Insects of Britain and Ireland: the genera of Syrphidae (hoverflies)
Adult flies. The flies sphecid wasp-like (cf. Pemphredon and Psenulus); dark or blackish, sometimes marked yellowish to reddish; minute to small; slender, elongate, 5–9 mm long. Wings 4.75–7 mm long.
The head wider than the thorax to about the same width as the thorax. The face without a central knob. The eyes depicted as bare. Antennae relatively short, drooping; black, or tawny. The third antennal segment ovoid or orbicular. The antennal bristle dorsal; simple (bare).
The humeri hairy, and readily visible behind the head. The thorax plain; without longitudinal stripes. Wings plain (slightly grey in S. clunipes); without a conspicuously 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. 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 well above the base; curved on the bend; joining vein R4+5 almost at right angles, so that cell R5 is not extended towards the wing tip; not re-entrant. The alula indistinct.
The abdomen at the widest (posterior) part about the same width as the thorax, or narrower than the thorax; clavate; conspicuously proximally petiolated (segment 2 being narrow-elongate, with 3 and 4 broadened); contrastingly patterned (in males), or not contrastingly patterned. The tergite patterning involving 3 (only), or 3 and 4. The colour-patterned tergites marked with yellow to tawny (to reddish?). The tergite bands entire; wide.
Larvae and pupae. The larvae tapering posteriorly; shortly tailed. The anal segment tapered gradually to the spiracular process. The larvae dorso-ventrally flattened (6–8 mm long, with small prolegs); pale brown, plain; without thoracic hooks; mouth without triangular sclerites; anal segments with lappets. The larvae saprophagous; in sap runs and in decaying sap under loose bark.
General comments. The adults with a concave face leading smoothly to the projecting margin of the mouth.
Classification. Subfamily Milesiinae; tribe Chrysogastrini.
British representation. 4 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’.