British insects: the families of Coleoptera

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L. Watson and M. J. Dallwitz

Hydraenidae

= Limnebiidae.

Crawling Water-beetles.

General appearance. (0.75–)1.1–1.7(–2.5) mm long. 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. The underside without a plastron of hydrofuge hairs.

Detailed morphology. Eyes not strongly protuberant; without bristles. The maxillary palps conspicuously elongated, sometimes longer than the antennae. 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. Pronotal length/maximum pronotal width 0.42–1.05. Prothorax without notopleural sutures. Metaventrite without a transverse groove. The mid-leg cavities open laterally. Hind-leg coxae extending laterally to meet the elytra. Tarsal segmentation formula 4, 4, 4. The tarsi without bilobed segments; with a tiny basal segment that is hard to detect. Front tarsi with as many segments as the mid-tarsi; 5-segmented. Mid-leg tarsi 5-segmented; pentamerous, or pseudotetramerous (the basal one), or tetramerous. The claws of the mid-leg tarsi not appendaged. The claws of the mid-leg tarsi simple; without an associated empodium. Hind tarsi with as many segments as the mid-tarsi; 5-segmented; not flattened and oar-like. 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 (6–)7; all articulated and moveable. Abdominal segment 8 with apparently functional spiracles.

Adult habitat, ecology. All or mostly? water-beetles. 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; not noticeably posing regularly at the water surface to replenish air; incorporating bubbles of oxygen directly into the plastron. Occurring in various aquatic, semi-aquatic, riparian and littoral habitats; phytophagous, or phytophagous and consuming decaying plant material (feeding principally on algae?).

Larvae. Mature larvae minute (less than 3 mm long). The larvae campodeiform; elongate and more or less parallel-sided. Body somewhat flattened. Vestiture restricted to fine hairs or setae. The larvae dorsally heavily pigmented or sclerotized, or dorsally only very lightly pigmented or sclerotized; ventrally 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 present; on either side of the larval head 3, or 5. 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); with the spiracles on the eighth segment borne at the ends of spiracular tubes, or without spiracular tubes. The larvae without abdominal gills. The abdominal apex without a respiratory chamber. Abdominal tergum 8 without amature. The last abdominal segment with cerci.

Larvae non-aquatic (living in wet places, but easily drowned); not predacious, or predacious and not predacious (?); found in assorted aquatic and littoral habitats, cf. the adults; phytophagous (perhaps mainly on algae, but some predacious and saprophagous behaviour has been reported in the family).

Larvae subcylindric, active, with 10 abdominal segments.

Classification. Suborder Polyphaga; Infraorder Staphyliniformia; Superfamily Staphilinoidea.

Worldwide and British representation. Genera at least 20. 29 species in Britain; genera in Britain 3; Hydraena, Limnebius, Ochthebius. E.g., Hydraena testacea (Testaceous Hydraena); Ochthebius punctatus (Irish Ochthebius); Ochthebius exsculptus (Gibson's Enicocerus).

Illustrations. • 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: the families of Coleoptera. Version: 25th July 2012. http://delta-intkey.com’.

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