British Insects: the Odonata


L. Watson and M. J. Dallwitz

Ischnura elegans (van der Linden, 1820)

Blue-tailed Damselfly.

Adults. Adults about 27–31–35 mm long. Average wingspan 35 mm; hindwings 14–20 mm long.

The eyes lateral and widely separated; black and blue, or green and blue (usually dark, with a circular blue (rarely yellowish or greenish) spot at the rear, in both sexes). The front of the head immediately interior to the eyes pale whitish blue.

Legs black and blue ((-ish) below). Hind tibia without a featherlike expansion. Thoracic antehumeral stripes present (usually, humeral stripes also visible), or absent (in varieties with a rose-pink or brown thorax); blue, or violet, or green (-ish). The wings held vertically in repose; similar in shape and venation; petiolate; unpatterned and clear. The inner wing venation blackish. Discoidal cell a simple quadrilateral, not longitudinally divided (trapezoid, without transverse veinlets). The wings exhibiting 3 postquadrilateral cells between the quadrilateral cell and the subnodus. Antenodal veins in the forewings 2. Pterostigma elongated but only about about twice as long as wide to well over twice but no more than five times as long as wide (teardrop-shaped, the same size and shape in forewings and hindwings of both sexes); black and yellow, or pale with a dark centre (yellow, or yellow and black to dark blue internally in forewings and hindwings of the male only?). The hindwings with only one row of cells distal to the pterostigma between the costa and the radial vein.

Abdomen linear from base to tip, or linear from base to tip to linear from a conspicuously swollen base (slender); 22–29 mm long; predominantly black (marked with narrow intersegmental yellow bands, and posteriorly with blue or brown); predominantly transversely banded (generally both sexes with thin yellow intersegmental bands, and with segment 8 light blue or rarely brown); without mid-dorsal spots. The male abdomen without auricles on segment 2; with paired inferior anal appendages. Abdominal segment 8 of the female with a ventral apical spine (this small).

Nymphs. The nymphs elongate and slender-bodied, gradually tapering posteriorly; when mature, 21.5–25 mm long.

The head in dorsal view 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 with the scape considerably shorter than the other segments taken together; with the first flagellar segment longer than the pedicel. The mask narrowed gradually to the hinge; without a median cleft. The prementum bearing 8–11 major setae (4+4 to 6+5). The body of the labial palps bearing 6–7 major setae. The outer margins of the labial palps without spines. Distal margins of the labial palps crenate and coarsely toothed. The moveable hooks of the labial palps without setae. The apical combs of the tibiae mainly of trifurcated setae.

The abdomen terminating in three conspicuous caudal gills. The three caudal appendages all lamellar. The caudal lamellae oval; pointed; hyaline without coloured markings; with one margin hairless beyond the middle, the other hairy to nearer the apex (according to Gardner’s key to the genus, but his Fig. 10f contradicts this); nodate, with the marginal hairs coarser proximally to the node and finer beyond it; with much-branched primary tracheal branches leaving the main trunk at an upward angle. The gizzard with 8–16 radially symmetrical folds.

Distribution. Northern Scotland, southern Scotland, northern England, English Midlands, East Anglia, Wales, southeast England, southwest England, Isle of Wight, Ireland, and central southern England (widespread and generally common, but scarcer at higher elevations). Adults on the wing late April to early October (generally in best mature condition late May to late August).

Classification. Zygoptera; family Coenagriidae.

Illustrations. • Ischnura pumilio and I. elegans (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.’.