Wednesday, 22 July 2009


I have been fascinated by the transformations of butterflies, moths and dragonflies since childhood; that one body form can be turned into something completely different is amazing. While the changes in butterflies are striking enough, it is those of the dragonflies that I have always found the most interesting. The transition from an aquatic larva to a winged, non-aquatic adult is truly remarkable. In some ways the metamorphosis of a butterfly appears to be a passive process, the larva settling down in a sheltered location to become a pupa from which an adult will ultimately emerge, often many months later. In dragonflies it feels so much more active and immediate, the adult emerging from a larval form that has itself only recently emerged from the water. Of course, this is an illusion in the sense that it is the adult itself, held within its old larval skin, which drags itself from the water to clamber up a suitable stem.

Many of the British dragonfly species (and I include damselflies under this broader title) emerge from mid- to late-morning, which offers the interested observer with the opportunity to witness the breathtaking series of behaviours which deliver the winged adult into the world. A few of the larger species, however, leave the water at dusk, completing their emergence by the early hours. Most individuals select an emergent plant as their place of transformation, clambering up to a position well clear of the water. Once a suitable position has been found, the larva attaches itself head up and then proceeds to swing its body about in a characteristic and jerky manner. It is thought that this behaviour, which also includes various circling leg movements, allows the dragonfly to determine that it is securely attached to its support and also that there are no obstructions close by that might hinder the expansion of its wings. If the wings push up against an obstruction during their expansion phase then they can be severely damaged.

The first stage of the transformation involves a switch from aquatic respiration to aerial respiration. The cuticle then splits and the head, legs and thorax are pulled clear of the larval skin. This appears to be a demanding process because it is invariably followed by a long period during which the insect remains immobile and resting. The abdomen is then withdrawn from the skin and the process of expansion begins, with both the wings and abdomen very slowly increasing in size. Once the process of expansion is complete, the now fully formed adult remains on its support until it is ready to take to the air for its maiden flight, leaving behind the larval skin and all evidence of its once aquatic lifestyle.

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