Insects of Britain and Ireland: the genera of Syrphidae (hoverflies)
Formerly Xylota p.p.
Adult flies. The flies sphecid wasp-like (cf. Astata boops), or resembling a wood-wasp (in colour-patterning, but much smaller - cf. the wood-wasp Sirex juvencus); black with a blood-red abdominal belt; medium sized; 11–13.5 mm long. Wings 10–12 mm long.
The head about the same width as the thorax. The face flat or concave in the region between the antennae and the mouth; without a central knob; impressed. The eyes not rimmed along their facial borders for much of the height of the face. Antennae relatively short, drooping; with their bases approximated (seated on a tubercle); black. The third antennal segment ovoid or orbicular. The antennal bristle dorsal; much longer than the third segment; simple (basally slightly pubescent).
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; incumbent and almost parallel in repose (pale grey, slightly tinged brown along the veins). 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 to crossing it at or beyond the middle of the adjoining discal cell (near the middle). 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 to slightly 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, or narrower than the thorax; about 6.8–7.4; (sub-) linear. The male abdomen with 4 visible segments. The abdomen not conspicuously furry; contrastingly patterned. The tergite patterning involving 2 and 3. The colour-patterned tergites marked with red (the tail black). The tergite bands partially interrupted and entire (that on tergite 2 only being anteriorly notched); very wide (occupying the whole of tergites 2 and 3). The spiracles of the third abdominal segment borne at or near the anterior corner of each side.
Larvae and pupae. The larvae broader posteriorly, tapered to the head; tailed. The anal segment tapered gradually to the spiracular process. The larvae scarcely flattened; plain; with hooks on the thorax (two red-brown ones lateral to each anterior spiracle); mouth without triangular sclerites; anal segments with lappets. The larvae saprophagous; in rotten wood (especially in the decaying heartwood of live oaks).
General comments. The legs black.
Classification. Subfamily Milesiinae; tribe Xylotini.
British representation. 1 species in Britain (B. lentus).
Illustrations. • B. lentus, male (with Criorhina, Eristalis and Xylota).
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’.