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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 (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 author of the study, Dr. Gerard Talavera, came across about ten painted lady butterflies, known by the scientific name Vanessa cardui, on a beach in French Guiana in October 2013 . are not usually found in South America, were worn with holes and cracks 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.
An October 2016 study that Talavera co-authored found that painted ladies migrate from Europe over vast 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. Still, the butterflies mostly stay over land, where they “can stop and refuel, feed on flowers and then get energy to keep going,” Talavera said.
According to the new study, crossing the Atlantic Ocean would take five to eight days, depending on different variables.
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, especially a butterfly, to perform 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 shows the migration routes of the insects.
There have also been cases where experts suspect that butterflies and other migratory insects travel longer distances than normal and end up on boats, remote islands or in countries where they are not normally 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.
“Being suspended at just the right height in the air column to take advantage of the trade winds is nothing short of remarkable,” says 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 just never documented it because we weren’t looking for it in South America?”
The discovery of about 10 butterflies that were not in the right place, as opposed to the single butterfly discovered that was likely swept away by a storm, could be evidence enough that this was a coordinated migration event for the insect group, Shockley said.
Researchers have taken some crucial steps to confirm that these out-of-place butterflies really did 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.
But the real key to finding the route the butterflies took was a method first described in a September 2018 study led by Talavera, which found that pollen clinging to butterflies can reveal something about their migration by the plants on which they fed. The butterflies spotted in October 2013 had the pollen of two West African plants, Guiera senegalensis and Ziziphus spina-christi. According to the research, the tropical shrubs bloom in August and November, and this blooming season matches the timeline of the butterflies Talavera discovered in South America.
Additionally, an analysis of weather data from 48 hours before the discovery of the stranded butterflies showed “exceptionally favorable conditions for the butterflies to disperse across the Atlantic Ocean from West Africa,” the authors noted in the study.
If the insects had traveled from their likely birthplace in Europe and then to Africa and South America, the butterflies’ journey could have taken 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 the amazing journeys 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 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 would be one of the longest insect migrations in the world, he added.