British Insects: the Families of Coleoptera
British Insects: the Families of Coleoptera |
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Whirligig beetles.
General appearance. 3.7–7.4 mm long. Body length/maximum body width 1.4–1.98. Elytral length/pronotal length 3.1–4.95. 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 more or less convex to dorsally strongly convex; not necked; not waisted; very dark, blue or olive green. Upper surfaces of body glabrous or subglabrous, or non-glabrous; not bristly; with neither scales nor scale-like setae.
Detailed morphology. Inclination of the head slight. Eyes ostensibly four; not strongly protuberant; without bristles. Antennae very short; 8–11 segmented; clubbed. Antennal clubs preceded by a cupule, or without a cupule. Antennal insertions visible from above, or hidden from above. Mandibular prosthecae absent.
Prothorax shorter than wide. Pronotal length/maximum pronotal width 0.3–0.53. Prothorax at its widest not markedly narrower than the adjoining part of the abdomen. Prothorax with notopleural sutures. Metaventrite with a transverse groove, or without a transverse groove. Mid-and hind-legs oar-like and much shorter than the fore-legs, which are elongated and modified for grasping prey. Hind coxae immoveable. The tarsi without bilobed segments; without ‘hidden’ segments. Mid-leg tarsi 5-segmented (much shorter than those of the fore-legs, flattened and oar-like); pentamerous. Claws of the mid-leg tarsi not appendaged. Front tarsi with as many segments as the mid-tarsi; 5-segmented (large). Hind tarsi with as many segments as the mid-tarsi; modified for swimming (much shorter than those of the fore-legs, flattened and oar-like). Tarsal claws simple. Elytral length/maximum width across the elytra 1.15–1.54. Elytra exposing no more than part of the terminal tergite to at least one but fewer than three complete abdominal tergites; glossy. Scutellary striole absent. Wings well developed.
Visible abdominal sternites 6–7; immovably joined 2, or 3. Abdominal segment 8 with apparently functional spiracles.
Habitat, ecology. Water-beetles (on the water's surface, conspicuously gregarious); ‘rowing’ by parallel-simultaneous leg movements (on the surface of the water, in colonies, with characteristic whirling motion); largely predacious.
General comments. Smooth, boat-shaped beetles.
Larvae. Larvae aquatic; entirely predacious.
Classification. Suborder Adephaga; Superfamily Caraboidea.
British representation. Genera 3; 13 species. E.g., Gyrinus bicolor (Elongated Whirl-wig or Whirligig Beetle).
Illustrations. • Gyrinus bicolor (Elongated Whirl-wig or Whirligig beetle: B. Ent. 079). • Gyrinus bicolor (details, B. Ent. 079). • Gyrinus bicolor: B. Ent. 079, legend+text.
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: 9th June 2008. http://delta-intkey.com’.
