THIS STORY ORIGINALLY appeared on WIRED Italia and has been translated from Italian. The dozen butterflies were flying gracefully over a beach in French Guiana when Gerard Talavera spotted them. It only took a moment to see they were extraordinary.
These were not just any butterflies, he saw, but painted ladies ( Vanessa cardui )—beautiful orange, white, and black insects that do not live in South America. They migrate regularly from Europe to sub-Saharan Africa, but stop several times during their travels to rest. To reach this beach, Talavera realized, they would have to have traveled more than 4,200 kilometers, crossing the Atlantic Ocean without a break.
That was back in 2013. Now, after 10 years of research, Talavera—an entomologist at the Barcelona Botanical Institute—working with an international research team has proven that the insects did in fact cross the Atlantic, and they think they know how, too. The details of this long migration have been published in Nature Communications .
To trace the butterflies’ mysterious journey and prove their origin, the team carried out a number of analyses. Although migratory insects like butterflies are numerous, it’s very difficult for scientists to track them: Researchers cannot, for example, attach tracking devices as they would with other animals, because these are often too large and heavy to be carried by the insects. Clues as to the butterflies origins had to be gleaned from other datasets.
First, the team examined.