Insects of Britain and Ireland: the genera of Syrphidae (hoverflies)
Adult flies. The flies vespid wasp-like (cf. Dolichovespula and Vespula), or Nomada-like, or resembling Colletes (S. pyrastri only); black with yellow markings, the thorax dusted greenish black; small to medium sized; 8–11(–13) mm long. Wings 7.25–11.5 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 (never with a black facial stripe, though the mouth edge is sometimes black); not flat or retreating between antennae and mouth; with a central knob; not elongated horizontally into a cone as long as the rest of the head. The frons not inflated; smooth. The eyes hairy, or bare. Antennae relatively short, drooping; with their bases well separated; black, ferruginous, and tawny. The third antennal segment ovoid or orbicular. The antennal bristle dorsal; about as long as the third segment, or much longer than the third segment; simple (bare).
The humeri bare. The thorax pubescent without stiff bristles interspersed; plain; without longitudinal stripes. The scutellum at least partly yellow, or aeneous, or brownish, ferrugineous or tawny. Wings plain (more or less colourless); with a conspicuous dark stigma (sometimes), or without a conspicuously dark stigma; without black flecks along the hind edges; 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. 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 and lower outer marginal cross veins more or less continuous. The upper outer marginal cross-vein gently curved; not re-entrant. The alula distinct. The thoracic squamae with long hairs on their dorsal surfaces (this supposedly being diagnostic for the genus). The anterior anepisternum bare.
The abdomen wider than the thorax to about the same width as the thorax; depressed, oval, or obovate. The lateral margins of the tergites exhibiting beaded rims. The abdomen with 5–6 segments apparent. The male abdomen with 5 visible segments. The abdomen contrastingly patterned. The tergite patterning involving 2 to 4, or 2 to 5. The colour-patterned tergites marked with yellow. The dorsum of tergite 2 exhibiting a wineglass-shaped black area, or without a wineglass-shaped black area. The dorsum of tergite 3 with a sunglasses-shaped pale partially-interrupted pale band, or with a brassiere-shaped pale partially-interrupted band, or with neither a sunglasses-shaped nor a brassiere-shaped partially-interrupted pale band. The tergite bands medianly interrupted, or medianly interrupted and entire, or medianly interrupted, partially interrupted, and entire (the one on tergite 2 interrupted, others variously interrupted or only partially so or entire); narrow. 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; green, or not green; longitudinally striped to not longitudinally striped; greenish to pale brownish, patterned (with white, red and yellow or brown chevrons); translucent; mouth with a triangular sclerite on either side; anal segments without lappets. The larvae predatory (on divers arboreal and ground layer aphids).
Classification. Subfamily Syrphinae; tribe Syrphini.
British representation. 3 species in Britain.
Illustrations. • S. ribesii, female (with Scaeva, Helophilus and Xanthogramma). • S. ribesii and S. torvus, Epistrophe grossulariae and Melangyna barbifrons (thoracic squamae).
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’.