Invertebrates
Common Green Darner
Anax junius · also called green darner, darning needle, mosquito hawk
The common green darner is one of North America’s largest and most familiar dragonflies — a fast, bright-green-and-blue insect that hawks for mosquitoes over ponds and meadows. It is also a genuine migrant, crossing the continent in a multi-generation relay that echoes the monarch butterfly’s.
Overview
Green darners breed in still and slow fresh water — ponds, marshes, ditches, lake edges — across North and Central America, and the adults range far from water to feed, turning up over fields, gardens, forest clearings, and city parks. They are among the first dragonflies seen in spring and among the last in autumn, because part of the population overwinters far to the south and returns north early.
A flying predator
The dragonfly body is built entirely around aerial hunting:
- Eyes that wrap around most of the head, each with tens of thousands of lenses, giving near-total visual coverage and sharp motion detection.
- Four wings driven independently, allowing hovering, instant direction changes, backward flight, and bursts of speed.
- Legs held in a basket in front of the body to scoop prey out of the air, which the dragonfly then eats on the wing or from a perch.
Green darners hunt by interception — computing a course to where the prey will be — and catch their target in the great majority of attempts, one of the best success rates of any hunting animal.
The underwater life
Most of a green darner’s existence is spent as an aquatic nymph. The nymph is a drab, sturdy, predatory creature that stalks the pond bottom and ambushes tadpoles, insect larvae, small fish, and other nymphs, seizing them with a hinged lower jaw that shoots forward like a harpoon. When ready, the nymph climbs a plant stem out of the water, its skin splits, and the winged adult hauls itself out and expands its wings.
Migration
The green darner is one of a handful of dragonflies that undertake long-distance seasonal migration. Research combining citizen-science sightings with chemical signatures preserved in the wings has shown a three-generation cycle: a generation flies south in late summer and breeds in the southern US and Mexico; their offspring develop over winter without migrating; and a spring generation flies back north to start the year’s breeding again. Green darners often travel in large mixed swarms with other dragonfly species, sometimes alongside migrating hawks that prey on them.
Status
The common green darner is Least Concern, abundant, and adaptable, using a wide range of wetland types including artificial ponds. Like all freshwater insects it depends on unpolluted water for its larvae, and the draining and contamination of wetlands is the main threat to local populations. As a heavy consumer of mosquitoes and midges at every life stage, it is a valuable part of wetland ecosystems.
Common Green Darner: common questions
Do dragonflies migrate like monarch butterflies?
The common green darner does, and it works the same relay way. A generation that emerges in the northern US and Canada in summer flies south in autumn, some reaching Mexico, and breeds there. Their offspring, a non-migratory generation, develop over winter in the south. A third generation then flies north in spring to recolonise the breeding range, arriving as the first darners of the year. No individual makes the full round trip — it takes about three generations and roughly 900 kilometres each way, tracked using isotopes locked into the insects' wings.
How good a hunter is a dragonfly?
Exceptional. Green darners and other dragonflies catch prey in flight by intercepting it — predicting where the target is heading and flying to meet it, rather than simply chasing — and they succeed in roughly 90–95% of attempts, a hit rate higher than lions, sharks, or birds of prey. Their huge wraparound eyes, independently controllable wings, and a specialised set of nerve cells for tracking moving targets make this possible.
Can dragonflies sting or hurt you?
No. Dragonflies have no sting, and although a very large one can pinch with its jaws if held, it cannot break human skin in most cases and is completely harmless. Old folk names like "devil's darning needle" and "horse stinger" reflect superstition, not biology. Dragonflies are beneficial, eating large numbers of mosquitoes and biting flies as both larvae and adults.
How long does a dragonfly live?
The flying adult usually lives only a few weeks to a couple of months. But most of a dragonfly's life is spent underwater as a nymph — for the green darner, typically several months to about a year, and in some dragonfly species several years. The nymph is a formidable aquatic predator in its own right, and the whole aerial adult stage is essentially a brief, intense phase for dispersal and reproduction.