Insects of Britain and Ireland: the genera of Syrphidae (hoverflies)
IncludingPyrophaena Schiner; formerly Syrphus p.p.
Adult flies. The flies variously Nomada-like (commonly), or resembling a mining bee, or halictid bee-like, or vespid wasp-like, or sphecid wasp-like (cf. Crossocerus quadrimaculatus), or resembling a wood-wasp (P. granditarsa resembles species of Nomada, Andrena and Sphecodes, and though much smaller is even like Sirex spp. in shape and pattern); black marked with with yellow or grey; minute to medium sized; 5–10 mm long. Wings 4.5–9 mm long.
The head wider than the thorax to about the same width as the thorax. The face entirely dark in ground colour (black); not flat or retreating between antennae and mouth; with a central knob (though this is sometimes only slight); not elongated horizontally into a cone as long as the rest of the head. The frons not inflated; smooth. The eyes bare (at least, none depicted as hairy). Antennae relatively short, drooping; with their bases well separated; black. The third antennal segment ovoid or orbicular. The antennal bristle dorsal; simple (bare).
The humeri bare. The thorax pubescent without stiff bristles interspersed; plain; without longitudinal stripes. The scutellum aeneous (aeneous, according to Walker, Verrall and Coe), or black (? - cf. van Veens key). Wings plain (almost colourless, brown, slightly grey or grey); 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. The lower outer marginal vein markedly diverging from the posterior wing margin to slightly diverging from the posterior wing margin. The upper and lower outer marginal cross veins slightly stepped to strongly stepped. The upper outer marginal cross-vein conspicuously bent near the base the base; not re-entrant. The alula distinct. The front tibiae and/or tarsi dilated in males, broad and flattened in females. The metasternum entire, broad over its whole length.
The abdomen about the same width as the thorax to narrower than the thorax; oval, or ovate, or oblong, or more or less fusiform, or clavate, or linear; with 5–6 segments apparent. The male abdomen with 5 visible segments. The abdomen contrastingly patterned (usually), or not contrastingly patterned. The tergite patterning involving 2, or 2 to 4, or 2 to 5. The colour-patterned tergites marked with yellow, or tawny, or orange, or red (almost), or silvery or greyish. The tergite patterning confined to tergite 3 (P. rosarum only), or not confined to one tergite. The interrupted band on tergite 2 reduced to small paired spots, or not reduced to small spots. The dorsum of tergite 2 exhibiting a wineglass-shaped black area, or without a wineglass-shaped black area. The tergite bands medianly interrupted (all of them, usually), or entire (e.g., in P. granditarsus); narrow (mostly, sometimes occupying the whole of tergites 2–4), or narrow and wide. The spiracles of the third abdominal segment borne in the middle of each side.
Larvae and pupae. The larvae broader posteriorly, tapered to the head; posteriorly blunt and tail-less; scarcely flattened to flattened (sub-rectangular in section); green, or not green; longitudinally striped to not longitudinally striped (the stipe sometimes indistinct); variously coloured, patterned (usually mottled cream and pale brown, usually dorally and laterally longitudinally striped); translucent, or not translucent; dorsally smooth, without projections; mouth with a triangular sclerite on either side; anal segments without lappets. The larvae predatory (some generalized, others aphidiphorous and specializing within that category).
General comments. The front tibiae and tarsi often markedly flattened..
Classification. Subfamily Syrphinae; tribe Bacchini.
British representation. 23 species in Britain.
Illustrations. • P. albimanus: Verrall. • P. clypeatus, P. angustatus: Verrall. • P. granditarsus, P. rosarum (subgenus Pyrophaena): Verrall. • P. ambiguus (subgenus Pachysphaeria): Verrall. • C. illustrata, male (with Merodon and Platycheirus).
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’.