Aeshna isoceles (Green-eyed Hawker/Norfolk Hawker)
This is something of an enigmatic species, at least as regarding names. Originally placed in the Anaciaeshna genus, it was then transferred to the Aeshna genus; there are apparently significant differences between it and other Aeshna species. Allegedly, though, it isn’t really a precise fit for Anaciaeshna either. In 2020 the BDS once again appears to be referring to Anaciaeshna isoceles.
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, 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.
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
- Brown thorax and abdomen with clear wings (contrast with A. grandis)
- Distinctive/diagnostic yellow triangle on dorsal side of S2
- Green eyes (when mature)
| ovipositing |
 |
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’.
Thanks for that, Roy, and well done for managing an u-umlaut [ü]. So. isoceles it is, then, but I won’t tell R.R. 🙂