Moth mystery solved
Trillions of insects migrate across the globe each year, yet little is known about their journeys.
So to look for clues, scientists in Germany took to the skies, placing tiny trackers on the backs of giant moths and following them by plane.
To the researchers’ surprise, the moths seemed to have a strong sense of where they were going.
Even when the winds changed, the insects stayed on a straight course, the scientists reported in a study published yesterday in the journal Science.
Their flight paths suggested these death’s-head hawk moths had some sort of complex navigation skills, the authors said, challenging earlier ideas that insects were nothing more than wanderers.
“For many, many years, it was thought that insect migration was mostly just dictated by winds, and they were blowing around,” said lead author Myles Menz, now a zoologist at James Cook University in Australia.
It had been tough for scientists to get a close look at how insects travelled, in part because of their small size, Menz said. The kinds of radio tags used to follow birds can be too heavy for smaller fliers.
But transmitters have become tinier. And it helps that the death’shead hawk moth is huge compared to other insects, with a wingspan up to 127mm.
The iconic species — dark coloured with yellow underwings and skull-like markings — was able to fly well with the tiny tracker glued to its back, said Martin Wikelski, a study co-author and migration researcher at Germany’s Max Planck Institute for Animal Behaviour.
The moths are thought to migrate thousands of kilometres between Europe and Africa in the autumn, flying by night.
For the study, researchers released tagged moths in Germany in the hopes they’d start flying on their migration path toward the Alps.
Wikelski, the study’s pilot, took off in his plane, circling the area and waiting for any moths on the move. If he did pick up a signal from a tiny traveller, he would follow its radio blips for hours at a time.
“The little moth is guiding you,” he said.
The researchers followed the flight paths of 14 moths, with their longest track about 90km.
Not only did the moths fly in straight lines, but they also seemed to work around wind conditions, Menz said, flying low to the ground when the winds were against them, or rising up to catch a helpful tail wind.