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Sunday, October 31, 2010

The last dragonflies of the year -- or are they?

Green darner dragonly, Anax junius. 
I watched this green darner dragonfly couple laying eggs in the new pond at Brooklyn Bridge Park. The male is in front, clasping the female by the head. They mated just a few minutes before.

They worked like a couple on a bicycle-built-for-two, taking a few synchronized steps forward or back as she found spots she liked. Her abdomen has a sharp tip to make little slits in aquatic vegetation. She makes a slit, places an egg, and then they move on. The couple flew from branch to branch, scattering their eggs.

This is the beginning of a dynasty for that pond. The eggs will soon hatch into larvae that will spend the winter (and several more years and developmental stages) actively hunting under water. Dragonfly larvae are voracious predators of other aquatic insects; in a pond too small for fish, the dragonflies will be top predators.

Green darners are the largest, most abundant, and most common dragonfly in North America. Adults are about three inches long with a four-inch wing-span. They have green bodies, yellow leading edges on their wings, and a blue-yellow-and-black bull's eye mark on the "forehead" between the eyes. The male has a handsome blue abdomen.

Green darner adults are so good at catching and eating mosquitoes that they are commonly called "mosquito hawks."

Some populations of green darners migrate south to warm areas at summer's end. Their descendants fly north in spring. Adult populations of northern residents and migrants spend the mosquito days of summer side by side. Larvae are at work below the water's surface year round.

And starting this year in the new pond at Brooklyn Bridge Park!


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