Insects of Britain and Ireland: the genera of Syrphidae (hoverflies)
Adult flies. The flies vespid wasp-like (especially S. silentis, cf. Dolichovespula and Vespula); black with yellow markings; medium sized to large; 12–16 mm long. Wings 9.25–14 mm long.
The head slightly wider than the thorax to about the same width as the thorax. The face ground-coloured at least part yellow; not flat or retreating between antennae and mouth; with a central knob. The eyes bare. Antennae relatively short, drooping; with their bases well separated; black, or ferruginous (?). The third antennal segment ovoid or orbicular. The antennal bristle dorsal; much longer than the third segment; plumose.
The humeri hairy, and readily visible behind the head. The thorax pubescent without stiff bristles interspersed; patterned (with a pair of anterior pale spots), or plain (?); without longitudinal stripes. The scutellum brownish, ferrugineous or tawny (ferrugineous). Wings plain (grey, tinted somewhat ferrugineous or tawny basally and along the costa, sometimes clouded brown at the tips); 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 more or less parallel with the posterior wing margin. The upper outer marginal cross-vein gently curved; not re-entrant. The alula distinct.
The abdomen wider than the thorax; obovate (in the female), or oval, or obovate (in the male); contrastingly patterned. The tergite patterning involving 2 to 4. The colour-patterned tergites marked with whitish to yellow, or tawny. The tergite bands narrowly medianly interrupted (the bands more or less straight); narrow.
Larvae and pupae. The larvae with the thorax broader than the abdomen, and abruptly tapering posteriorly (the prolegs small and weakly developed - an unusual feature among long-tailed forms); tailed. The anal segment abruptly constricted basally into the long, narrow tail; at least as long as the rest of the body (rat-tailed). The larvae scarcely flattened; dark brown, plain; without thoracic hooks; mouth without triangular sclerites; anal segments with lappets. The larvae saprophagous; in decaying vegetation (in peaty moorland pools).
Classification. Subfamily Milesiinae; tribe Sericomyiini.
British representation. 2 species in Britain.
Illustrations. • S. lappona and S. silentis: Verrall. • 15 genera (from Walker). • S. silentis, with assorted other Syrphidae (adult forms).
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’.