How deadhead hawkmoths manage to fly straight in the dark

Sitting alone in the cockpit of a small biplane, Martin Wikelski listens to the signals of the car next to him. Sound beacons help ecologists track down beardies (Acherontius atrapas), hovering in the dark skies above Konstanz, Germany – about 80 kilometers north of the Swiss Alps.

The moths, named for the skull and crossbones pattern on their backs, migrate thousands of kilometers between northern Africa and the Alps in spring and fall. Many migrating insects go where the wind takes them, says Ring Karde, an entomologist at the University of California, Riverside, who is not a member of Wikelski’s team. Death’s head moths do not look typical.

“When I follow them on a plane, I use very little gas,” says Wikelski of the Max Planck Institute for Animal Behavior in Munich. “This indicates to me that they are supposedly picking directions or areas that are likely to be supported by a small amount of updrafts.”

The purple line marks the path taken by ecologist Martin Wikelski in his biplane as he tracked a peregrine falcon migrating south from Konstanz, Germany, to the Alps.Max Planck Institute of Animal Behavior

A new analysis of data collected from 14 insects shows that these insects do indeed steer themselves, perhaps relying in part on an internal compass tuned to the Earth’s magnetic field. Pray not only fly in a straight linethey also stay on course even when the wind changes, Wikelski and his colleagues reported on Aug. 11 Science.

The findings could help predict how butterfly flight paths might change as the globe warms, Wikelski says. He suspects that, like many other animals, the deadly moths are likely to move north in search of cooler temperatures.

To track the butterflies, Wikelski’s team taped radio transmitters to their backs, which is easier than you might expect. “Death’s head hawkmoths are totally cool,” Wikelski says. They are also huge. Weighing as much as three bobbins, the butterfly is the largest in Europe. This makes attaching the tiny tags easy, although moths don’t like it very much. “They talk to you, they yell at you a little bit,” he says.

close-up of a dead-headed hawk as the researcher places the tracker on its back
Researchers tracked deathhead moths similar to this insect by taping radio transmitters to the insects’ backs. Transmitters weighing less than 0.2 grams are a light lift for giant butterflies that can weigh up to 3.5 grams.Christian Ziegler/Max Planck Institute for Animal Behavior

After the researchers released the newly tagged and slightly irritated moths, Wikelski flew after them in a plane. As the insects flew south toward the Alps, an onboard device would beep the transmitters at a frequency related to the moth’s distance from the plane.

While detailed tracking of eight butterflies allowed him to track insects an average of about 63 kilometers, he pursued one insect just under 90 kilometers. This is the longest distance an insect has been continuously tracked, he says. “It’s an outrageously crazy job,” he says of the low-altitude night flights. “It’s also a little bit dangerous, and it just goes to show that it’s possible.”

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