DRAGONFLIES

The annual flight of the dragonflies goes mostly unnoticed, though it is one of the great migrations of flying creatures that occur across North America . The dragonfly is an exceptionally beautiful insect and a fierce carnivore. It has four wings that beat independently. This gives it an ability to maneuver in the air with superb dexterity. A dragonfly can put on a burst of speed, stop on a dime, hover, fly backward, and switch direction in a flash. This is a hunting behavior known as hawking. Dragonflies kill their pretty in the air and eat it on the wing. They feed on aerial plankton, which consists of any sort of small living thing that happens to be aloft – mosquitoes, midges, moths, flies, ballooning spiders.

            Several species of dragonflies migrate in North America ; one is the common green darner, which is about three inches long and has a wingspan of around four inches. It has a green thorax, a long abdomen of cerulean blue with a black stripe, clear wings, and bulging eyes the color of a Spanish olive. Green darners never attack people, but they have been seen bringing down hummingbirds. They are the Bengal tigers of the microworld.

            A dragonfly spends a large portion of its life underwater as a nymph, eating tiny aquatic animals. One day, the nymph climbs up on a twig and splits open, and an adult dragonfly called a teneral emerges. At the end of summer, tenerals fly south. They travel on sunny days just after a cold front has come through, riding on north winds. They go from Canada as far south as Veracruz , Mexico , covering as much as fifty miles a day. They have keen eyesight, and they follow topographical lines on the land – ridges, valleys, and especially shorelines.

            In North America , the main migration path of the green darners follows the Atlantic shoreline past New York City, but swarms of them are rarely spotted. In 1916, R. C. Osborn reported a swarm above Long Beach , on Long Island . In 1992, another darner swarm was spotted over Fire Island . That was it.

            “We don’t know anything about what the dragonflies do when they get in the vicinity of the city,” Michael L. May, a professor of entomology at Rutgers University , said. One day a few weeks ago, just after a cold front, he stood on a spit of land at the southern tip of the Verrazano Narrows , looking through binoculars. “You’d see them passing by one at a time, every minute or so,” he said. He swilled the binoculars toward Coney Island . “In all the years I’ve looked, I’ve only seen one mass dragonfly migration, in northern Florida .”

-- Richard Preston in The New Yorker