Hovering high

Today I read a very interesting paper by David Lack (of fame as an ecologist and evolutionary biologist for his bird studies and his books, of which 'The Life of the Robin' is my favourite). He described his observations on a day of October on top of a high Pyrenean pass. In addition to various flock of migrating birds, he accounts in detail how large numbers of butterflies (mainly Red Admirals and Clouded Yellows) and Common Darter dragonflies (Sympetrum striolatum) steadily crossed the pass towards the Spanish side. That birds migrated had already been well established, but insect migration was then a much more recent, still controversial phenomenon.Lack felt provileged to have witnessed such extraordinary phenomenon, and the feeling was probably enhanced by the beauty of the surrounding mountains, at 2227 m altitude. He wrote "Once in a lifetime perhaps, the ecologist is translated back into a naturalist, through chancing on a spectacle which combines grandeur with novelty. Such was our fortune at the Port de Gavarnie on 13 October 1950."

Cirque du Gavarnie (Photo by Marando-fr, Wikipedia Commons)

Lack's was the first account of hoverflies migrating. In his own words:

Not until we had been at the pass for over an hour did we realize that another insect was migrating, so we do not know whether it was passing from the start. This was a hoverfly, the two collected specimens being males of Episyrphus balteatus. All the other individuals looked the same, and we have no reason to think that any other species was present. The syrphid flies, like the dragonflies, flew steadily forward WSW. against the wind, keeping extremely close to the ground, where the wind was, of course, weaker. Very occasionally one settled for a moment, but otherwise they travelled steadily onward. An estimate of numbers was impossible, but at a guess they were at least twenty times, and perhaps a hundred times, as numerous as the dragonflies. They were the most remarkable migrant of all.

Today there were many E. balteatus in the garden. To think that such tiny, flimsy looking hoverfly, is able of such powerflul climbs and long voyages! It is just plainly amazing.

Episyrphus balteatus on Cat's ear (summer 2006)

A close up. Today, on an ice plant.

Reference
Lack and Lack (1951) Migration of insects and birds through a Pyrenean pass. Journal of Animal Ecology 20:63-67.