Migrating Moths Are Good Navigators

The silver Y moth has pale brown wings with a distinctive silvery white Y-shaped marking on each forewing. Credit: Ian Woiwod / Rothamsted Research.

To most of us, moths are nothing more than strange homebodies that can't leave a light bulb alone. But every year, millions of moths hop aboard wind currents and flutter hundreds of miles southward to suitable mating lands. The migrating moths are not totally at the mercy of the wind — they are equipped with compasses, a new study suggests.

"There has been speculation for many years about whether insects that rely on the wind for their migrations can have any control over the direction in which they migrate," said lead researcher Jason Chapman of Rothamsted Research in England.

Without flight control, the furry insects could land in unsuitable spots and die.

Using a radar-beam technique, Chapman and his colleagues monitored about 200 million silver Y moths (Autographa gamma), a plant-feeder that migrates at night, flying southward over the U.K.

Results, detailed online today in the journal Current Biology, show most of the moths took wing only on nights with south winds. Once airborne, the moths expedited their commute by flying in a roughly downwind direction while concentrating at altitudes with the fastest winds.

The moths also compensated when the wind direction was way off target.

"When the wind is not exactly aligned with their preferred direction, they take this into account and head off in a direction that will partially compensate for this wind drift," Chapman told LiveScience. "However, how they do this remains a mystery, as they somehow have to detect the wind direction while flying hundreds of meters above the ground and in very low light levels."

Chapman suspects the moths use a geomagnetic compass to stay on track, similar to the type found in migratory birds.

Study funding came from the Biotechnology and Biological Sciences Research Council and the Volkswagen Foundation.

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