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

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L. Watson and M. J. Dallwitz

Melanostoma Schiner

Formerly Syrphus p.p.

Adult flies. The flies variously somewhat cephid sawfly-like, or sphecid wasp-like (cf. Crossocerus quadrimaculatus); black to dark bronze or greenish bronze, with pale abdominal markings; minute to small; 4–6 mm long (M. dubium), or 5–7 mm long (M. mellinum), or 8–9 mm long (M. scalare). Wings 4.75–8 mm long.

The head slightly wider than the thorax to about the same width as the thorax. The face entirely dark in ground colour (black); not flat or retreating between antennae and mouth; not elongated horizontally into a cone as long as the rest of the head. The frons not inflated; smooth. The eyes hairy, or bare (?). Antennae relatively short, drooping; with their bases well separated; black and ferruginous, or black, or tawny. The third antennal segment ovoid or orbicular. The antennal bristle dorsal; simple (bare).

The humeri bare. The thorax pubescent without stiff bristles interspersed; plain. The scutellum black (cf. van Veen’s key; brassy or golden-green according to Coe’s). Wings plain (pale grey, with black 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. The lower outer marginal vein markedly diverging from the posterior wing margin. The upper and lower outer marginal cross veins slightly stepped. The upper outer marginal cross-vein basally conspicuously bent near the base the base; not re-entrant. The alula distinct. The front tibiae and/or tarsi simple. The metasternum reduced, the sclerotized part small with the central area diamond-shaped.

The abdomen narrower than the thorax (in the males), or about the same width as the thorax to narrower than the thorax (in the females); oval, or oblong, or clavate, or linear, or more or less fusiform (much narrower in males); with 5–6 segments apparent. The male abdomen with 5 visible segments. The abdomen contrastingly patterned, or not contrastingly patterned (when melanic). The tergite patterning involving (when present) 2, 3, and 4, or 2, 3, 4, and 5. The colour-patterned tergites marked with yellow, or tawny. The tergite patterning not confined to one tergite. The interrupted band on tergite 2 reduced to small paired spots. The tergite bands medianly interrupted; narrow to wide. The spiracles of the third abdominal segment borne in the middle of each side.

Larvae and pupae. The larvae broader posteriorly, tapered to the head; posteriorly blunt and tail-less; scarcely flattened; green; shining translucent, patterned (with dark spots), or plain (?); translucent; mouth with a triangular sclerite on either side; anal segments without lappets. The larvae predatory (probably aphidivorous).

General comments. Differs from Platycheirus in having the front tibiae and tarsi cylindrical.

Classification. Subfamily Syrphinae; tribe Bacchini.

British representation. 3 species in Britain.

Illustrations. • M. mellinum and M. scalare: Verrall. • M. scalare, 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.’.