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Painted lady butterflies venture far and wide with their impressive migratory patterns that span thousands of miles – but they often travel across land so they can stop for a rest.
Scientists have now found evidence that a group of winged travelers flew over the Atlantic Ocean for more than 2,600 miles (about 4,200 kilometers) 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, encountered about a dozen painted butterflies, known scientifically as Vanessa cardui, on a beach in French Guiana in October 2013. The insects, which are not typically found in South America, were worn with 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 with the Spanish National Research Council at the Botanical Institute in Barcelona. “The only explanation that came to mind was that they were long-distance migrants. »
But crossing an entire ocean was a novel experience for butterflies, even for those as worldly as lady-in-laws. Talavera and his colleagues had to eliminate a few factors before concluding that these butterflies had accomplished what was previously thought impossible.
An October 2016 study co-authored by Talavera found that painted butterflies migrate long distances (about 2,500 miles) to sub-Saharan Africa, overcoming obstacles like the Mediterranean Sea and the Sahara Desert. But despite this, the butterflies mostly stay on land where they can “stop and refuel, feed on flowers and then get the energy to keep going,” Talavera said.
According to the new study, the Atlantic crossing would take a painted lady five to eight days, depending on several variables.
Based on analyses of energy constraints, the researchers concluded that the butterflies could fly a maximum of 780 kilometers without stopping, but it was favorable wind conditions that allowed them to complete this long journey, Talavera said.
“It’s actually kind of a record for an insect, 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 monitors the evolving situation. migratory routes of insects.
There have been other cases in which experts suspect that butterflies and other migratory insects are traveling longer distances than usual, appearing on boats, isolated islands or countries where they are not usually found, Talavera said.
Researchers believe these butterflies took part in their annual migration to southern Europe, but got lost when the wind carried them into the ocean, he added. The butterflies then likely survived the trade winds, which blow from east to west near the equator, until they reached land in South America.
“Being suspended in the air column at the right height to enjoy the trade winds is simply remarkable,” said Dr. Floyd Shockley, collections manager in 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 displaced butterflies, compared to a single occasional butterfly found likely caught in storms, could be enough evidence that this was a coordinated migratory event for the group of insects, Shockley said .
The researchers took some crucial steps to confirm that these displaced butterflies actually crossed the ocean.
To rule out that the insects had not traveled overland from North America, the researchers analyzed their DNA and found that it matched that of European and African populations. Next, the team used a technique known as isotope tracing that examines the composition of the butterflies’ wings to find evidence of the types of plants they ate when they were caterpillars, said the co-author of the paper. study, Dr. Megan Reich, a postdoctoral researcher at the University of Ottawa in Ontario. Using this method, scientists concluded that the butterflies’ birthplace was either in Western Europe, North Africa or West Africa, she added.
But the real key to discovering the path butterflies take is a method first described in a September 2018 study led by Talavera, which found that pollen clinging to butterflies may be indicative of their migratory journey through plants which they feed on. The butterflies spotted in October 2013 had pollen from two West African plants, Guiera senegalensis and Ziziphus spina-christi. According to the study, these tropical shrubs bloom from August to November, and this flowering 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 was found to be “exceptionally favorable for the dispersal of butterflies across the Atlantic from West Africa,” the authors note in the ‘study.
If the insects had traveled from their likely birthplace, Europe, and then to Africa and South America, the butterflies’ journey could have included 4,350 miles (7,000 kilometers) or more.
“Many people consider butterflies to be very fragile creatures. I think it really shows how strong and resilient they are and the incredible journeys they take – they really shouldn’t be underestimated,” Reich said.
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 to understand why and how this happened,” Shockley said.
If future research reveals that the butterflies’ journey is likely a regular migration pattern, it would be one of the longest insect migrations in the world, he added.