British insects: the families of Coleoptera
Adults. Beetles aquatic; 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; probably replenishing air for respiration beneath the elytra indirectly from that acquired and held in a ventral plastron (? - being ventrally hairy); perhaps incorporating bubbles of oxygen directly into the plastron (?). Body length/maximum body width 1.6–2.57; elytral length/pronotal length 1.77–3.62; 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; not necked; conspicuously waisted. Upper surfaces of body glabrous or subglabrous, or non-glabrous; not bristly; with neither scales nor scale-like setae.
Eyes not strongly protuberant; without bristles. Mandibles with a well developed mola. 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 maxillary palps conspicuously elongated, sometimes longer than the antennae. The maxillary palps conspicuously elongated, sometimes longer than the antennae. The apical segment of the maxillary palps cylindrical to fusiform. The apical segment of the labial palps not expanded apically. Antennae very short to about half the insect's head to tail length (perhaps with a respiratory function?); 7–11 segmented; clubbed. Antennal clubs 5 segmented (the club hairy); preceded by a cupule, or without a cupule. Antennal insertions hidden from above.
Prothorax without notopleural sutures. Pronotal length/maximum pronotal width 0.42–1.05. Metaventrite without a transverse groove. The fore-leg coxal cavities broadly open, or narrowly open, or broadly closed; narrowly separated; strongly transverse, or slightly transverse; with narrow lateral extensions, or without lateral extensions; internally open, or broadly closed internally. Tarsal segmentation formula 4, 4, 4. None of the tarsi with conspicuously bilobed segments. Some of the tarsi with a tiny basal segment that is hard to detect. The front tarsi with as many segments as the mid-tarsi; 5-segmented. Mid-leg tarsi 5-segmented; pentamerous, or pseudotetramerous. The claws of the mid-leg tarsi not appendaged. The claws of the mid-leg tarsi simple; without an associated empodium. Hind tarsi with at least as many segments as the mid-tarsi; 5-segmented; not flattened oar-like. Hind tarsi equipped with swimming hairs. Swimming hairs confined to the tarsi.
Elytral length/maximum width across the elytra 1.18–2. Elytra exposing no more than part of the terminal tergite. Scutellary striole absent. Wings well developed, or absent or much reduced; fringed with long hairs on the hind margin, or not fringed. Exposed abdominal sternites 7; all articulated and movable. Abdominal segment 8 with apparently functional spiracles.
Adults not predacious; phytophagous (on algae).
Larvae. The larvae campodeiform; elongate and more or less parallel-sided; vestiture restricted to fine hairs or setae; dorsally heavily pigmented or sclerotized, or only very lightly pigmented or sclerotized; only very lightly pigmented. The antennae 3 segmented; 0.15–0.5 x the head width, or more than 0.5 x the width of the head. Stemmata fewer than 6 (three or five). 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. The labial palps 3 segmented. The mesothoracic legs 5 segmented (including the pretarsus); with 1 movable claw. Visible abdominal segments 10. Tergum 9 of the abdomen entirely dorsal.
The larvae non-aquatic (living in wet places, but easily drowned). The abdomen exhibiting functional abdominal spiracles; having functional spiracles on anterior segments; with the spiracles on the eighth segment borne at the ends of spiracular tubes. The larvae without gills. Abdominal tergum 8 without amature. The larvae not predacious; phytophagous (on algae?).
Larvae subcylindric, active.
Worldwide and British representation. Genera at least 20. 29 species in Britain; genera in Britain 3; Hydraena, Limnebius, Ochthebius.
Classification. Suborder Polyphaga; Infraorder Staphyliniformia; Superfamily Staphilinoidea. E.g., Hydraena testacea (Testaceous Hydraena); Ochthebius punctatus (Irish Ochthebius); Ochthebius exsculptus (Gibson's Enicocerus).
General comments on this taxon. In Ochthebius, the thorax is strongly transverse and the last joint of the maxillary palps is much smaller than the penultimate one (being sometimes so small as to be hard to detect), while in Hydraena the thorax is quadrate to only slightly transverse, and the last joint of the palps is at least as long as the penultimate one.
Miscellaneous. • Hydraena testacea (Testaceous Hydraena: B. Ent. 307). • Hydraena testacea (details, B. Ent. 307). • Hydraena testacea: B. Ent. 307, legend+text. • Ochthebius punctatus (Irish Ochthebius: B. Ent. 250). • Ochthebius punctatus: B. Ent. 250, legend+text. • Ochthebius punctatus: B. Ent. 250, text cont.. • Ochthebius exsculptus (Gibson's Enicocerus): B. Ent. 291. • Ochthebius exsculptus: B. Ent. 291, legend+text. • Ochthebius exsculptus: B. Ent. 291, text cont.. • Hydraena britteni and Ochthebius subinteger, with Hydrophilidae and Staphylinidae: Fowler Suppl. 3, 1913. • Fowler Suppl. 3, 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. British insects: water beetles. Version: 18th September 2012. http://delta-intkey.com’.