How a Group of Butterflies Flew 2,600 Miles Across the Atlantic Ocean Without Stopping

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Painted Ladies travel far with their impressive migration patterns that span thousands of kilometres. However, they often travel over land so they can stop to rest.

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

The discovery ends a decade-long mystery that began when entomologist and lead author of the study Dr. Gerard Talavera came across about 10 Painted Ladies, known by the scientific name Vanessa cardui, on a beach in French Guiana in October 2013. The insects, which are not normally found in South America, were worn out and had holes and tears in their wings.

“They looked exhausted. They couldn’t even fly much — they were jumping instead of flying,” said Talavera, a senior researcher for the Spanish National Research Council at the Botanical Institute of Barcelona. “The only explanation that came to mind was that these were long-distance migrants.”

But crossing an entire ocean was unheard of for butterflies, even ones as worldly as Painted Ladies. Talavera and his colleagues had to rule out a few factors before concluding that these butterflies had accomplished what had previously been thought impossible.

How far a butterfly can fly

An October 2016 study that Talavera worked on found that Painted Ladies from Europe migrate long distances of about 2,500 miles (about 4,000 kilometers) to sub-Saharan Africa, encountering obstacles such as the Mediterranean Sea and the Sahara Desert. But even then, the butterflies stay primarily on land, where they “can stop and refuel, feed on flowers and then get energy to keep going,” Talavera said.

It could take a Painted Lady butterfly five to eight days to cross the Atlantic Ocean, depending on several variables, according to new research.

Based on analyses of energy constraints, researchers concluded that the butterflies could fly up to 780 kilometers (480 miles) nonstop, but that favorable wind conditions allowed them to make the long journey, Talavera said.

“This is actually a record for an insect, and especially a butterfly, to make such a long flight without the ability to stop,” said Talavera, who also directs the Worldwide Painted Lady Migration Project, a global citizen science project that maps the insects’ migration routes.

There are also cases where experts suspect butterflies and other migratory insects are traveling longer distances than normal and ending up on boats, remote islands or in countries where they would not normally be found, Talavera said.

The researchers believe these butterflies were making their annual southward migration from Europe but got lost when winds blew them out to sea, he added. The butterflies then likely rode the trade winds, which blow east to west near the equator, until they reached land in South America.

“It’s just remarkable to be hanging at just the right height in the air column to take advantage of the trade winds,” said Dr. Floyd Shockley, collections manager in the entomology department at the Smithsonian National Museum of Natural History in Washington, D.C., who was not part of the new study. “It 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 that were out of place, as opposed to the single butterfly found that was likely swept away by storms, could be evidence enough that this was a coordinated migration event for the insect group, Shockley said.

Following a butterfly

Researchers have taken several important steps to confirm that these butterflies did indeed travel across the ocean.

First, to rule out that the insects didn’t travel overland from North America, the researchers analyzed their DNA and found that it matched that of European-African populations. The team then used a technique known as isotope tracing, which looks at the composition of the butterflies’ wings to find evidence of the types of plants they ate as caterpillars, said study co-author Dr. Megan Reich, a postdoctoral researcher at the University of Ottawa in Ontario. Using this method, the scientists concluded that the butterflies’ birthplace was in Western Europe, North Africa or West Africa, she added.

Scientists concluded that the butterflies' birthplace is in Western Europe, North Africa or West Africa by using isotope studies, which look at the composition of the butterflies' wings to find evidence of the types of plants they ate as caterpillars. - Gerard Talavera

Scientists concluded that the butterflies’ birthplace is in Western Europe, North Africa or West Africa by using isotope studies, which look at the composition of the butterflies’ wings to find evidence of the types of plants they ate as caterpillars. – Gerard Talavera

But the real key to finding the path the butterflies took was a method first described in a September 2018 study led by Talavera, who found that pollen stuck to butterflies can reveal information about their migratory paths through the plants they feed on. The butterflies spotted in October 2013 had pollen from two West African plants, Guiera senegalensis and Ziziphus spina-christi. The tropical shrubs bloom in August and November, the study says, and that blooming season matches the timeline of the butterflies Talavera discovered in South America.

Furthermore, an analysis of weather data from the 48 hours before the discovery of the stranded butterflies showed that it was “exceptionally favorable for the dispersal of the butterflies across the Atlantic Ocean from West Africa,” the authors noted in the study.

If the insects traveled from their likely birthplace in Europe to Africa and South America, the butterflies’ journey could be 7,000 kilometers or more.

“A lot of people think of butterflies as very fragile creatures. I think this 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 study the migration patterns of other butterfly species, she added.

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

If future research shows that the butterflies’ journey is likely a regular migration pattern, it will be one of the longest insect migrations in the world, he added.

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