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

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L. Watson and M. J. Dallwitz

Triglyphus Loew

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.

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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.’.