Dragonfly exuviae

Posted: Tuesday 26 August 2014
by Richard Jones

The rattling whirr of dragonfly wings around a large pond is an awe-inspiring sound, especially in their hundreds.

The rattling whirr of dragonfly wings around a large pond is an awe-inspiring sound, especially in their hundreds. On a good day hundreds of the insects, perhaps a dozen species if damsels are included, range far out across the water.

They also wander far from their breeding places and the large hawkers (Aeshna and Anax species) will commonly visit woodland edges and hedgerows (including gardens) several kilometres from the nearest pond, patrolling up and down after flying prey.

They sometimes visit patently non-breeding water sites. One of my fondest memories is the small outdoor swimming pool at La Pacifica eco-ranch in Costa Rica, where after a steamy day in the mosquito-infested jungle we could relax in the refreshingly unheated water, safe in the knowledge that the squadron of 1,000 darters and hawkers zooming above our heads was keeping the airspace vampire-free. Of course they weren't breeding in this artificial water source, as demonstrated by the lack of exuviae.

These are the final moulted skins of the aquatic nymphs, which are left high and dry, attached to the emergent vegetation or surrounding stones. After the full-grown nymph hauls out of the water the adult dragon or damsel exits through a split down the back, inflates and dries its wings, and finally flies off.

In the flurry of a busy pond it's often difficult to know just how many dragonflies are about. With comings and goings from nearby pools it soon becomes impossible to have any clear idea of individual species population numbers. It is here that exuviae counting becomes important. The skins can be tagged, collected, counted and monitored, and since one skin means one dragonfly, there are no muddles or duplications. They can usually be identified to species, and often to sex. When I saw a female broad-bodied chaser (Libellula depressa) by my tiny ornamental pond I could be sure it had genuinely bred there, since the fresh exuviae was in evidence below. For some reason I never saw a common blue damselfly (Enallagma cyanthigerum) there, but was able to count several dozens of their ghostly remains crawled up along the pleated edges of the butyl liner.

Incidentally, it's an odd quirk of scientific jargon that exuviae, the plural form of the word, is always used even for one individual skin. Perhaps it's a bit like taking your clothes off; slipping out from a rainbow unicorn onesie is still not taking off a 'clothe'.

Dragonflies and damselflies are astonishing and beautiful beasts, and it's sometimes hard to remember that they live most of their lives as ungainly aquatic gargoyles. The striking zombie-like shells they leave, as they turn from larval monster to adult fairy, are conspicuous reminders of their secret lives in the primordial murk of the typical garden pond.

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