Insects of Britain and Ireland: the genera of Syrphidae (hoverflies)
Adult flies. The flies metallic blackish to greenish bronze; minute to small; about 4–7 mm long. Wings 4–6.25 mm long.
The head slightly wider than the thorax to about the same width as the thorax. The face without a central knob; almost produced below and extending beyond the antennae, or not extending below beyond the antennae; not elongated horizontally into a cone as long as the rest of the head. Antennae relatively short, drooping; with their bases well separated (on a tubercle); black, or ferruginous. The third antennal segment ovoid or orbicular. The antennal bristle dorsal; simple (bare).
The humeri hairy, and readily visible behind the head. The thorax pubescent without stiff bristles interspersed; patterned to plain; with longitudinal stripes (with two longitudinal dust stripes on the dorsum), or without longitudinal stripes. The scutellum black, or aeneous. Wings patterned to plain (slightly grey, sometimes clouded dark in the disc); with a conspicuous dark stigma; incumbent and almost parallel 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. 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 well above the base; bent at a sharp angle; re-entrant (e.g., O. nobilis), or not re-entrant. The alula distinct to indistinct.
The abdomen much wider than the thorax; depressed, broadly to narrowly oval, or ovate, or oblong. 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; 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).
General comments. The adults with a concave face leading smoothly to the projecting margin of the mouth.
Classification. Subfamily Milesiinae; tribe Chrysogastrini.
British representation. 3 species in Britain.
Illustrations. • O. brevicornis and O. nobilis: Verrall. • 15 genera (from Walker). • 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’.