Insects of Britain and Ireland: the genera of Syrphidae (hoverflies)
Adult flies. The flies muscid-like; black with greenish or purplish sheen; small; 5.6–7.9 mm long. Wings 5.25–7.25 mm long.
The head wider than the thorax to about the same width as the thorax. The face entirely dark in ground colour; not flat or retreating between antennae and mouth; with a central knob to without a central knob; not elongated horizontally into a cone as long as the rest of the head; with tubercles, or without tubercles. The frons markedly inflated, or not inflated. The eyes bare; not rimmed along their facial borders for much of the height of the face. Antennae relatively short, drooping; with their bases well separated (but seated on a tubercle); ferruginous. The third antennal segment ovoid or orbicular. The antennal bristle dorsal; much longer than the third segment; simple (bare).
The humeri hairy, and readily visible behind the head. The thorax pubescent without stiff bristles interspersed; plain (bronze); without longitudinal stripes. The scutellum flat, with a well defined edge; aeneous, or black. Wings plain (usually rather dark, or darkening distally); divergent in repose; with a vena spuria to apparently without a vena spuria. 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. Vein R4+5 without a conspicuous curve projecting into the cell R5; without a backwardly projecting, incomplete transverse veinlet. Vein R without bristles. 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; not re-entrant (but more or less at right angles). The alula distinct.
The abdomen about the same width as the thorax; oblong to obovate (depressed). 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. The larvae scarcely flattened; brown, plain; without thoracic hooks; 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).
Classification. Subfamily Milesiinae; tribe Chrysogastrini.
British representation. 3 species in Britain.
Illustrations. • 18 genera (from Walker).
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’.