Scientists have found the first evidence of insects crossing an entire ocean – after finding butterflies making a 2,600-mile journey across the Atlantic Ocean.
Gerard Talaveraan evolutionary biologist at the Botanical Institute of Barcelona, made the discovery in 2013 in French Guiana, when he saw a flock of painted lady butterflies (Vanessa cardui) sitting on the sand, their wings torn and pierced with holes.
This discovery puzzled scientists because the tiny species is found all over the world, but not in South America. Now, after ten years of research, the researchers have found an answer to the question of how the butterflies got there: they embarked on the first transoceanic flight recorded in an insect.
The researchers published their findings Tuesday (June 25) in the journal Nature communication.
“We tend to see butterflies as a symbol of the fragility of beauty, but science shows us that they can perform incredible feats,” study co-author Roger Villaa researcher at the Institute of Evolutionary Biology in Barcelona, said in a statement. “There is still a lot to discover about their capabilities.”
Insect migrations are not uncommonbut they are difficult to track. Scientists usually rely on data from amateur insect observers and radar coverage to study insect movements, but these are limited and not always reliable.
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To find out how the painted lady butterflies ended up in French Guiana, the researchers collected several pieces of evidence. They mapped the butterflies’ genomes, which showed they were closely related to populations in Europe and Africa. The team also analyzed pollen DNA on the 2-inch-long (5 centimeters) bodies of the insects and identified two plant species found only in tropical Africa. They also studied isotopes of hydrogen and strontium on the wings of the butterflies, finding that these were unique to Western Europe.
Taken together, this evidence ruled out a North American origin for the insects and suggested that their lives began in Africa or Europe.
“The painted lady butterflies reached South America from West Africa, flying at least 4,200 km across the Atlantic Ocean. But their journey could have taken even longer, starting in Europe and passing through three continents, implying a migration of 7,000 km. [4,350 miles] or more,” co-author studied Clement Bataille, a professor of earth and environmental sciences at the University of Ottawa in Canada said in the statement. “This is an extraordinary achievement for such a small insect.”
Painted lady butterflies are already known to migrate up to 14,500 km between Europe and Africa, including crossing the unforgiving expanse of the Sahara.
But this journey is made with overnight stops to rest and refuel. To reach French Guiana from West Africa, the butterflies would have to fly for up to eight days without rest.
To solve this part of the mystery, the scientists analyzed wind currents rising from the Sahara and blowing dust from Africa to the Americas. They discovered that the butterflies could complete their remarkable journey by gliding over these airways.
“The butterflies could only have completed this flight using a strategy that alternated between minimal effort to avoid falling into the sea, facilitated by rising winds, and active flight, which requires more energy expenditure,” study co-author Eric Toro Delgado, a PhD student at the Institute of Evolutionary Biology said in the statement. “We estimate that the butterflies could have flown a maximum of 780 km without wind [485 miles] before they have exhausted all their fat and therefore their energy.”
The finding highlights the ability of insects to travel enormous distances in ways scientists had not previously considered.
“This discovery opens new perspectives on the ability of insects to disperse over long distances, even across seas and oceans. It is possible that we underestimate the frequency and impact of these movements on our ecosystems,” lead author Talavera said in the study statement. “Throughout history, migration phenomena have been important in defining the distribution of species that we observe today.”