Insects of Britain and Ireland: the genera of Syrphidae (hoverflies)
Formerly Syrphus p.p.; Conosyrphus, Dendrosyrphus, Syrphella.
Adult flies. The flies Nomada-like, or sphecid wasp-like (cf. D. tricinctus and Nysson spinosus); black with yellow markings; small to medium sized; 9–11.5 mm long. Wings 6.25–10.25 mm long.
The head 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; not elongated horizontally into a cone as long as the rest of the head. The frons not inflated; smooth. The eyes hairy. Antennae relatively short, drooping; with their bases well separated; black and tawny, or black and ferruginous, or tawny. The third antennal segment ovoid or orbicular. The antennal bristle dorsal; simple (bare).
The humeri bare. The thorax patterned, or plain (mostly?); without longitudinal stripes (? - at least, not dorsally striped). The thoracic striping without well defined lateral lines. The scutellum aeneous, or brownish, ferrugineous or tawny. Wings plain (colourless to slightly grey, sometimes slightly tawny, at the base); with a conspicuous dark stigma, or without a conspicuously dark stigma; without black flecks along the hind edges; 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 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 thoracic squamae without long hairs dorsally. The hind legs partly yellow. The anterior anepisternum bare.
The abdomen wider than the thorax to about the same width as the thorax; depressed, oval, or ovate, or oblong. 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. The colour-patterned tergites marked with yellow. The interrupted band on tergite 2 reduced to small paired spots, or not reduced to small spots. The dorsum of tergite 2 without a wineglass-shaped black area. The dorsum of tergite 3 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 partially interrupted, 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 (with conspicuously serrate lateral margins); posteriorly blunt and tail-less; flattened; green (or greenish, e.g. D. tricinctus), or not green; patterned (mottled brown, blackish, greenish, grey and pinkish - bark-like); with dorsal projections; with conspicuous lateral projections; mouth with a triangular sclerite on either side; anal segments with a pair of curved, horn-like projections; anal segments without lappets. The larvae predatory (D. tricinctus on tenthredinid sawfly and noctuid moth larvae, others on arboreal aphids of conifers and hardwood trees).
General comments. The adults rendered conspicuous by unusual patterns of abdominal markings - curves, hooks, etc., distinguished by the pair of long, backwardly pointing horn-like projections from the blunt anal segment.
Classification. Subfamily Syrphinae; tribe Syrphini.
British representation. 5 species in Britain.
Illustrations. • D. albostriatus, D. pinastri, D. tricinctus and D. venustus: Verrall.
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’.