Insects of Britain and Ireland: the genera of Syrphidae (hoverflies)

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L. Watson and M. J. Dallwitz

Didea Macquart

Formerly Syrphus p.p.

Adult flies. The flies Nomada-like; black to blue-black, marked with yellow to greenish or bluish; medium sized; 11–14.5 mm long. Wings 7–11.5 mm long.

The head wider than the thorax. The face ground-coloured at least part yellow; not flat or retreating between antennae and mouth. The frons not inflated; smooth. The eyes bare. Antennae relatively short, drooping; with their bases well separated. The antennal bristle dorsal; simple (bare).

The humeri bare. The thorax pubescent without stiff bristles interspersed; plain; without longitudinal stripes. The scutellum at least partly yellow, or brownish, ferrugineous or tawny (dull tawny in D. alneti). Wings relatively plain (slightly grey, brownish basally and along the costa); with a conspicuous 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 with 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 slightly 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 anterior anepisternum bare.

The abdomen much wider than the thorax; depressed, oval, or ovate to 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, or whitish and yellow, or yellow and silvery or greyish. 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 and partially interrupted (the first interrupted, the others entire and in the form of bands shaped like skiing-glasses); narrow to wide; sometimes complexly figured. The spiracles of the third abdominal segment borne in the middle of each side.

Larvae and pupae. The larvae only slightly tapering anteriorly and posteriorly from the middle; posteriorly blunt and tail-less; up to 12 mm long, flattened (with conspicuously serrate lateral margins and mid-dorsal projections); patterned (mottled brown and black, like bark); with dorsal projections; with conspicuous lateral projections; mouth with a triangular sclerite on either side; anal segments without lappets. The larvae predatory (aphidivorous, mostly on conifers but also recorded from Salix).

Classification. Subfamily Syrphinae; tribe Syrphini.

British representation. 3 species in Britain.

Illustrations. • D. alneti and D. fasciata (Verrall). • D. intermedia (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.’.