Colour variation in the Southern Hawker Dragonfly


Dragonflies and damselflies emerge from their larval skins in an immature state and necessarily spend some time away from  water, avoiding contact with others of their own kind while their wings and external skeleton harden and their adult colours gradually develop.  The immature males of many species pass through a distinct juvenile phase during which they resemble females until their true colours as adult males  become apparent.

The Southern Hawker (Aeshna cyanea) is a large dragonfly which is quite common in our area. It may be familiar even to urban dwellers as it will visit quite small garden ponds. The species is readily identified by the conspicuous pair of large oval spots on top of the thorax (behind the eyes) and by the bands of colour across the tail end of the abdomen (whereas similar species have paired spots there).  According to W.J. Lucas (British Dragonflies, London 1900):  “At first the ground-colour is rather light brown, and the spots are yellow.  The latter change through green to blue, while the former becomes darker. The pterostigma is at first yellow.” (The pterostigma is the spot close to the outer end of the leading edge of each wing.)  In females the colouration of the abdominal spots normally stabilises as yellowish-green (although a blue form occurs very rarely).  The typical appearance of a mature male can be seen in the photograph below.

A mature male Southern Hawker; The Mythe, 8 August 2007

Recently I noticed a hawker which looked almost ghostly as it flew above me in the shade of a tree.  When it settled I was able to photograph it  and the image below shows that it was clearly an immature male Southern Hawker.  However, rather than the greenish tint I would have expected to see in the abdominal spotting, this specimen was displaying a powder blue colour.  It would be interesting to know if I have captured a temporary phase in the development of this individual or whether it is destined to be an exceptionally blue adult when fully mature.

An immature male Southern Hawker; The Mythe 20 July 2018

 

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