As a group of butterflies flew 2,600 miles across the Atlantic Ocean without stopping

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Painted lady butterflies go far with their impressive migratory patterns that stretch for thousands of miles – but they often travel across land, so they can stop to rest.

Scientists have now found evidence that a group of winged travelers flew more than 2,600 miles (about 4,200 kilometers) across the Atlantic Ocean without stopping, according to a new study published June 25 in the journal Nature Communications.

The discovery ends a decade-long mystery that began when entomologist and lead study author Dr. Gerard Talavera came across about 10 painted lady butterflies, known by the scientific name Vanessa cardui, on a beach in French Guiana in October 2013. The insects, which are not usually found in South America, were tired with holes and tears in their arms.

“They looked exhausted. They couldn’t even fly much – they hopped instead of flying,” said Talavera, a senior researcher at the Spanish National Research Council at the Botanical Institute of Barcelona. “The only explanation I could think of was that these were long-distance migrants.”

But crossing an entire ocean was unheard of for butterflies, even those of the world like painted ladies. Talavera, along with his colleagues, had to rule out several factors before concluding that these butterflies accomplished what was previously thought impossible.

An October 2016 study that Talavera co-authored found that painted ladies from Europe migrate long distances of about 2,500 miles (about 4,000 kilometers) to sub-Saharan Africa, crossing barriers such as the Mediterranean Sea and the Sahara desert. But even so, the butterflies mostly remain above ground where they can “stop and refuel, feed on flowers and then get energy to continue,” Talavera said.

According to the new study, crossing the Atlantic would take a painted lady butterfly five to eight days, depending on various variables.

Based on analyzes of energy constraints, the researchers concluded that the butterflies could fly a maximum of 485 miles (780 kilometers) without stopping, but favorable wind conditions are what allowed them to complete the long journey, Talavera said.

“This is actually kind of a record for an insect, especially a butterfly, to make such a long flight without an opportunity to stop,” said Talavera, who also directs the Painted Lady Migration Project in world, a global citizen science project that tracks insect migration routes.

There have been other cases in which experts suspect butterflies and other migratory insects travel longer distances than usual, returning to boats, remote islands or places where they are not normally found, Talavera said.

Researchers believe these butterflies took part in their annual migration south from Europe but were lost when the wind blew them into the ocean, he added. The butterflies then likely crossed the trade winds, which blow from east to west near the equator, until they reached land in South America.

“Hovering in the air column at the right height to take advantage of the trade winds is nothing short of extraordinary,” said Dr. Floyd Shockley, collections manager for the entomology department at the Smithsonian National Museum of Natural History in Washington. DC, which was not part of the new study. “It kind of begs the question, have they been doing this for a long time and we never documented it because we weren’t looking for it in South America?”

The discovery of about 10 butterflies abroad, versus the occasional singles that were likely caught in the storms, may be enough evidence that this was a coordinated migration event for the insect group, Shockley said.

The researchers took several important steps to confirm that these misplaced butterflies have indeed traveled across the ocean.

First, to rule out that the insects did not travel overland from North America, the researchers analyzed their DNA, finding that it matched that of European-African populations. Next, the team used a technique known as isotope tracing that looks at the composition of the butterflies’ wings for evidence of the types of plants they ate as caterpillars, said study co-author Dr. Megan Reich, a postdoctoral fellow at the University of Ottawa Ontario. With this method, the scientists concluded that the butterfly’s birthplace was either in Western Europe, North Africa or West Africa, she added.

The scientists concluded that the butterflies' birthplace was either in Western Europe, North Africa or West Africa using isotope tracing that looks at the composition of the butterflies' wings for evidence of the types of plants they ate as caterpillars.

But the real key to finding the path the butterflies took was a method first described in a September 2018 study led by Talavera that found that pollen stuck to butterflies can tell about their migratory journey through plants with it. which they fed. Butterflies observed in October 2013 had pollen from two West African plants, Guiera senegalensis and Ziziphus spina-christi. The tropical shrubs flower between August and November, according to the study, and this flowering season matches the time frame of the butterflies that Talavera discovered in South America.

Additionally, an analysis of weather data from the 48 hours before the beach butterflies were discovered showed it was “extremely favorable for the butterflies to disperse across the Atlantic from West Africa,” the study authors noted.

If the insects traveled from their likely birthplace of Europe, then to Africa and South America, the butterflies’ journey could be 4,350 miles (7,000 kilometers) or more.

“A lot of people think of butterflies as really fragile creatures. I think that really shows how strong and resilient they are and these amazing journeys that they go on – they really shouldn’t be underestimated,” Reich said.

The researchers hope to use the same techniques to investigate the migration patterns of other butterfly species, she added.

“This is just the first step in kind of a long process of trying to understand why this happened and how this happened,” Shockley said.

If future research reveals that the butterfly journey is likely to be a regular migration pattern, it is among the longest insect migrations in the world, he added.

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