British Insects: the Odonata
Adults. Adults about 73–78–82 mm long (the males somewhat the longer). Average wingspan 106 mm; hindwings 45–51 mm long.
The eyes dorsally broadly contiguous, or dorsally narrowly apposed to dorsally broadly contiguous (in the female?); brown and green, or green.
Legs brownish black and yellow (the undersides of the fore-femora yellow). Thoracic antehumeral stripes absent. The wings spread more or less horizontally in repose; dissimilar in shape and venation; sessile; unpatterned and clear. The inner wing venation blackish. Discoidal cell divided longitudinally into a conspicuous triangle and supra-triangle. Antenodal veins in the forewings about 16–20 (fewer in the hindwings); incorporating two conspicuously stronger primaries, and those in the costal and subcostal spaces unaligned. Pterostigma narrow-linear; black, or dark brown.
Abdomen linear from a conspicuously swollen base (briefly constricted behind the swelling in the male); 49–51 mm long (female), or 53–61 mm long (male); predominantly blue (male), or green (female); predominantly longitudinally lined (with a continuous, median black line which is crossed by a short band on each segment of the male, and on the anterior segments in the female); 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, 45–56 mm long.
The eyes large; approaching one another closely at a point on the top of the head; markedly flattened dorsally, their posteror margins forming a transverse straight line in dorsal view (this and the more rounded outline of the head readily distinguishing this species from the Aeschnas). The head in dorsal view not markedly narrowing from immediately behind the eyes. The postocular lobes curving smoothly to the back of the head from immediately behind the eyes. The antennae 7 segmented. The mask narrowed gradually to the hinge; with a flat prementum; with a short slit-like median cleft. 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. Northern England, English Midlands, East Anglia, Wales, southeast England, southwest England, Isle of Wight, and central southern England (mainly restricted to the southern counties of Britain). Adults on the wing late may to early September (generally in best mature condition mid-June to early August).
Classification. Anisoptera; family Aeshnidae.
Illustrations. • Anax imperator (from Lucas). • Anax imperator: nymph (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. http://delta-intkey.com’.