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News picture Common green darner

 

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Bug of the Month: Common green darner

Overhead view of common green darnerCommon name: Common green darner

Latin name: Anax junius

Taxonomy:
Kingdom Animalia
   Phylum Arthropoda
      Class Insecta
         Order Odonata
            Family Aeshnidae

 

Dragonflies in general

Dragonflies are the “charismatic megafauna” of the insect world.  They are large, often brilliantly colored, fast-flying, and fierce predators. Many can be identified on the wing, or in the net, without further magnification. Although people often refer to all of the Odonata as “dragonflies,” the order includes both dragonflies and their close relatives, the damselflies. Damselflies are generally distinguished by smaller and slenderer bodies, eyes set far apart, and most hold their narrow wings above them when at rest. The eyes of dragonflies touch each other, and they hold their broader wings out to the sides at rest. The large eyes and tiny antennae of dragonflies tell you that these predators rely primarily on sight to hunt their prey (including mosquitoes!), which they usually catch while in flight. 

Dragonflies are a primitive group of insects. They have been around for over 300 million years, and fossils indicate that giant ancestors with wingspans of over two feet used to fly over ancient swamps.  There are about 6,500 odonate species (including damselflies) worldwide, 450 in North America, and about 170 in MA.

How to identify common green darners

WIng of common green darnerThis is a large dragonfly (almost 3 inches long) with a bright green thorax. The long abdomen is blue for males, with a dark stripe on top, and females have a brown or purple abdomen, also with a dark dorsal stripe. The wings in both sexes have yellow edges in the front and are often faintly amber-colored.  In life, the large eyes are brown for females, and more greenish-yellow for males. Both sexes also have a “bull’s eye” pattern on the forehead.

Where to find common green darners on the Boston Harbor Islands

Common green darners breed in weedy freshwater wetlands, ponds, and slow rivers. These habitats are rare to non-existent on the islands, so the common green darners we see are usually feeding (sometimes in swarms) or they may be migrants (see below). This species is active for a longer time during the year than any other dragonfly—you might see these darners as early as April, and as late as November.

Front of common green darner headClose-up of head of common green darner

 

How common green darners make a living

Like all odonates, common green darners spend their immature life stages as nymphs in still bodies of water. The nymphs are fierce predators also, and hide out in dense, weedy places, surprising their prey which can include tadpoles and small fish. Development from nymph to adult may take anywhere between one summer and several years, depending on the water temperature. After metamorphosis, adults emerge from the water and will live only a few weeks to two months, during which time they need to mate, and the female lays eggs. To mate, the male and female form a “mating wheel” where the male grasps the female behind the head with the end of his abdomen, and the female touches the end of her abdomen up under the male to where sperm are stored. The male holds onto the female while she lays eggs in plant stems or rotting wood at the edge of the water. Some, but not all, populations of common green darners are migratory, moving north in the spring and south in the fall. Each individual migrates only one direction, its offspring will make the return trip.  Migration routes are often along the coast (see website below).

Side of common green darner

Where in the world common green darners occur

This species is found across southern Canada, in all 50 states of the U.S., south to Mexico, Honduras, and most of the Caribbean island groups. Strays have been seen in Asia and Great Britain.

To learn more about common green darners (and dragonflies in general)

On the web:

In print:

    Carpenter, V. 1991. Dragonflies and damselflies of Cape Cod. The Cape Cod Museum of Natural History, Natural History Series No. 4.

    Dunkle, S.W.  2000. Dragonflies through binoculars: a field guide to the dragonflies of North America.  Oxford University Press, New York, NY.

    Lam, E. 2004. Damselflies of the Northeast. Biodiversity Books, Forest Hills, NY.

    Needham, J.G., M.J. Westfall, Jr., and M.L. May.  2000. Dragonflies of North America.  Scientific Publishers, Gainesville, FL.

    Nikula, B., J.L. Loose, and M.R. Burne. 2003. A field guide to the dragonflies and damselflies of Massachusetts.  Mass. Div. of Fish and Wildlife, Natural Heritage and Endangered Species Program.