British Insects: the Odonata


L. Watson and M. J. Dallwitz

Aeshna isosceles (Müller, 1767)

Norfolk Hawker Dragonfly.

Adults. Adults about 62–67–72 mm long. Average wingspan 93 mm; hindwings 39–45 mm long.

The eyes dorsally broadly contiguous; predominantly green.

Legs black and brown (the femoral bases brown). Thoracic antehumeral stripes absent. The wings spread more or less horizontally in repose; dissimilar in shape and venation; sessile; unpatterned and clear (the forewings), or suffused with colour at their bases only (the hindwings). The tinting amber. The inner wing venation blackish. Discoidal cell divided longitudinally into a conspicuous triangle and supra-triangle. Antenodal veins in the forewings about 18–22 (fewer in the hindwings); incorporating two conspicuously stronger primaries, and those in the costal and subcostal spaces unaligned. 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; light brown.

Abdomen linear from a conspicuously swollen base (briefly somewhat constricted behind the swelling in the male); 49–54 mm long (female), or 47–50 mm long (male); predominantly light brown; plain (save for the pale yellow median triangle on segment 2 in both sexes); with a conspicuous, median yellow triangle on segment 2; without mid-dorsal spots. Abdominal segments 9 and 10 neither colour-banded nor colour-spotted. The male abdomen auriculate on segment 2; with a single inferior anal appendage.

Nymphs. The nymphs stout, the body expanded in the middle; when mature, 38–44 mm long.

The eyes large; approaching one another closely at a point on the top of the head; convex dorsally, their posterior margins not aligned. 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 shortly abruptly narrowed well before the hinge, with the prementum stalked to narrowed gradually to the hinge (?). The prementum relatively short, being much less than twice as long as its front width. The mask with a flat prementum; with a short slit-like median cleft. The prementum bearing 0 major setae. The body of the labial palps bearing 0 major setae. Legs shorter than the abdomen; fore- and middle tarsi 3-segmented.

The abdomen terminating in five short spine-like appendages; gizzard with 4–8 folds.

Distribution. East Anglia (restricted to the Norfolk Broads). Adults on the wing late may to early July (generally in best mature condition mid- to late June).

Classification. Anisoptera; family Aeshnidae.

Illustrations. • Aeshna isosceles (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.’.