Invertebrates
Dragonfly
Anisoptera · also called devil's darning needle, mosquito hawk
A dragonfly is one of the most capable predators alive. It has four wings it can move independently, two eyes that together see almost everything around it, and a hunting method so precise that it catches the insect it is aiming at more than nine times out of ten. And it spent most of its life as a very different animal, lurking underwater.
Overview
Dragonflies are the stout, strong-flying members of the order Odonata, the suborder Anisoptera, with roughly 3,000 species. An adult has a long body, four independently controlled wings, and enormous compound eyes that wrap around the head. It hunts other flying insects on the wing, scooping them into a basket of spiny legs. Dragonflies breed in fresh water on every continent except Antarctica.
The hunter
A dragonfly does not chase — it intercepts, predicting where its prey will be and flying to meet it, correcting all the way. Combined with its flight control, this gives success rates of up to 95 per cent, higher than almost any vertebrate predator.
Two lives
Most of a dragonfly’s life is spent as an aquatic larva, for months or years, hunting tadpoles and insect larvae with a hinged jaw that shoots out from under its head. It then climbs a stem, splits its skin, and emerges as a winged adult that lives only a few weeks.
Harmless to us
Despite names like “devil’s darning needle”, a dragonfly cannot sting or hurt a person. It is, if anything, an ally — the adults eat mosquitoes and midges, and the larvae eat mosquito larvae.
Status
Dragonflies as a group are Not Evaluated. Many are common, but about one in six assessed species is threatened, nearly always through the loss or pollution of wetlands.
Dragonfly: common questions
What is the difference between a dragonfly and a damselfly?
They are the two branches of the order Odonata. A dragonfly, suborder Anisoptera, is usually stout-bodied and a strong flier, holds its wings out flat to the sides when perched, and has large eyes that meet or nearly meet on top of the head, with the hind wings broader at the base than the fore wings. A damselfly, suborder Zygoptera, is slender and a weaker, fluttering flier, folds its wings back along or above the body at rest, and has smaller eyes set clearly apart on the sides of the head, with fore and hind wings of similar shape. As a rough guide, a big robust insect zooming over a pond with wings spread when it lands is a dragonfly; a delicate one drifting through the reeds with wings closed is a damselfly.
How do dragonflies catch their prey?
Adult dragonflies are aerial hunters that intercept flying insects. Rather than chasing a target from behind, a hunting dragonfly tracks the prey with its huge eyes, predicts where it will be a moment later, and flies a path to arrive at that point, making small corrections all the way, a strategy called motion camouflage or predictive interception. It scoops the prey into a basket formed by its bristly legs and either eats it in flight or carries it to a perch. This approach, combined with exceptional flight control, gives dragonflies a hunting success rate far higher than that of most vertebrate predators.
How long does a dragonfly live?
Most of a dragonfly's life is spent underwater as a larva, and that stage lasts from a few months in small warm species to five years or more in large ones in cool water. The winged adult stage, which is what people picture as a dragonfly, is short. After emerging it takes days to a couple of weeks to mature and harden its colours, then it has a reproductive period of perhaps one to several weeks before it dies, worn out or eaten. A very few adults that emerge late and migrate may live a couple of months. So a dragonfly can be years old as an animal but only weeks old as a flying adult.
Are dragonflies good to have around a garden pond?
Yes, on several counts. The adults are efficient predators of midges, mosquitoes, and other small flying insects, and the larvae eat mosquito larvae, other insect larvae, and small invertebrates in the water. A pond that attracts breeding dragonflies is usually a healthy one, because the larvae are sensitive to pollution and low oxygen, so their presence is a good sign. To encourage them, a garden pond should have some open water, a gently sloping edge, submerged and marginal plants for larvae to climb and hunt among, sunny aspect, and no fish, since fish eat the larvae. Dragonflies pose no risk to people, pets, or garden plants.