Insects of Britain and Ireland: the genera of Syrphidae (hoverflies)
Adult flies. The flies sphecid wasp-like (cf. Ammophila, Tripoxylon); black, bluish-black, dark or greenish-bronze, with inconspicuously pale abdominal marking; small to medium sized; 9–10.2 mm long. Wings 4.5–8 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. Antennae relatively short, drooping; with their bases approximated; black (or black and brown). The third antennal segment ovoid or orbicular. The antennal bristle dorsal; much longer than the third segment; simple (slightly pubescent).
The humeri bare. The thorax patterned, or plain (sometimes depicted with a pair of anterior pale spots); without longitudinal stripes. The scutellum black; aeneous, or black. Wings plain; with a conspicuous dark stigma; incumbent and almost parallel in repose (slightly grey with a brown stigma, sometimes clouded with brown along the veins). 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 (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 slightly diverging from the posterior wing margin. The upper and lower outer marginal cross veins slightly stepped. The upper outer marginal cross-vein conspicuously bent near the base the base; not re-entrant. The alula rather indistinct.
The abdomen narrower than the thorax; clavate, or linear; proximally petiolated (long and very slender, segments 3 and 4 somewhat widened). The male abdomen with 5 visible segments. The abdomen contrastingly patterned to not contrastingly patterned (mostly rather inconspicuously banded). The tergite patterning involving (when manifest) 2, or 2 to 4. The colour-patterned tergites marked with whitish, or yellow, or silvery or greyish. The tergite bands entire. The spiracles of the third abdominal segment borne in the middle of each side.
Larvae and pupae. The larvae somewhat broader posteriorly, tapered to the head; tail-less, posteriorly with only a short spiracular process; posteriorly blunt and tail-less; scarcely flattened; longitudinally striped; patterned (pale greyish-brownish, with lines of white fat along the dorso-lateral margins, and a pair mid-dorsally one of which extends further forward than the other); dorsally smooth, without projections; mouth with a triangular sclerite on either side; anal segments without lappets. The larvae predatory (associated with ground-layer aphids in shady locations).
Classification. Subfamily Syrphinae; tribe Bacchini.
Illustrations. • Baccha elongata: B. Ent. 737. • Baccha elongata: B. Ent. 737, legend+text. • Baccha elongata: B. Ent. 737, text cont.. • 18 genera (from Walker). • B. elongata, with assorted 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’.