Insects of Britain and Ireland: the genera of Syrphidae (hoverflies)
Chrysogaster p.p., Orthoneura p.p.
Adult flies. The flies cupreous to bronze or bluish greenish; small; about 8 mm long. Wings 5.5–7 mm long.
The head somewhat wider than the thorax to about the same width as the thorax. The face entirely dark in ground colour; not elongated horizontally into a cone as long as the rest of the head. The frons not inflated. The eyes bare. Antennae relatively short, drooping; with their bases well separated (but seated on a tubercle); black, or ferruginous (?). The third antennal segment ovoid or orbicular. The antennal bristle dorsal; about as long as the third segment, or much longer than the third segment; simple.
The humeri hairy, and readily visible behind the head. The thorax pubescent without stiff bristles interspersed; patterned to plain; bright brassy, with longitudinal stripes (with a pair of fairly inconspicuous dark striae towards the front), or without longitudinal stripes. The scutellum flat, with a well defined edge. Wings plain (pale grey); without a conspicuously dark stigma; divergent in repose. Wing veins R2+3 and R4+5 not forming a closed cell. The anterior cross vein R-M in cell R5 crossing it before the middle of the adjoining discal cell to crossing it at or beyond the middle of the adjoining discal cell (near the middle). Vein R4+5 without a conspicuous curve projecting into the cell R5; without a backwardly projecting, incomplete transverse veinlet. The lower outer marginal vein markedly diverging from the posterior wing margin. The upper and lower outer marginal cross veins strongly stepped. The upper outer marginal cross-vein conspicuously bent near the base the base to conspicuously bent well above the base; bent at a sharp angle; not re-entrant (but almost re-entrant, as depicted by Falk). The alula distinct.
The abdomen wider than the thorax (in the female), or about the same width as the thorax (in the male); depressed, more or less oval (in the male), or ovate (in the female). The male abdomen with 4 visible segments. The abdomen not contrastingly patterned. Tergites 2–4 dulled dorsally. The spiracles of the third abdominal segment borne at or near the anterior corner of each side.
Larvae and pupae. The larvae tapering posteriorly; tailed. The anal segment tapered gradually to the spiracular process; shorter than the rest of the body. The larvae scarcely flattened; dark brown, plain; mouth without triangular sclerites; anal segments with lappets. The larvae more or less aquatic; saprophagous; in decaying vegetation (and mud, in still and slow-moving water).
General comments. The adults with a concave face leading smoothly to the projecting margin of the mouth; the face with the upper two thirds covered by a broad, straight white cross-band, with no shagreened area below. The larva is here assumed to resemble that of Orthonevra.
Classification. Subfamily Milesiinae; tribe Chrysogastrini.
British representation. 1 species in Britain (R. splendens). In marshes, fens and wet woodland locations across the British Isles.
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. Insects of Britain and Ireland: the genera of Syrphidae (hoverflies). Version: 28th July 2015. delta-intkey.com’.