British insects: the families of Coleoptera
= Elmididae, Elminthidae, Helmidae, Helminthidae, Limniidae.
Riffle Beetles, Water-beetles.
Adults. Beetles aquatic (in running water, found under stones and logs); 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; replenishing air for respiration beneath the elytra indirectly from that acquired and held in a ventral plastron; incorporating bubbles of oxygen directly into the plastron. Beetles 1.3–4.75 mm long; body length/maximum body width 1.8–3.1; elytral length/pronotal length 1.8–4.7; 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 oval to elongate-oval; without ventral body cavities for reception of the legs; not necked; somewhat waisted; conspicuously long-legged; exhibiting bright warning colours, or without warning colouration. Upper surfaces of body glabrous or subglabrous, or non-glabrous; not bristly; with neither scales nor scale-like setae. Inclination of the head slight to strong.
Eyes not strongly protuberant; without bristles. Mandibles with a well developed mola. The mandibular apices bidentate or bilobed, or multidentate or multilobed. 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 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; 7–11 segmented. Antennal scape not swollen. Antennae filiform. Antennal insertions visible from above; not in fossae.
Prothorax without notopleural sutures. Pronotal length/maximum pronotal width 0.6–1.1. The scutellum elevated. Metaventrite with a transverse groove. The fore-leg coxal cavities broadly open; quite widely separated; strongly transverse, or slightly transverse, or circular to longer than wide; without lateral extensions; internally open. Hind coxae posteriorly shaped to receive the retracted femur; with a steep transverse declivity against which the femur retracts. Tarsal segmentation formula 5, 5, 5. None of the tarsi with conspicuously bilobed segments. None of the tarsi with hidden segments. The front tarsi with as many segments as the mid-tarsi; 5-segmented. Mid-leg tarsi 5-segmented; pentamerous. The claws of the mid-leg tarsi not appendaged. The claws of the mid-leg tarsi simple, or one-toothed or bifid. Hind tarsi with at least as many segments as the mid-tarsi; 5-segmented (the elongate last segment bulbous at the tip).
Elytral length/maximum width across the elytra 1.3–2.5. Elytra exposing no more than part of the terminal tergite; not truncate. Scutellary striole present, or absent. Wings well developed, or absent or much reduced. Exposed abdominal sternites 5–6; comprising both fused and movable components; immovably joined 3. Abdominal segment 8 with apparently functional spiracles, or apparently without functional spiracles.
Adults not predacious; phytophagous; in living vegetation.
Larvae. The larvae campodeiform; elongate and more or less parallel-sided; vestiture restricted to fine hairs or setae, or not restricted to fine hairs or setae; only very lightly pigmented or sclerotized; more or less heavily pigmented. The antennae 3 segmented; 0.15–0.5 x the head width. Stemmata fewer than 6 (one or five). Apices of the mandibles bilobed or bidentate, or trilobed or tridentate. The maxillary palps 4 segmented. The labium with a short ligula between the palps, or with a ligula at least as long as the palps. The labial palps 4 segmented. The mesothoracic legs 5 segmented (including the pretarsus); with 1 movable claw. Visible abdominal segments 10. Tergum 9 of the abdomen extending to the underside.
The larvae aquatic. The abdomen exhibiting functional abdominal spiracles, or without functional spiracles; having functional spiracles on anterior segments, or with functional spiracles confined to the the eighth segment. The larvae with anal gill tufts. Abdominal tergum 8 without amature. The larvae not predacious; phytophagous; on living vegetation.
Larvae woodlouse-shaped or cylindric, with three tufts of retractive anal gills.
Worldwide and British representation. Genera about 30 (?). 11 species in Britain; genera in Britain 8; Elmis, Esolus, Limnius, Macronychus, Normandia, Oulimnius, Riolus, Stenelmis.
Classification. Suborder Polyphaga; Infraorder Elateriformia; Superfamily Dryopoidea. E.g., Limnius volkmari (Volckmar's Elmis Water-beetle).
Miscellaneous. • Limnius volckmari (Volckmar's Water-beetle: bent294). • Limnius volckmari (details, B. Ent. 294). • Limnius volckmari: B. Ent. 294, legend+text. • Elmis aenea, Esolus, Limnius, Macronychus, Oulimnius (with Dryopidae, Heteroceridae and Hydrophilidae): 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. British insects: water beetles. Version: 18th September 2012. http://delta-intkey.com’.