(All pictures from www.princeton.edu)
Blue Ridge Blue Collar Man and I were talking at supper last night when he mentioned something he’d heard on NPR, on Fresh Air (with Terry Gross). “Did you know that dragonflies migrate like birds?” he said. “And that they fatten up before migrating, just like birds?”
I stopped in mid-chew. “No…that’s amazing!” And just like that, as we ate our flounder, my Friday Fact was born. When Tom mentioned this, I remembered a conversation we’d had at supper about two months earlier. Then, Tom had told me about a friend of his at work, a very masculine tough guy, who had related his experience to Tom with the awe and wonder of a child . He told Tom that he was driving down his driveway in Linville Falls when, suddenly, he encountered thousands of dragonflies flying in front of his truck in a cloud so thick he had to stop.
Scientists have only recently developed the technology to study the migration patterns of dragonflies. (The problem was making a transmitter tiny enough not to weigh down the flying insect). Only about a dozen of the approximately 400 known dragonfly species in the United States and Canada are known to migrate. The most prevalent of these is the Green Darner dragonfly (Anax junius), which is the one they have primarily been studying.
Martin Wikelski, a professor of ecology and evolutionary biology at Princeton University is leading the study. He follows the dragonfly migration with the help of tiny transmitters, weighing .01 ounces, glued (with eyelash adhesive!) to the dragonfly’s underside. He carries a receiver that picks up the transmissions, but because they move around so much, he has to follow and track the dragonflies in his airplane.
What they have found so far is that the migration of dragonflies is very similar to that of birds. Like birds, they migrate in the fall. “The dragonflies’ routes have showed distinct stopover and migration days, just as the birds’ did,” said Professor Wikelski. “Additionally, groups of both birds and butterflies did not migrate on very windy days and only moved after two successive nights of falling temperatures.” [This means a cold front is moving in with a tailwind that will aid their flying] “We saw other similarities as well, which makes us think that dragonflies find their way south using natural landscape features, such as seacoasts and large rivers.”
And, like migrating monarch butterflies, the dragonflies migrating south will not be the ones making the return trip. It will be their offspring flying back north in the spring.
Another interesting pattern was discovered by a birdwatcher named Frank Nicoletti who was studying hawk migration when he noticed that the migration of the dragonflies coincided with the migration of juvenile American kestrels. The thick clouds of migrating dragonflies made it easier for the inexperienced young falcons to catch their dragonfly meals, so the insects are an important food source for the migrating kestrels.
And, of course, I just had to know where the Green Darner dragonfly got its name. Just as I suspected, the name came from its resemblance to a darning needle (the big one used to mend holes in sweaters and socks). In fact, one of its nicknames is “darning needle.” Apparently, some parents used to tell their children to be careful not to let the dragonfly get near their mouth because it might stitch it closed with its darning needle!
Hmmm. So that’s what parents mean when they say, “Darn that kid!” :-)