Insects of Britain and Ireland: the genera of Syrphidae (hoverflies)
Adult flies. The flies sphecid wasp-like (cf. Stigmus solskyi and Crossocerus spp.); blackish, often marked yellowish or tawny; minute to small; 3–6 mm long. Wings 3–5.5 mm long.
The head wider than the thorax to about the same width as the thorax. The face entirely dark in ground colour; flat or concave in the region between the antennae and the mouth; without a central knob; produced below and extending beyond the antennae, or not extending below beyond the antennae. Antennae relatively short, drooping; with their bases approximated, or with their bases well separated; black, or black and red. The third antennal segment ovoid or orbicular. The antennal bristle dorsal; simple (bare).
The humeri hairy, and readily visible behind the head. The thorax plain. The scutellum black. Wings patterned to plain (slightly grey, with (e.g., N. podagrica) or without (e.g., N. tenur) a brown band from mid-costa to the disc and brown clouding of apical transverse veins); 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. Vein R without bristles. The lower outer marginal vein markedly diverging from the posterior wing margin. The upper and lower outer marginal cross veins strongly stepped. The upper outer marginal cross-vein conspicuously bent well above the base; bent at a sharp angle to curved on the bend; joining vein R4+5 almost at right angles, so that cell R5 is not extended towards the wing tip; not re-entrant. The alula indistinct.
The abdomen wider than the thorax to narrower than the thorax (wider in the females); clavate (heavily so in females); proximally petiolated (more or less so, in females), or not petiolated. The male abdomen with 4 visible segments. The abdomen contrastingly patterned (but sometimes colour-tailed only). The tergite patterning involving 2 and 3. The colour-patterned tergites marked with yellow, or tawny. The interrupted band on tergite 2 reduced to small paired spots, or not reduced to small spots. The tergite bands medianly interrupted, or entire, or medianly interrupted and entire, or partially interrupted and entire; narrow. The spiracles of the third abdominal segment borne at or near the anterior corner of each side.
Larvae and pupae. The larvae to about 6 mm long, tapering posteriorly; tailed. The anal segment tapered gradually to the spiracular process; shorter than the rest of the body (not rat-tailed). The larvae dorso-ventrally flattened (with small prolegs); brown, plain; with hooks on the thorax (a single pair oat the anterior margin of the prothorax, directed backwards), or without thoracic hooks; mouth without triangular sclerites; anal segments with lappets. The larvae aquatic to non-aquatic; saprophagous, or coprophagous (found in decaying vegetation around ponds and in farmyard manure), or phytophagous (? - being also recorded from Petasites petioles).
General comments. The adults with a concave face leading smoothly to the projecting margin of the mouth, and a thickened hind femur.
Classification. Subfamily Milesiinae; tribe Chrysogastrini.
British representation. 6 species in Britain.
Illustrations. • N. dispar, N. podagrica: Verrall. • 18 genera (from Walker). • N. podagrica, with assorted other 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’.