Appearing on Earth even before dinosaurs, dragonflies were among the first winged insects to evolve. Some giant species had a wingspan of almost 75cm but today, with a wingspan of (only!) 10cm, and a body length of nearly 8cm, the Emperor dragonfly, (Anax imperator) is the largest dragonfly in the UK. They may be seen flying around any body of water – small or large, fresh or brackish, as long as the water holds large numbers of aquatic invertebrates to support a dragonfly population.
The female Emperor dragonfly lays eggs on the leaves of vegetation floating on the surface of the water. After about three weeks, the eggs hatch and the emerging nymphs will spend the next year-or-two developing in this aquatic environment.
Both the young, nymphal, stages and the adults are fierce predators.
The water-based nymph has a highly modified lower lip (the labium) which can very rapidly be extended and, with the hooks at the end of the lip, seize its prey (such as other aquatic insects, tadpoles, and even small fish) before retracting it back towards the head and devouring the capture using its strong mandibles. When fully grown, the nymph leaves the water by crawling onto a plant or similar structure. An adult emerges after a final moult.
The adult dragonfly is a highly skilled flyer, and uses its speed and ability to manoeuvre in the air to chase prey; in addition, it has exceptional eyesight due to its large eyes (which are composed of thousands of lenses or ommatidia) offering an almost 360-degree vision allowing rapid detection of movement and accurate navigation.
Captures are held by the spines on its legs and small prey (flies, butterflies, mosquitoes and the like) may be eaten while the dragonfly is still in flight; larger prey, such as other dragonflies, may be consumed when it is at rest.
