; open laterally, or closed 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 usually 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 sometimes with three or more setae). Hind tarsi with as many segments as the mid-tarsi; 5-segmented.
Elytral length/maximum width across the elytra 1–3.83. Elytra exposing no more than part of the terminal tergite to at least three complete abdominal tergites; hard. Elytra with six or more longitudinal lines of punctures, or 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, or absent or much reduced. Wings variously with an anal lobe, or without an anal lobe. Wings without a medial fleck. Abdominal sternites 5; comprising both fused and moveable components. Basal abdominal sternites immovably joined 2–4 (segment 5 being movable). Abdominal segment 8 with apparently functional spiracles. The male external genitalia trilobate.
Adult habitat, ecology. Land-dwellers; seemingly mostly not predacious; often on living vegetation (or on bark).
Larvae. Mature larvae minute (less than 3 mm long), or small to medium-sized, or relatively large. The larvae elongate and more or less parallel-sided. 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 3 segmented. Stemmata present (sometimes), or absent (commonly); on either side of the larval head when present, 1. 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, or bilobed or bidentate. The maxillary palps 4 segmented. The labium without ligula between the palps, or 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 (in British representatives). Tergum 9 of the abdomen 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 (commonly), or not predacious (especially soil-dwelling forms); in living vegetation, or in decaying plant material, or in rotting wood, or in dried plant material, or under bark, or under stones, or in stored plant products, or in the soil (i.e., in divers habitats); when non-predacious, usually phytophagous (Agrypninae and Elaterinae including pests familiar as wireworms in grass and root crops).
The larvae wiry-bodied, with the labrum absent or fused to the clypeus, and abdominal segment 9 conical.
Classification. Suborder Polyphaga; Infraorder Elateriformia; Superfamily Elateroidea.
Representation in Britain and Ireland, and worldwide. About 9300 species worldwide; genera at least 900. 65 species in Britain; genera in Britain 26; Agrypnus, Cardiophorus, Denticollis, Elater, Megapenthes, Negastrius, etc. E.g., Elater sanguinolentus; Megapenthes lugens.
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 underside of the former bears a pointed, rearward prosternal extension which engages and disengages with a cavity in the under-side of the latter. This arrangement constitutes the familiar clicking mechanism, whereby the beetle clicks and jumps to right itself or as a means of escape. The labrum protrudes forwards of the front of the head, and unlike the situation in Eucnemidae it is visible from above..
Illustrations. • Ampedus sanguinolentus (Rye & Fowler IX1). • Megapenthes lugens: B. Ent. 694. • Megapenthes lugens: B. Ent. 694, legend+text. • Megapenthes lugens: B. Ent. 694, text cont.. • Megapenthes lugens(Janson 184). • Agriotes, Athous and Corymbites: Curtis (1860, Plate F). • Agriotes, Athous and Corymbites: Curtis (1860, legend). • Agriotes, Athous and Corymbites: Curtis (1860, legend cont.). • Assorted Click-beetles: Curtis (1860, Plate G). • Agrypnus, Cardiophorus, Cryptohypnus, Elater (3 spp.), Fleutiauxellus, Hypnoidus, Negastrius, Zorochros (with Dirhagus): Fowler 4, 105 (1890). • Fowler 4, 105 (1890): original legend.. • Elater (6 spp.), Ischnodes, Megapenthes, Melanotus (3 spp.), Procraerus: Fowler 4, 106 (1890). • Fowler 4, 106 (1890): original legend.. • Adrastus, Athous (7 spp.), Cidnopus (2 spp.), Sericus, Synaptus: Fowler 4, 107 (1890). • Fowler 4, 107 (1890): original legend.. • Adrastus, Agriotes (4 spp.), Anostirus, Ctenicera, Dalopius, Selatosomus: Fowler 4, 108 (1890). • Fowler 4, 108 (1890): original legend.. • Denticollis (2 spp.), Prosternon, Selatosomus (5 spp, with Dascillidae and Scirtidae): Fowler 4, 109 (1890). • Fowler 4, 109 (1890): original legend.. • Athous, Cardiophorus and Negastrius, with unrelated taxa: Fowler Suppl. 15, 1913. • Fowler Suppl. 15, 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’.