By attaching tiny radio transmitters to dragonflies, scientists have learned that the insects migrate a lot like birds.
“They follow really simple rules,” said Martin Wikelski, an ecologist at Princeton and the lead author of the research in Biology Letters. “They just use temperature and wind.”
Wikelski used a transmitter-battery package weighing about one-hundredth of an ounce – about one-quarter of a dragonfly's weight. They were attached to the thorax with false-eyelash adhesive and Super Glue.
“Everybody thought this was totally crazy,” Wikelski said. “We didn't really expect it to work well.”
But of 14 green darners that were tagged in central New Jersey last fall, the scientists were able to track 13, following them by car or small plane and using signal strength to chart location.
The dragonflies headed south, generally, and were followed for about 35 miles, on average, over six days. (The tiny batteries die after about 10 days.) Like birds, they had days when they traveled (about every third day) and others when they rested. And like birds, they flew only when the winds were relatively weak (less than about 15 miles an hour) and when temperatures fell over successive nights (a sign of a cold front with prevailing southerly winds).
What is still a mystery, Wikelski said, is why these insects migrate. Presumably it's to find better breeding grounds, but only more and longer tracking will determine that.
“It's a question we can only really answer if we can follow individuals,” he said.
