Insects of Britain and Ireland: the genera of Syrphidae (hoverflies)
Adult flies. The flies muscid-like (cf. Scatophaga species), or pamphiliid sawfly-like (in some cases a better match, cf. Neurotoma); with grey thorax and yellowish-orange or tawny abdomen; small; 6–9 mm long. Wings 6.5–9.25 mm long.
The head about the same width as the thorax to less wide than the thorax. The face without a central knob; produced below and extending beyond the antennae, or not extending below beyond the antennae; not elongated horizontally into a cone as long as the rest of the head. The eyes bare; not rimmed along their facial borders for much of the height of the face. Antennae relatively short, drooping; with their bases well separated (seated on a tubercle); black, or black, ferruginous, and tawny. The third antennal segment ovoid or orbicular. The antennal bristle dorsal; much longer than the third segment; simple (almost bare).
The humeri hairy, and readily visible behind the head. The thorax plain; without longitudinal stripes. Wings plain; incumbent and almost parallel in repose (colourless to slightly grey). 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 bearing 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; not re-entrant. The alula distinct.
The abdomen wider than the thorax; broadly obovate (convex). The male abdomen with 4 visible segments. The abdomen not contrastingly patterned. The spiracles of the third abdominal segment borne at or near the anterior corner of each side.
Larvae and pupae. The larvae tapering anteriorly and posteriorly from the middle; tailed to posteriorly blunt and tail-less; flattened (somewhat dorso-ventrally flattened); brown, plain; with conspicuous lateral projections, or laterally smooth; without thoracic hooks; mouth without triangular sclerites; anal segments with lappets. The larvae semi-aquatic to non-aquatic (able to withstand desiccation); saprophagous; in sap runs and in decaying sap under loose bark (in Fagus, Quercus, Aesculus, Ulmus, Populus, Fraxinus and even Taxus).
General comments. The adults with a concave face leading smoothly to the projecting margin of the mouth.
Classification. Subfamily Milesiinae; tribe Chrysogastrini.
British representation. 4 species in Britain.
Illustrations. • B. bicolor: Verrall. • 18 genera (from Walker).
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’.