These butterflies flew across the Atlantic Ocean, winging their way from Africa to South America!

The concept of the butterfly effect suggests that a butterfly flapping its wings in one part of the world could lead to a storm on the other side of the globe. But what if the butterfly flaps its wings all the way from one part of the world to the other?

In a remarkable real-world twist, researchers have documented painted lady butterflies making an astonishing 4,200-kilometre journey across the Atlantic Ocean—from Western Africa to the shores of French Guiana in South America!

From flap to finish: Decoding the butterflies’ origins

Back in October 2013, Gerard Talavera from the Botanical Institute of Barcelona at CSIC stumbled upon painted lady butterflies on the Atlantic beaches of French Guiana. This peculiar sighting, considering these butterflies aren’t usually found in South America, sparked an international research effort to trace their origins.

The research team employed advanced tools to trace the butterflies’ journey. They started by analysing wind trajectories from the time leading up to the butterflies’ arrival in October 2013. The data revealed unusually favourable wind conditions that could support a transatlantic flight from West Africa, suggesting these butterflies might have flown across the ocean.

By sequencing the genomes of the butterflies and comparing them with global populations, the researchers found a genetic closeness to African and European butterflies, ruling out North American origins and reinforcing the theory of an oceanic flight.

The team then used cutting-edge molecular techniques to sequence the DNA of pollen grains carried by the butterflies. They identified plant species that only grow in tropical Africa, indicating that the butterflies had nectared on African flowers before their oceanic voyage.

Finally, they analysed hydrogen and strontium isotopes in the butterflies' wings, which serve as a chemical fingerprint of their place of origin. The isotope analysis, combined with habitat models for larval growth, pointed to a possible natal origin in Western Europe, possibly France, Ireland, the United Kingdom or Portugal.

Combined, these findings suggest that the painted lady butterflies took birth in Europe, migrated to West Africa, and then made an epic flight across the Atlantic to reach the eastern coast of South America!

“We usually see butterflies as symbols of the fragility of beauty, but science shows us that they can perform incredible feats. There is still much to discover about their capabilities,” said Roger Vila, a researcher at the Institute of Evolutionary Biology (CSIC-Pompeu Fabra University) and co-author of the study.

Harnessing the Saharan winds

Elaborating on how they managed this feat, Eric Toro-Delgado, one of the article's co-authors, explained: “The butterflies could only have completed this flight using a strategy alternating between active flight, which is costly energetically, and gliding the wind. We estimate that without wind, the butterflies could have flown a maximum of 780 km before consuming all their fat and, therefore, their energy.”

The butterflies likely made use of the Saharan air layer, a conveyor of dust from Africa to the Americas. These wind currents, known to fertilise the Amazon with Saharan dust, also appear to be a highway for living organisms.

In fact, this transatlantic flight points towards the existence of natural aerial highways linking continents, which could enable species dispersal on a far greater scale than we ever thought possible.

With global warming and evolving climate patterns, scientists warn that we might see more pronounced shifts and a surge in such long-distance dispersal events. These changes could profoundly influence biodiversity and ecosystems across the globe.

These findings were recently published in Nature Communications and can be accessed here.