British insects: the families of Coleoptera
British insects: the families of Coleoptera | |
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 somewhat 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. The maxillae with an outer palpiform lobe (the galea) additional to the 4-segmented maxillary palp. 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 immovably fixed to the metasternum and dividing the first abdominal sternite; much expanded and extended laterally to meet the elytra. Tarsal segmentation formula 5, 5, 5. The tarsi without bilobed segments; without ‘hidden’ segments. Front tarsi with as many segments as the mid-tarsi; 5-segmented (large). Mid-leg tarsi 5-segmented (much shorter than those of the fore-legs, flattened and oar-like); pentamerous. The claws of the mid-leg tarsi not appendaged. The claws of the mid-leg tarsi simple. Hind tarsi with as many segments as the mid-tarsi; 5-segmented; modified for swimming (much shorter than those of the fore-legs, flattened and oar-like). 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. Exposed abdominal sternites 6–7; comprising both fused and movable components; immovably joined 2, or 3. Abdominal segment 8 with apparently functional spiracles.
Adult 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 (finding food on the water surface with the aid of their specialized antennae).
Larvae. Larvae aquatic (the early stages living underwater, and breathing dissolved oxygen via gills; subsequently developing spiracles and pupating on land); entirely predacious.
Classification. Suborder Adephaga; Superfamily Caraboidea.
Worldwide and British representation. About 700 species worldwide. 13 species in Britain; genera in Britain 3; Aulonogyrus, Gyrinus, Orectochilus. E.g., Gyrinus bicolor (Elongated Whirl-wig or Whirligig Beetle).
General comments. Smooth, boat-shaped, surface-swimming beetles, with divided eyes which are adapted for simultaneously seeing above and below the water. Characteristically swimming rapidly in circles when alarmed.
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. • Gyrinus bicolor: B. Ent. 079, text cont..
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: 2nd January 2012. http://delta-intkey.com’.
