Monday, November 28, 2011

Come Fly With Me

Migrant Hawker, Aeshna mixta
The Migrant Hawker dragonfly (Aeshna mixta) is a relatively new addition to the odonate fauna of Ireland, with the first sighting being reported in 2000 (1). However, this was during the DragonflyIreland survey of dragonflies and damselflies and it may have been present before this. It has the latest emergence of all dragonflies in Ireland, appearing in in the south and south-east of the country in late July and present till late October. Its flight is quite impressive to behold:- hovering around low-lying vegetation, it can quickly shoot high into nearby treetops with ease. Studies of the flight in Aeshna spp. using both tethered animals and model wings have revealed it to be a very complex process (2). It was seen that Aeshna spp. fly by using unsteady aerodynamic mechanisms to generate leading edge vortices or high lift when needed and that the dragonfly controls the flow mainly by changing the angle of attack of the wings. Unsteady aerodynamics refers to the effects on flight that changes in the air flow or in the position or orientation of a body (in this case a wing).
Migrant Hawker, Aeshna mixta
  1. Nelson and Thompson 2004. The Natural History of Ireland's Dragonflies pp. 193-199
  2. Wang and Sun, 2005. The Journal of Experimental Biology 208 pp. 3785-3804

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