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ScienceShot: Butterfly Migration Mystery Solved

Liz is a staff writer for Science.

Monarchs aren't the only continent-hopping butterflies. Painted ladies, common on the European continent and in the United Kingdom, are also long-distance commuters, traveling back and forth to North Africa, a new study shows. Although the insect's northward trip was well-documented by citizen scientists, few saw it heading south again—suggesting the commute might be just one-way. But in the spring of 2009, millions of painted ladies hit the shores of the United Kingdom, offering up an abundance of new data. With many observations to work with, researchers correlated some of the 60,000 sightings with data from radars that monitor insect movements above 150 meters. The radar revealed a high-altitude southward migration route: Most painted ladies ascend to 500 meters or so to hitchhike rides on the upper air's fast moving winds, ecologists reported this week in Ecography. The insects—the offspring of the northward-traveling migrants—tended to leave for North Africa in two waves, one in August and one in October, sometimes traveling more than 50 kilometers an hour—twice as fast as they can fly on their own, say the researchers. Based on radar sightings, in 2009 11 million painted ladies landed in the United Kingdom and 26 million left—indicating that, far from being a dead end, the British Isles gave the species a boost.

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Posted in Plants & Animals