Insects of Britain and Ireland: the genera of Syrphidae (hoverflies)
Adult flies. The flies black; minute to small; 4.5–6 mm long. Wings 4.25–5 mm long (i.e., relatively long-winged).
The head slightly 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 (covered with long, drooping shaggy hairs). The eyes hairy to bare (?). Antennae relatively short, drooping. The third antennal segment ovoid or orbicular. The antennal bristle dorsal; simple.
The humeri hairy, and readily visible behind the head. The thorax pubescent without stiff bristles interspersed; plain; without longitudinal stripes. The scutellum black. Wings plain; without a conspicuously dark stigma; 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 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 near the base the base; not re-entrant. The alula distinct.
The abdomen about the same width as the thorax (in the female), or narrower than the thorax (in the male); narrowly oval (male), or more or less fusiform, or obovate (but somewhat angled a the widest part, in the female); dominated by the large tergites 2 and 3, tergite 4 being minute or not visible; not contrastingly patterned.
Larvae and pupae. The larvae posteriorly blunt and tail-less; flattened (hemispherical); not translucent. The larvae predatory (associated with the galls of an aphid on Artemisia).
General comments. Characterized by the large tergites 2 and 3 in combination with the minute or inconspicuous 4..
Classification. Subfamily Milesiinae; tribe Pipizini.
British representation. 1 species in Britain (T. primus). Widespread in England north to S. Yorkshire.
Illustrations. • Triglyphus primus, female: 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’.