Isoaeschna isoceles (Green-eyed Hawker/Norfolk Hawker)

This has been something of an enigmatic species, at least as regarding names. Over history it has been placed variously in the Anaciaeschna genus and in the Aeshna genus. There are apparently significant differences between it and other Aeshna species, though, it really wasn’t a precise fit for Anaciaeschna either. In 2020 the BDS once again appeared to be referring to Anaciaeschna isoceles but in 2024 seems to have reverted to Aeshna isoceles. In August 2023 it was ascribed to a new genus of Isoaeschna.

Confusion continues to the species name which is variously written as A. isosceles [R. R. Askew, 1987] and subsequently A. isoceles [Dijkstra/Lewington and JP Boudot et al]. Personal opinion: since it is named for the distinctive isosceles triangle on the top of abdominal segment 2, one might think that A. isosceles might be more appropriate and that some later, otherwise revered, fellow couldn’t spell. So I tend to side with R. R. Askew. Despite personal opinion, though, the registered name and all modern texts seem to use isoceles so that’s what I’ve used here.

The enigma continues to the vernacular name where, in the UK, it has traditionally been termed Norfolk Hawker because its range was originally restricted to Norfolk. However, it’s breeding range has now spread to include Suffolk, Cambridgeshire, Hertfordshire, Essex, Kent, and continues to expand so to tag it Norfolk now seems inappropriate to some. Green-eyed Hawker, the name suggested by Dijkstra/Lewington, which has always been more appropriate in a European context, also now seems more appropriate in the UK, IMHO. However, traditions die hard and there are factions that fiercely cling on to Norfolk Hawker as the common name.

[See my article, Triangle of Confusion, discussing these naming issues.]

Whatever we call it, It is a delightful dragonfly and we made a trip up to the Norfolk Broads in search of it, managing to find a good selection. They may be tagged as rare but they seemed locally abundant.

Id Notes

  • Tan/Brown thorax and abdomen with clear wings (contrast with A. grandis)
  • Distinctive/diagnostic yellow triangle on dorsal side of S2
  • Green eyes (when mature)
in flight
3 comments on “Isoaeschna isoceles (Green-eyed Hawker/Norfolk Hawker)
  1. Roy Woodward says:

    I believe that the “otherwise revered fellow” who couldn’t spell was Otto Friedrich Müller – who published the original scientific name/description of the species in 1767.
    This makes ‘isoceles’ the correct spelling in the species name, even though it was no doubt intended to be ‘isoSceles’.

    • JC says:

      Thanks for that, Roy, and well done for managing a u-umlaut [ü]. So. isoceles it is, then, but I won’t tell R.R. 🙂

      • Leopold says:

        Today we found this dragonfly in Wales just hatching from its crysalis, with a head as big as my wife’s thumb, that an app has identified as “Aeshna isoceles”.. however its freshly emerged body is bright green, it does have clear wings, and its eyes are black. I wish I could fwd a photo, and that we’d placed a coin or something to indicate scale.

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