British Insects: the Odonata


L. Watson and M. J. Dallwitz

Orthetrum coerulescens (Fabricius, 1798)

Keeled Skimmer Dragonfly.

Adults. Adults about 38–42–46 mm long (the female slightly the shorter). Average wingspan 60 mm; hindwings 28–34 mm long.

The eyes dorsally narrowly apposed to dorsally broadly contiguous; brown (in the female), or blue (in the male).

Legs “very dark”. Thoracic antehumeral stripes present; pale brown (-ish, against the darker brown of the thorax). The wings spread more or less horizontally in repose; dissimilar in shape and venation; sessile; unpatterned and clear (the forewings of the male), or suffused with colour at their bases only (the hindwings of the male), or colour tinted throughout (both fore- and hindwings of the female). The tinting amber. The inner wing venation brown (in the female?), or blackish. Discoidal cell divided longitudinally into a conspicuous triangle and supra-triangle. Antenodal veins in the forewings 10–12 (fewer in the hindwings). Pterostigma well over twice but no more than five times as long as wide; orange (in both sexes).

Abdomen linear from a conspicuously swollen base (in the female), or lanceolate (in the male, but less broadly so than in O. cancellatum); 27–30 mm long; predominantly blue (pruinescent sky-blue to the tip, in mature males), or yellow to brown (in females and immature males); plain (in the male, where it is not darkened over the terminal segments), or predominantly longitudinally lined (that of the female with an uninterrupted narrow median longitudianl band, this briefly crossed by a short, thin transverse band on each of the middle segments); without mid-dorsal spots. The male abdomen without auricles on segment 2; with a single inferior anal appendage.

Nymphs. The nymphs stout, the body expanded in the middle; when mature, 17–23 mm long.

The head in dorsal view not markedly narrowing from immediately behind the eyes. The postocular lobes curving sharply to the back of the head from some distance behind the eyes. The antennae 7 segmented. The mask having the prementum hollowed dorsally. The prementum bearing two long setae inserted near each lateral margin, and two medial fields of 10 to 12 short spiniform setae, the latter flanked by four to seven setae of medium length. The body of the labial palps bearing 3(–5) major setae. Distal margins of the labial palps weakly crenate. Legs longer than the abdomen.

The abdomen terminating in five short spine-like appendages. The cerci no more than hald the length of the paraprocts. The abdomen with mid-dorsal spines. The mid-dorsal abdominal spines prominent on segments 4 to 7. The abdomen without a mid-dorsal spine on segment 8; gizzard with 4–8 folds.

Distribution. Northern Scotland, southern Scotland, northern England, East Anglia, Wales, southeast England, southwest England, Isle of Wight, Ireland, and central southern England (very scarce in the English Midlands and East Anglia). Adults on the wing late may to late September (generally in best mature condition mid-July to mid-August).

Classification. Anisoptera; family Libellulidae.

Illustrations. • Orthetrum coerulescens (from Lucas).

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. British insects: Dragonglies and Damselflies (Odonata). Version: 1st January 2012.’.