Utilizing the winds blowing from the Sahara Desert in Africa to South America, the tiny Vanessa cardui butterfly can fly continuously for 5 to 8 days across the ocean.
In 2013, entomologist Gerard Talavera from the Barcelona Institute of Botany was astonished when he spotted several Vanessa cardui butterflies on a beach in French Guiana, South America. This species regularly migrates 14,500 kilometers from Europe to the Sahel region of Africa, but they stop along the way to rest and replenish energy. To reach South America, they must fly non-stop across the Atlantic Ocean.
Vanessa cardui butterflies can fly across the Atlantic without resting. (Photo: Roger Vila).
For the past 10 years, Talavera and his colleagues have been investigating why Vanessa cardui butterflies can fly such long distances. A study published in the journal Nature Communications on June 25 revealed that they may have completed a 4,200-kilometer journey across the Atlantic from West Africa with the help of favorable wind conditions.
In this new study, the research team examined weather data from several weeks before the butterfly swarm arrived in South America. They also sequenced the genes of Vanessa cardui and discovered that they are relatives of insects found in Africa and Europe, ruling out the possibility that they originated from North America. Additionally, analyses of isotopes in the butterfly wings indicated that they originated from Western Europe and West Africa.
Next, the research team sequenced the DNA of pollen grains found on the butterflies’ bodies to identify the plant species they had recently encountered. The results indicated that the butterflies had interacted with Guiera senegalensis and Ziziphus spina-christi, two shrub species that flower at the end of the rainy season in West Africa. Overall, the research team concluded that the Vanessa cardui butterflies indeed flew from West Africa to South America, crossing the Atlantic Ocean—an unprecedented feat.
Wind is a particularly crucial factor in this journey, which scientists estimate lasts 5 to 8 days. The air currents known as the Sahara Air Layer carry dust from the Sahara Desert in Africa to South America, helping to fertilize the Amazon River Basin. Sometimes, dust travels as far as Florida, temporarily preventing storms. Now, scientists understand that the Sahara Air Layer is also important for insects.
“Butterflies can only complete this flight by alternating between active flying—an energy-intensive activity—and gliding on the wind. We estimate that without the wind, they could only fly a maximum of 780 kilometers before exhausting their fat and energy,” concluded Eric Toro-Delgado, a biologist at the Institute of Evolutionary Biology in Spain and a co-author of the study.
