Insects of Britain and Ireland: the genera of Syrphidae (hoverflies)
Adult flies. The flies sphecid wasp-like (? - the female having been likened to Crossocerus quadrimaculatus), or cimbicid sawfly-like (a better match for the the narrow-bodied male); black or blackish, with pale marks; small; 7–9 mm long. Wings 4.25–7 mm long.
The head about the same width as the thorax. The face flat or concave in the region between the antennae and the mouth (concave); without a central knob; longitudinally keeled. The eyes bare. Antennae relatively short, drooping; with their bases well separated; black and 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; with longitudinal stripes. The thoracic striping lateral only (greyish or silvery lateral or lateral-anterior stripes only). The scutellum flat, with a well defined edge; black. Wings plain (colourless); 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 gently curved; joining vein R4+5 almost at right angles, so that cell R5 is not extended towards the wing tip; re-entrant to not re-entrant. The alula distinct to indistinct.
The abdomen narrower than the thorax; cylindric,almost linear, or more or less fusiform, or oblong (somewhat waisted in males); contrastingly patterned. The tergite patterning involving 2 and 3, or 2 to 4. The colour-patterned tergites marked with yellow to tawny, or silvery or greyish. The tergite bands medianly interrupted; narrow to wide.
Larvae and pupae. The larvae tapering posteriorly; shortly tailed. The anal segment tapered gradually to the spiracular process. The larvae scarcely flattened (sub-cylindrical, to about 12 mm long); darkish brown, plain; without thoracic hooks; mouth without triangular sclerites; anal segments with lappets. The larvae semi-aquatic to non-aquatic; saprophagous and coprophagous (short-tailed maggots, found in rotting compost, manure, silage, and decaying vegetation, but not under water).
Classification. Subfamily Milesiinae; tribe Xylotini.
British representation. 1 species in Britain (S. pipiens). Throughout the British Isles.
Illustrations. • S. pipiens: Verrall. • 15 genera (from Walker). • S. pipiens, 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’.