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What Time is it in Nature: Common Green Darner

August 30, 2014

It’s the time of year where many animal species start to move about the world. Some very long and impressive migrations are about to happen or are currently in progress, but most people tend to think about birds or mammals on the move if they consider migrations at all. There are some impressive insect migrations as well, and one species, the Common Green Darner (Anax junius) is currently making its way through North Carolina as it moves from its cooling summer habitats to more favorable climes further south.

Green darner dragonfly

Common Green Darners are dragonflies in the insect order Odonata (dragonflies and damselflies) and family Aeshnidae (darners). Within the US, they are one of the larger and more distinctive dragonflies. They have huge yellow-brown or greenish eyes that wrap around most of the top and sides of their heads with an eye or bullseye-shaped mark on the face just in front of the eyes. The thorax, the middle section, is vibrant green. Depending on whether you are looking at a male or a female, the abdomen can be a variety of colors. Males have a bright blue abdomen while the females have a green or purple-brown abdomen. The differences in colors make the Common Green Darner sexes easy to distinguish, even from afar.

Like other dragonflies, Common Green Darners have a complicated method of reproduction. Females choose their mates not by any merits of his own, but on the quality of the egg-laying habitat in which he resides. Males will fight with one another for the best locations and the strongest individuals with the best egg-laying habitats generally mate with more females than other males. When a female, who normally spends most of her time feeding away from the water, decides she wants to mate and approaches a pond to find a suitable place to lay her eggs, the male who protects that location will swoop in and grab her behind the head. The female will then have to curl her body up and under his to mate. After a brief mating session, they will together find a place where she will lay her eggs in the pond. In order to ensure that no other males have a chance to mate with the female before she lays her eggs, the male will continue to hold onto his mate’s head until she has laid her eggs and leaves the pond entirely.

Many dragonfly species spend the bulk of their lives in water as either eggs or immatures (called nymphs), and the Common Green Darner is no exception. After some time in the water, the nymphs will hatch from the eggs. The young dragonflies are tiny at first, but fierce! They are amazing predators that use a long, extendable mouthpart to reach out and grab prey (insects and small crustaceans, fish, or tadpoles) and pull it back to their face to eat. As they feed, they’ll grow, often going through over 20 molts over 1-3 years before they mature enough to leave the water. At that point, they’ll crawl out of the water, break open their final nymphal exoskeleton (they “shed their skin”), pull their bodies free, puff up their wings, and fly off in search of food. They’ll spend about a month on land as adults, hunting insects on the wing.

Only a handful of dragonfly species are known to migrate (though there may be others we’re not yet aware of), but Common Green Darners are one of the best known dragonfly migrants. In the fall, cues in the weather drive the dragonflies south. Scientists don’t really know where the Green Darners go once they leave the US, but they follow the east coast and the large midwestern rivers along the way, eventually striking out across the Gulf of Mexico and disappearing into Central or South America. They likely mate, lay eggs at their final destination, and die, with their children making the return trip in the spring.

We have Common Green Darners at Prairie Ridge throughout most of the late spring and into the early fall, but their numbers may increase dramatically as the migration begins. Next time you visit, take a trip down to the pond and look for the large brilliant green and blue dragonflies flying out over the open water. You’ll likely spot a mating or a duel between males, but if you’re lucky you just might get to see dozens of Darners, weary travelers taking advantage of the abundant prey in the prairie grasses as they rest on their long trip south.

What Time is it in Nature is a weekly feature highlighting the current plants, animals, and other wildlife at the Museum’s public outdoor facility, Prairie Ridge Ecostation. Find out more about the natural happenings at Prairie Ridge at our What Time is it in Nature Archive!

Photo by Chris Goforth

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