Common Green Darner (Anax junius): Dragonfly Facts and Migration

What does a common green darner look like?

The common green darner is a big, strong-flying dragonfly. Both sexes have a plain, bright green thorax, the middle section of the body that carries the wings and legs. The large compound eyes meet on top of the head and are usually brownish or greenish.

Mature males have a bright blue to bluish-purple abdomen with a dark line along the top. Females and young males usually have a reddish-brown or purplish-brown abdomen, though some females are blue like the males. The wings are clear at first and often turn amber-tinted with age, especially in females.

A good field mark is a small black “bull’s-eye” spot on the top of the face, in front of the eyes, ringed with yellow or tan. It separates the green darner from the similar comet darner (Anax longipes), which has a bright red abdomen in males.

How big is a green darner?

Green darners are 6.8–8 cm (2.7–3.1 in) long with a wingspan of up to about 10–11 cm (4–4.3 in). Like most insects, they are very light, weighing roughly a gram.

Large darners are among the fastest insects in level flight; measured top speeds for large hawker-type dragonflies are usually given as roughly 36–54 km/h (22–34 mph). Speed claims well above that are not well documented.

Habitat and range

The common green darner lives across most of North America, from southern Canada through the United States and Mexico to Central America, and on islands in the Caribbean. It is native to Hawaii, where it is called pinao. Wind-blown vagrants have turned up as far away as Britain, France, Alaska and eastern Asia.

Green darners breed in ponds, lakes, marshes, ditches and slow-moving streams and rivers with plenty of water plants. They tolerate many kinds of standing water, including garden ponds and stormwater basins. Adults are strong fliers and are often seen far from water, hunting over meadows, farmland, parks and city streets.

The common green darner is the official state insect of Washington, adopted in 1997.

Diet and hunting

Common green darners are predators at every stage of life. Adults hunt in flight, catching flying insects such as flies, midges, mosquitoes, moths, flying ants, butterflies, wasps and even other dragonflies and damselflies. A darner typically grabs its prey with its spiny legs, which form a basket in front of the head, then bites it with powerful jaws and often eats it while still flying.

Darners are “fliers” rather than “perchers”. Instead of waiting on a twig and darting out, they patrol back and forth over water or open ground for long periods, scanning for prey. Their huge compound eyes, each made of more than 20,000 tiny facets in large dragonflies, give them nearly all-round vision and excellent motion detection.

The nymphs hunt underwater, ambushing aquatic insects, small crustaceans, tadpoles and small fish with a hinged, extendable lower lip. The details are in what do dragonflies eat?

Life cycle: eggs, nymphs and adults

Green darners mate in the typical dragonfly “wheel” position. Unusually for a North American darner, the pair often stays joined in tandem while the female lays her eggs, with the male holding her behind the head. She uses a blade-like ovipositor to insert the eggs one by one into the stems and leaves of water plants just below the surface.

The eggs hatch into aquatic nymphs, also called naiads or larvae. A nymph breathes through gills inside its rectum and can shoot water out of its rear end to jet away from danger. It grows by molting its skin many times.

Depending on temperature and generation, the nymph stage lasts from a few months in warm southern waters to about a year in the north. When it is fully grown, the nymph climbs out of the water onto a plant stem, usually at night, splits its skin and emerges as a soft, pale adult. The empty skin, called an exuvia, is often left clinging to the plant.

Adults live for a few weeks on average. Read more in how long do dragonflies live?

Behavior: patrols, territories and warming up

Mature male green darners spend much of the day patrolling over ponds and marshes, flying steady beats a meter or so above the water along the shoreline and over open water. A male defends a stretch of shore against other males, chasing rivals in fast, twisting pursuits, and tries to grab any female of his species that arrives to lay eggs.

Females and young adults spend more time away from water. After emerging, a new adult goes through a maturing period of days to a couple of weeks, during which its colors develop and its flight muscles harden. It feeds over fields, woodland edges and gardens before returning to the water to breed.

Like other large dragonflies, green darners need warm flight muscles to fly well. On cool mornings they can raise their body temperature by “wing-whirring”, a rapid shivering of the wings while perched, much as a bumblebee shivers before take-off. In hot weather, a flying darner can shed heat by circulating warm blood from the thorax into the long abdomen.

How to tell a green darner from look-alikes

Several large dragonflies share the green darner’s green thorax and long abdomen. These features help to tell them apart:

Mosaic darners of the genus Aeshna, common in both North America and Europe, look different on closer view: their thorax is brown or dark with bright stripes or spots rather than plain green.

Migration: a journey of several generations

The common green darner is the best-studied migratory dragonfly in North America. Each year, large numbers fly south in late summer and fall, sometimes in loose swarms along coastlines and ridges, and others move north in spring.

A study using stable isotopes, published in 2018, analyzed the hydrogen isotopes locked into the dragonflies’ wings, a chemical signature of the water in which each insect grew up as a nymph, which reveals roughly where it came from. It showed that the annual cycle involves at least three generations. The first emerges in the south in early spring and flies north. Its offspring emerge in the north in summer and migrate south in fall. A third generation develops in the south over the winter and does not migrate.

Earlier work fitted green darners with tiny radio transmitters. Tracked dragonflies migrated on some days and rested on others, covering up to about 140 km (87 mi) in a day, and they tended to set off after nights with falling temperatures, similar to migrating songbirds. A 2019 study using a radio-tracking network found an average ground speed of about 16 km/h (10 mph). The pattern is comparable to that of the monarch butterfly.

Not every green darner migrates. Some populations, especially in the south, are resident and breed in the same area all year.

Predators and threats

Fish are the main predators of green darner nymphs, along with diving beetles, other dragonfly nymphs, frogs and wading birds. Adults are caught by birds such as kestrels, swallows, purple martins and flycatchers, and occasionally by robber flies, spiders and larger dragonflies.

The species is widespread and abundant, and the IUCN lists it as Least Concern. Like all dragonflies, it depends on clean, plant-rich fresh water for breeding, so draining and polluting wetlands harm local populations.

Myths and facts

“Dragonflies sting.” Green darners have no stinger. The long abdomen ends in harmless appendages, and the female’s ovipositor is used only to place eggs in plants. The real story is in do dragonflies bite or sting?

“Darners sew up people’s lips.” The old names devil’s darning needle and darning needle come from folklore that warned children about dragonflies sewing up their mouths or ears. It has no basis in fact.

“A green darner is the same as a damselfly.” Damselflies are close relatives in the same order, Odonata, but they are smaller and more slender, with widely separated eyes and wings that usually fold together at rest. See dragonfly vs damselfly.

Green darners and people

For many people in North America, the green darner is the first dragonfly they learn to recognize. It is common around park ponds, golf courses and gardens with water, and its migration attracts birdwatchers and naturalists who count passing darners in fall.

Dragonflies also help scientists judge the health of wetlands. Because the nymphs need clean, oxygen-rich water with plenty of plants, a pond full of breeding dragonflies is usually in good condition. Europeans who want to see a similar insect can look for the emperor dragonfly, Anax imperator, a close relative with a blue abdomen and green thorax.