Bracteon Bedel, 1879
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ADEPHAGA Clairville, 1806
BEMBIDIINI Stephens, 1827
B. argenteolum (Ahrens, 1812)
B. litorale (Olivier, 1790)
Formerly referred to as Chrysobracteon Netolitzky, 1914, and variously classified as a subgenus of Bembidion Latreille, 1802. It is now (variously) considered to be a distinct genus based on both larval and adult features. A small genus of Palaearctic and Nearctic carabids; 17 species have been described of which 12 are Nearctic. Among the Bembidiini they are characterized by the dilated third elytra interval which has opaque, strongly microsculptured areas surrounding each dorsal puncture, alternating with these are several slightly raised and brilliantly metallic areas sometimes called mirrors. The largest member of the genus is Bracteon argenteolum (Ahrens, 1812). Typical habitat is sandy or gravelly margins of freshwater rivers and lakes. These habitats are usually devoid of vascular plants although some species seem to prefer sparsely vegetated margins. Most species are diurnal but they have also been found active at night. All species are fully winged and on warm, sunny days they are very active and quick to take flight so making them difficult to sample. They are often found in large numbers where they occur. Two species occur in the U.K. and are easily separated:
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Third and fourth elytral stria straight. Pronotum transverse. Larger, 5.8-7.5mm.
Bracteon argenteolum (Ahrens, 1812)
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Third and fourth elytral striae curved in front of shiny area on third elytral interval. Pronotum quadrate, or nearly so. Smaller and more convex, 5.6-6.2mm.
Bracteon litorale (Olivier, 1790)
Bracteon litorale (Olivier, 1790)
Widely distributed and locally common throughout Europe; from France east through Ukraine, Kazakhstan and Russia, and north to Scandinavia. In the U.K. a very local species in northern Scotland and England north of the Humber. Elsewhere there are a few scattered records from southern England and the Welsh borders. They occur on fine shingle and sand beside rivers and lakes where the vegetation is sparse and low. Adults are active between April and August and may be abundant when found.
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Entire upper surface, legs, palps and basal antennal segments metallic. Head dull from dense granular microsculpture. Eyes large and prominent. Frontal furrows extended onto clypeus. Labrum shiny; its microsculpture much finer than that on the head. First antennal segment pale beneath. Pronotum quadrate or slightly transverse and broadest around the middle. Strongly sinuate before obtuse hind angles. Front and hind margins not bordered. Hind margin produced backwards. Basal fovea small but deep. Central longitudindal impression strong. Microsculpture finer than that on the head. Lateral margin of elytra not continued past humeral angle. Third interstice with two rectangular coarsely microsculptured areas around the punctures, this microsculpture is also present around the elytral margins and apex. In some lights these areas appear silver. Cuticle around and between these areas, and in discreet areas in the outer interstices, appearing slightly raised and shiny, what Lindroth referred to as ‘mirrors’. Elytra otherwise entirely and quite strongly microsculptured. All striae strongly punctured and continued to, or almost to, apex. Fourth stria abruptly curved in basal third. Legs entirely dark.
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Bracteon argenteolum (Ahrens, 1812)
Locally common throughout Europe east to Kazakhstan, Ukraine and Russia, and north to Scandinavia. In the U.K. formerly occurred only at Lough Neagh in Ireland but disappeared in the nineteen thirties after the fluctuating water levels were stabilized. A single record from the south coast (Dungeness, Kent) in 1991 was probably a continental vagrant. Now known only from a breeding population beside a silt lagoon in an actively worked sand and gravel quarry near Cavenham in west Suffolk.
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Upper surface entirely metallic. Head with dense granular microsculpture. Eyes large and prominent. Frontal furrows extended onto clypeus. Microsculpture on labrum stronger than that on the head. First antennal segment pale. Pronotum transverse and widest near middle. Sides strongly sinuate before obtuse hind angles. Front margin not bordered. Hind margin bordered to deep, longitudinal basal fovea, without margin medially. Finely punctured in front of hind margin. Microsculpture fine on disc. Lateral elytral margin angled over humerus and not continued onto basal margin. Third interstice with two rectangular strongly microsculptured fields around the dorsal punctures, the areas around these more finely microsculptured, and shiny. Striae punctured, less strongly so towards apex. Fourth stria more or less straight. Femora and tarsi dark metallic, tibiae pale.