British insects: the families of Coleoptera
Adults. Beetles sub-aquatic, or aquatic (? - the rare British representative having been found on sticks submerged in a water course); presumably 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; when submerged, presumably replenishing air for respiration beneath the elytra indirectly from that acquired and held in a ventral plastron (?); perhaps incorporating bubbles of oxygen directly into the plastron (?). Beetles 1.5–2 mm long; body length/maximum body width 1.35–1.77; elytral length/pronotal length 2.8–4.57; 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, or distinctly narrower than greatest elytral width. Beetles oval; dorsally strongly convex; not necked; not waisted; black or dark brown. Upper surfaces of body non-glabrous; not bristly; with neither scales nor scale-like setae. Inclination of the head slight to strong.
Eyes two; strongly protuberant; without bristles; finely facetted. Mandibles without a mola; without prosthecae. The mandibular apices simple. The incisor edges of the mandibles simple. The maxillae with distinct galea and lacinia apically to the palp. The maxillary palps not especially elongated. The apical segment of the maxillary palps somewhat expanded and truncate to subtriangular. The apical segment of the labial palps more or less expanded apically. Antennae long, but not exceeding the insects head to tail length; inserted on the front of the head, with the distance between their bases no greater than the length of their first segment; not strongly asymmetric; 11 segmented. Antennal scape not swollen. Antennae finely serrate.
Prothorax shorter than wide; at its widest not markedly narrower than the adjoining part of the abdomen; without notopleural sutures. Pronotal length/maximum pronotal width 0.3–0.55. Metaventrite with a transverse groove. Mid-and hind-legs not as in Gyrinidae (q.v.). The fore-leg coxal cavities broadly open; narrowly separated; strongly transverse; without lateral extensions; internally open. Hind coxae not extended laterally to meet the elytra; posteriorly shaped to receive the retracted femur. The hind coxae not produced behind into flat plates partly concealing the hind femora. Hind coxae with a steep transverse declivity against which the femur retracts. The inner parts (processes) of the hind coxae not incorporated with the metasternum in a flat, median longitudinal keel. 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 with an appendage, or not appendaged; appendages when present, not or only lightly sclerotized. 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.
Elytral length/maximum width across the elytra 1.05–1.38. Elytra exposing no more than part of the terminal tergite; hard. Scutellary striole present (associated with a prominence near the scutellum). Elytra non-glabrous (shortly, finely and densely hairy). Wings well developed. Exposed abdominal sternites 5–6; comprising both fused and movable components; immovably joined 3. Abdominal segment 8 apparently without functional spiracles.
Aquatic or sub-aquatic to terrestrial: found in moist places under grass, etc., sometimes in water.
Larvae. The larvae strongly flattened and disc-like (characteristically disc-shaped water pennies, with head, legs and gills hidden from above by broad marginal extensions from all the segments); oblong to ovate; vestiture not restricted to fine hairs or setae; dorsally heavily pigmented or sclerotized; only very lightly pigmented. The antennae 3 segmented; more than 0.5 x the width of the head. Stemmata 6. Frontoclypeal suture between frons and clypeus distinct. The labrum and head capsule separated by a complete suture. Apices of the mandibles with a single lobe or tooth. The maxillary palps 3 segmented, or 4 segmented. The labium with a ligula at least as long as the palps. The labial palps 3 segmented, or 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 (found clinging to stones). The abdomen exhibiting functional abdominal spiracles (?); having functional spiracles on anterior segments, or with functional spiracles confined to the the eighth segment; with the spiracles on the eighth segment borne at the ends of spiracular tubes (?). The larvae with anal gill tufts. Abdominal tergum 8 without amature. The larvae predacious (e.g., on other larvae), or not predacious; when not predaceous, phytophagous (e.g., on algae), or coprophagous.
Worldwide and British representation. 1 species in Britain (E. palustris). Recorded from very local, Northern England, South-west England and Wales, and South-eastern England.
Classification. Suborder Polyphaga; Infraorder Elateriformia; Superfamily Dryopoidea; Psephenidae.
General comments on this taxon. Beetles black or pitchy red, with the legs and first antennal segment yellow.
Miscellaneous. • Eubria palustris: Fowler 4 (1890). • Eubria palustris (from Joy). Limnichus pygmaeus (Limnichidae). Eubria palustris (Psephenidae).
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’.