Insects of Britain and Ireland: the families of Coleoptera
General appearance. 2.5–5 mm long. Body length/maximum body width 1.7–3.05. Elytral length/pronotal length 2.2–3.53. 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; without ventral body cavities for reception of the legs; not necked; conspicuously waisted. Upper surfaces of body non-glabrous; not bristly; with neither scales nor scale-like setae.
Detailed morphology. Beetles prognathous. Inclination of the head slight. Eyes not strongly protuberant; without bristles; finely 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. The incisor edges of the mandibles with a single tooth, or 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 very short; strongly asymmetric; (9–)11 segmented. Antennal scape not swollen. Antennae clubbed. Antennal clubs 7 segmented (serrate); preceded by a cupule, or without a cupule. Antennal insertions visible from above; not in fossae.
Cervical sclerites present. Prothorax shorter than wide. Pronotal length/maximum pronotal width 0.52–0.82. The pronotum with lateral keels (pronotal carinae), or without lateral keels; keels if present, incomplete. 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; anteriorly simple; posteriorly narrowly rounded or acute. The prosternal process complete; moderately or strongly overlapping the mesoventrite. Metaventrite with a transverse groove. The fore-leg coxae countersunk in procoxal cavities. The fore-leg coxal cavities open behind externally; broadly open; narrowly separated; strongly transverse; without lateral extensions; internally open. The mid-leg coxae countersunk in mesocoxal cavities; separated by less than the shortest diameter of the cavity to 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; posteriorly shaped to receive the retracted femur; with a steep transverse declivity against which the femur retracts. Tarsal segmentation formula 4, 4, 4. The tarsi without bilobed segments; without hidden segments (but the terminal segment about half as long as the basal three together). Front tarsi with as many segments as the mid-tarsi; 4-segmented. Mid-leg tarsi 4-segmented; tetramerous; 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 1.18–2.3. Elytra exposing no more than part of the terminal tergite; not truncate; hard; non-glabrous (densely hairy). Elytra 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. Wings without an anal lobe. Wings without a medial fleck. Abdominal tergites 10. Abdominal sternites 5; comprising both fused and moveable components. Basal abdominal sternites immovably joined 3. Abdominal segment 8 with apparently functional spiracles. The male external genitalia not classified.
Adult habitat, ecology. Water-beetles, or land-dwellers (aquatic or sub-aquatic, in mud around streams and ponds, including brackish situations). Beetles walking in water or free-swimming by conventional ambulatory motion of the legs, not diving strongly. Moving in the water by alternate, walking leg movements. Beetles replenishing air for respiration beneath the elytra indirectly from that acquired and held in the ventral plastron; incorporating bubbles of oxygen directly into the plastron. Tunnelling in stiff mud at the sides of ponds and streams; phytophagous (feeding on algae).
Larvae. The larvae campodeiform; elongate and more or less parallel-sided. Body circular in cross-section to somewhat flattened. Vestiture restricted to fine hairs or setae. The larvae dorsally heavily pigmented or sclerotized; ventrally only very lightly pigmented. The antennae 3 segmented; less than 0.15 x the width of the head. Stemmata present; on either side of the larval head 6. The larval fronto-clypeus not extended forwardly. The frontoclypeal suture between frons and clypeus distinct. The labrum and head capsule separated by a complete 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 or cribriform); without spiracular tubes. The larvae without abdominal gills. The abdominal apex without a respiratory chamber. Abdominal tergum 8 without amature. The last abdominal segment without cerci.
Larvae seemingly non-aquatic; burrowing in wet sand or mud alongside water; phytophagous and consuming decaying plant material (digesting algae and other organic materials which are ingested with quantities of the substrate).
The larvae elongate, with rather distended thoracic segments, well developed legs, and 10 visible abdominal segments.
Classification. Suborder Polyphaga; Infraorder Elateriformia; Superfamily Dryopoidea.
Representation in Britain and Ireland, and worldwide. About 250 species worldwide; genera 5–20 (depending on taxonomic opinion). 8 species in Britain; genera in Britain 1; Heterocerus. E.g., Heterocerus obsoletus (Largest Heterocerus).
Illustrations. • Heterocerus obsoletus Curtis (Largest Heterocerus: B. Ent. 224). • Heterocerus obsoletus (details, B. Ent. 224). • Heterocerus obsoletus (B. Ent. 224, legend+text). • Heterocerus obsoletus (B. Ent. 224, text cont.). • Heterocerus fenestratus, H. flexuosus, H. fusculus and H. maritimus: (with Elmidae and Dryopidae): Fowler 3, 98 (1889). • Fowler 3, 98 (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. delta-intkey.com’.