Insects of Britain and Ireland: the genera of Syrphidae (hoverflies)
Adult flies. The flies Nomada-like; black with tawny marking; small to medium sized; 9–11 mm long. Wings 5.5–8.25 mm long.
The head slightly wider than the thorax to about the same width as the thorax. The face flat or concave in the region between the antennae and the mouth (concave); without a central knob; longitudinally keeled. The eyes bare. Antennae relatively short, drooping; with their bases approximated (inserted in a small cavity in a protuberance in the middle of the face); black and ferruginous. 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; without longitudinal stripes. The scutellum flat, with a well defined edge; black. Wings plain (slightly grey); without a conspicuously dark stigma; incumbent and almost parallel in repose (and somewhat deflexed). Wing veins R2+3 and R4+5 not forming a closed cell. The anterior cross vein R-M in cell R5 crossing it at or beyond 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 hind femur with a large triangular plate at its distal end.
The abdomen about the same width as the thorax; rather narrowly obovate (in the male), or oval (in the female); contrastingly patterned. The tergite patterning involving 2 and 3. The colour-patterned tergites marked with tawny. The dorsum of tergite 2 exhibiting a wineglass-shaped black area, or without a wineglass-shaped black area. The tergite bands broadly medianly interrupted; narrow (in the female), or wide (in the male).
Larvae and pupae. The larvae tapering posteriorly; shortly tailed. The anal segment tapered gradually to the spiracular process. The larvae scarcely flattened to flattened (up to 15 mm long, oval in section, with small prolegs); plain; with hooks on the thorax (a row of mostly small ones on the anterior margin of the mesothorax, and a few more dorsal and on the lateral thoracic margins); mouth without triangular sclerites; anal segments with lappets. The larvae saprophagous; probably short-tailed maggots, to be found in decaying vegetation (at the margins of ponds and ditches).
General comments. The median black abdominal component in the male forms a conspicuous pattern - see illustration. Differing from Xylota in the swollen hind femur with its distal protuberance.
Classification. Subfamily Milesiinae; tribe Xylotini.
British representation. 1 species in Britain (T. scita). Fens and marshes of southern and eastern England, extending coastally to southern Scotland, and also recorded from Ireland.
Illustrations. • Tropidia scita (British Tropidia Hover-fly: B. Ent. 401). • Tropidia scita: B. Ent. 401, legend+text. • Tropidia scita: B. Ent. 401, text cont.. • T. scita: Verrall. • 15 genera (from Walker). • T. scita, 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’.