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Painted butterflies travel far and wide in their spectacular migration patterns that stretch for thousands of miles – but they often travel overland, 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 finding ends a ten-year mystery that began when entomologist and lead study author Dr. Gerard Talavera came across about 10 painted 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 worn out with holes and tears in their wings.
“They looked exhausted. They couldn’t even really fly – they kind of jumped instead of flying,” said Talavera, a senior researcher for Spain’s National Research Council at the Institute of Botany in Barcelona. “The only explanation that came to my mind was that these were long-distance migrants.”
But butterflies crossing a whole sea were nothing to be heard of, even ones as mundane as the painted women. Talavera, along with his colleagues, had to rule out several factors before he came to the conclusion that these butterflies had achieved what was previously thought impossible.
How far can a butterfly fly
An October 2016 study coauthored by Talavera found that painted women from Europe travel a great distance of about 2,500 miles (about 4,000 kilometers) to sub-Saharan Africa, facing obstacles such as the Mediterranean Sea and the Sahara Desert. But even so, the butterflies mostly stay on land where they can “stop and refuel, feed on flowers and then get the energy to continue,” Talavera said.
Crossing the Atlantic would take a painted lady butterfly five to eight days, depending on various variables, according to the new study.
Based on analyzes of the energy constraints, the researchers concluded that the butterflies could fly a maximum of 485 miles (780 kilometers) or so without stopping, but favorable wind conditions allowed them to complete the long journey, which Talavera said.
“This is really a record for an insect, especially a butterfly, to fly that far without the possibility of stopping,” said Talavera, who also leads the Painted Women’s Worldwide Migration Project. a global citizen science project that tracks the migratory routes of insects.
There have been other cases where experts suspect butterflies and other migratory insects are traveling longer distances than usual, encountering boats, remote islands or countries where they are not normally found, Talavera said.
The 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 said. The butterflies then probably rode the trade winds, which blew east to west near the equator, until they reached land in South America.
“It’s not a great thing to be suspended in the air column at the right height to take advantage of the trade winds,” said Dr. Floyd Shockley, collections manager for the entomology department at the Smithsonian’s National Museum of Natural History in Washington, DC, 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 out of place, compared to the occasional single found caught in storms, could be enough evidence that this was a coordinated migration event for the group of insects, Shockley said.
Butterfly tracking
Researchers have taken several crucial steps to confirm that the butterflies traveled from here across the sea.
First, to prove that the insects did not travel overland from North America, the researchers analyzed their DNA, and found that it matched the European-African population. Next, the team used a technique called isotope tracking 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. in Ontario. In this way, the scientists determined that the birthplace of the butterfly was in Western Europe, North Africa or West Africa, she said.
But the real key to finding the route the butterflies took was a method first described in a September 2018 study led by Talavera that found that pollen that sticks to butterflies can tell about their migratory journey through the plants they fed on. The butterflies spotted in October 2013 had pollen from two West African plants, Guiera senegalensis and Ziziphus spina-christi. The tropical shrubs bloom through August and November, according to the study, and this blooming season coincides with timeline of butterflies discovered by Talavera in South America.
In addition, analysis of weather data from 48 hours before the beach butterflies were found showed that it was “extremely favorable for the butterflies to disperse across the Atlantic from West Africa,” the authors noted in the study.
If the insects traveled from their likely birthplace in Europe, then to Africa and South America, the butterflies’ journey could consist of 4,350 miles (7,000 kilometers) or more.
“Many people think of butterflies as very fragile creatures. I think this really shows how strong and resilient they are and the amazing journeys they make – they really shouldn’t be underestimated,” said Reich.
The researchers hope to use the same techniques to investigate the migration patterns of other butterfly species, she said.
“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 finds that the butterfly’s journey is likely to be a regular migration pattern, it will be among the longest insect migrations in the world, he said.
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