Photo 1. The emperor dragonfly (Anax imperator) is one of Croatia’s largest dragonflies. (Photo by Nina Trinajstić)
Dragonflies, insects of the order Odonata (meaning “toothed-ones”), appeared on Earth several hundred million years ago, much earlier than the time when dinosaurs walked the Earth, and since then they have not changed much. They have two pairs of wings. The wings of the robust dragonflies (Anisoptera) are not equal in size – the hind set of wings is somewhat larger than the front set, enabling them to fly faster – and are held flat and away from the body when the dragonfly is resting. The wings of the smaller and more delicate damselflies (Zygoptera) are equal in size and are held upright when resting. Interestingly, in flight, each set of wings operates separately, allowing dragonflies to fly in all directions, even backwards or to hover in one spot, making them fast and agile fliers.
Being the fastest fliers in the world of insects, dragonflies need to have very good eyesight. A dragonfly’s compound eyes, covering most of its head like a helmet, consist of several thousand tiny polygonal eyes that resemble honeycomb. With these eyes, a dragonfly can simultaneously see on all sides and can spot prey as far away as 40 metres! Given the dragonfly’s combination of motion sensitive eyes and remarkable flying ability, its prey rarely gets away. Its legs are also adapted to hunting and assist in grabbing or holding prey, which it can eat while flying, using its powerful, toothed jaws.
As its lifecycle consists of an adult stage and larva stage in water, the places where we are most likely to find the dragonfly are near stationary waters such as lakes, marshes and ponds, but also near flowing waters such as streams and rivers. Dragonfly larvae spend the whole stage underwater, hiding on the bottom and hunting. They are very predatory and voracious, feeding on insects, tadpoles and even small fishes! The dragonfly remains in its larva form for up to four years, and when the time comes, it emerges from the water and fastens on to a nearby plant or rock and moults for the last time. The larva’s skin opens on its back and a young dragonfly emerges through the opening, first its head and thorax with legs, and then its abdomen. Initially, its wings are wrinkled, but spread fairly quickly, and when they are dry and firm, the young predator flies away, ready to hunt.
As organisms, dragonflies are the perfect indicators of environmental pollution (bio-indicators) because some of the pollutants permanently present in the environment become concentrated in their bodies. Dragonflies also help to keep the number of mosquitoes and other small insects under control. Their presence signifies the quality and high level of conservation of the ecosystem in which they live.