British insects: the families of Coleoptera


L. Watson and M. J. Dallwitz

Dryops Oliver

Adults. Beetles terrestrial to sub-aquatic, or aquatic (under stones, etc., in or close to water); 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; perhaps 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 3.5–5.5 mm long; body length/maximum body width 1.7–3.2; 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 without ventral body cavities for reception of the legs; not necked. Upper surfaces of body non-glabrous; with neither scales nor scale-like setae. Inclination of the head slight to strong.

Eyes two; strongly protuberant, or not strongly protuberant; bristly, or without bristles. Mandibles with a well developed mola. The maxillae with distinct galea and lacinia apically to the palp; without stylet-like lobes. The maxillary palps not especially elongated. The apical segment of the maxillary palps cylindrical to fusiform. The apical segment of the labial palps not expanded apically. Antennae very short, or short; not strongly asymmetric. Antennal scape not swollen. Antennae clubbed and pectinate (of unusual form, with a pectinate club). Antennal clubs 6–10 segmented (‘six or more’). Antennal insertions visible from above, or hidden from above; not in fossae.

Prothorax without notopleural sutures. Pronotal length/maximum pronotal width 0.4–1.05. The pronotum with a pair of short longitudinal furrows, one on each side (markedly contracted in front). The scutellum elevated. Metaventrite with a transverse groove, or without a transverse groove. Mid-and hind-legs not as in Gyrinidae (q.v.). The fore-leg coxal cavities broadly open; quite widely separated; strongly transverse; without lateral extensions; internally open. Hind coxae not extended laterally to meet the elytra; not shaped posteriorly to receive the 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 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. Hind tarsi without ‘swimming’ hairs.

Elytral length/maximum width across the elytra 1.1–2.3. Elytra exposing no more than part of the terminal tergite; hard. Scutellary striole absent. Elytra non-glabrous (covered with fine hairs, which unlike those of Pomatinus are more or less raised). Exposed abdominal sternites 5; comprising both fused and movable components; immovably joined 2. Abdominal segment 8 with apparently functional spiracles.

Adults not predacious; close to fresh water. “Under stones, etc., in or close to water” (Joy).

Larvae. The larvae campodeiform; elongate and more or less parallel-sided; vestiture restricted to fine hairs or setae; dorsally heavily pigmented or sclerotized; more or less heavily pigmented. The antennae 3 segmented; less than 0.15 x the with of the head, or 0.15–0.5 x the head width. Stemmata 6. Frontoclypeal suture between frons and clypeus distinct. The labrum and head capsule separated by a complete suture. Apices of the mandibles trilobed or tridentate. The maxillary palps 4 segmented. The labium with a short ligula between 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 entirely dorsal.

The larvae aquatic to non-aquatic. The abdomen having functional spiracles on anterior segments. The larvae without gills. Abdominal tergum 8 without amature. The larvae not predacious; consuming decaying plant material and consuming rotting wood (in wet soil and leaf litter, and waterlogged wood).

Worldwide and British representation. 7 species in Britain. Recorded from Scotland, Northern England, South-west England and Wales, South-eastern England, and Ireland.

Classification. Suborder Polyphaga; Infraorder Elateriformia; Superfamily Dryopoidea; Dryopidae.

Miscellaneous. • Dryops luridus (Impressed Parnus: B. Ent. 080). • Dryops luridus (details, B. Ent. 080). • Dryops luridus: B. Ent. 080, legend+text. • Dryops luridus: B. Ent. 080, text cont.. • Dryops (7 spp.), with unrelated taxa: Fowler Suppl. 14, 1913. • Fowler 6, 14 (1913): original legend.. • Dryops auriculatus and Pomatinus, with Elmidae and Heteroceridae: Fowler 3, 98 (1889). • Fowler 3, 98 (1889): original legend..

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Cite this publication as: ‘Watson, L., and Dallwitz, M.J. 2003 onwards. British insects: water beetles. Version: 18th September 2012.’.