Anax junius

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Green Darner Migration

Common green darner female (Anax junius)

On a windy, warm September evening, the sun has set; the air is soft and dusky. Migration is underway, but not the avian sort. A few large common green darner dragonflies zigzag beneath the trees hawking insects. I look skyward and far above me, a river of swarming green darners surges — hundreds of them — straight south ahead of a cold front.

Born in Minnesota, these green darners migrate to the Gulf Coast of the southern United States and Mexico. When they arrive, they’ll mate and lay eggs to produce the next generation, which will migrate north in April or May. When they arrive here, they will mate and give rise to a new generation before dying. These progeny will hatch by late August and continue the cycle of migration and reproduction. 

But that’s not the entire story! Common green darners are present in the north all summer — so where did they come from? There’s a resident population that doesn’t migrate. They’re active and deposit eggs throughout the summer and autumn. However, their young, called naiads, won’t mature until the following spring. They will wait out the winter on the bottom of a pond, marsh or slow-moving river or stream.

Averaging 3 inches in length, and with a wingspan of 3.5 inches, green darners are among our largest dragonflies. This one also is a female. Males’ abdomens are bright blue.

Green darner adults eat mosquitoes, midges and other flying insects. The aquatic naiads feast on mosquito larvae and other aquatic insects, tadpoles and tiny fish. Green darners are eaten by spiders, large robber flies and birds such as kestrels.

Further Reading

Mead, Kurt. (2009). Dragonflies of the North Woods. Duluth, Minnesota: Kollath & Stensaas Publishing.

Smithsonian Magazine

UW-Milwaukee Field Station

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Garden Damsels and Dragons

A thread-slender eastern forktail (Ishnura verticalis) damsel fly.

A thread-slender eastern forktail (Ischnura verticalis) damsel fly.

The early morning garden is a place of shadows and peace. Cardinals, goldfinches, mourning doves and house wrens ring out their song in neighborhood trees. Already, bumblebees work the flowers — bluebells, bee balm, hyssop and milkweed — buzzing softly.  Almost camouflaged in the deep green shadows, a tiny damselfly perches atop a milkweed leaf. An eastern forktail (Ischnura verticalis), its slender body, less than an inch long, is mint green, blue and black. The wings are folded over its back in damselfly style.

Across the backyard, a much larger dragonfly relative hangs from the edge of a hosta leaf, wings held away from its body horizontally. It is a green darner (Anax junius), one of the largest dragonflies in the world at three inches in length and with a wingspan of more than four inches. Its spring-green head and thorax hide it among the hosta. It “wing-whirs”, or rapidly vibrates its wings to warm up its flight muscles — and that movement catches my eye and reveals its presence.

A common green darner (Anax junius) is one of the largest dragonflies.

A common green darner (Anax junius) is one of the largest surviving dragonflies.

Damselflies and dragonflies are members of the order Odonata, which means “toothed ones”. Unlike the peaceable bumblebees, they are fierce predators, hunting for small insects in the garden and eating many pests. Odonata are descended from some of Earth’s most ancient creatures. Fossils of ancient dragonfly ancestors (Protodonata) date back 325 million years. Scientists believe that bees evolved more recently — about 120 million years ago; the oldest bee fossil discovered so far is about 100 million years old. Both insect families contribute to a healthy garden.