This big event has been a long time coming. The larva, or nymph, spent between one and two years (though up to five years has been recorded) as a voracious aquatic predator, before finally taking its cues from changes in day length and water temperature.
Unlike maggots and caterpillars, which undergo a single complete rearrangement of internal organs during a chrysalis stage, dragonfly larvae grow continuously via a series of instars. Each one casts off its old tight skin to inflate, then harden, a larger skin underneath. The wing buds also get bigger with each moult. By about the 10th or 12th instar, the larva is fully grown.
In late evening or early morning, the larva hauls itself up an emergent stem, often of a reed, sedge or iris. Tightly gripping an anchor point, the larva starts to redistribute its body fluids, expanding the thorax until its skin splits down the back. Head, shoulders, legs and thorax ease out backwards, then the new dragonfly is dangling by its tail. A pause of an hour gives the legs time to harden – a chemical curing process called sclerotisation.
Clinging to its now empty larval shell, or exuvia, the dragonfly extricates its tail and begins pumping body fluids into its four wings, inflating the fine tracery of the grid-like veins. It will take several more hours until they, and the rest of its body, sclerotise enough for flight.
Did you know?
■ Empty dragonfly larval cases are often complete, except for a single exit hole located behind the head.
■ Newly emerged dragonflies take a few days to develop their full colours, which differ between males and females.