British insects: the families of Coleoptera
British insects: the families of Coleoptera |
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= Pelobiidae.
Screech-beetles.
General appearance. 8.5–10 mm long. Body length/maximum body width 1.55–1.58. Elytral length/pronotal length 3.65–4.19. 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 oval to elongate-oval; dorsally strongly convex (convex above and below); not necked. Upper surfaces of body glabrous or subglabrous; not bristly; with neither scales nor scale-like setae.
Detailed morphology. Inclination of the head slight. Eyes strongly protuberant (by contrast with those of other water beetles); without bristles; finely facetted. The maxillae with an outer palpiform lobe (the galea) additional to the 4-segmented maxillary palp. Antennae very short; 11 segmented; filiform. Antennal insertions visible from above, or hidden from above. Mandibular prosthecae absent. Prothorax shorter than wide. Pronotal length/maximum pronotal width 0.4–0.5. Prothorax at its widest not markedly narrower than the adjoining part of the abdomen. Prothorax with notopleural sutures. Metaventrite with a transverse groove. Hind coxae immovably fixed to the metasternum and dividing the first abdominal sternite; not 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. Mid-leg tarsi 5-segmented; 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; longer than the tibiae, modified for swimming. Elytral length/maximum width across the elytra 1.22–1.26. Elytra exposing no more than part of the terminal tergite. Scutellary striole absent. Elytra glabrous. Wings well developed. Exposed abdominal sternites 6; comprising both fused and movable components; immovably joined 3. Abdominal segment 8 with apparently functional spiracles.
Adult habitat, ecology. Water-beetles; moving in the water by alternate, walking leg movements; predacious.
Larvae. Larvae aquatic; predacious.
Classification. Suborder Adephaga; Superfamily Caraboidea.
Worldwide and British representation. 5 species worldwide; genera 1 (a small monogeneric family, recorded from Europe, N. Africa, China and Australia). 1 species in Britain; genera in Britain 1; Hygrobia. E.g., H. hermanni.
General comments. Beetles stridulating loudly, by rubbing the apex of the abdomen on a file inside the elytra. Associated mainly with stagnant water..
Illustrations. • Hygrobia hermanni (Rye & Fowler III5).
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’.
