How a group of butterflies flew 4,200 kilometers across the Atlantic Ocean without stopping

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Painted butterflies venture far and wide with their stunning migratory patterns that span thousands of miles – but they often travel by 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 on 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, found 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 normally found in South America, were worn out, with holes and tears in their wings.

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

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

How far can a butterfly fly

One October 2016 Study which Talavera co-authored, found that painted women from Europe migrate great distances 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 then, butterflies mostly stay on land, where they can “stop and refuel, feed on flowers and then get energy to keep going,” Talavera said.

Crossing the Atlantic would take a painted butterfly five to eight days, depending on different variables, according to the new study.

Based on analyzes of energetic constraints, the researchers concluded that the butterflies could fly a maximum of 780 kilometers without stopping, but favorable wind conditions were 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 stopping,” said Talavera, who also leads the Worldwide Painted Lady Migration Project, a global citizen science project that tracks the migratory routes of insects.

There have been other cases in which experts suspect that butterflies and other migratory insects travel greater distances than usual, appearing on boats, remote islands or countries where they are not normally found, Talavera said.

Researchers believe these butterflies took part in their annual migration to southern Europe, but were lost when the wind blew them into the ocean, he added. The butterflies then probably faced the trade winds, which blow from east to west near the equatoruntil they reached lands in South America.

“Being suspended in the air column at just the right height to take advantage of the trade winds is nothing short of 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 raises the question: Have they been doing this for a long time and we never documented it because we weren’t looking in South America?”

The discovery of about 10 out-of-place butterflies, compared with the occasional discovery of a single chick that was likely caught in storms, could be enough evidence that this was a coordinated migratory event for the group of insects, Shockley said.

Tracking a butterfly

Researchers took some crucial steps to confirm that these displaced butterflies actually traveled across the ocean.

First, to rule out that the insects had not traveled 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 tracking, which analyzes the composition of 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 U.S. from Ottawa in Ontario. Through this method, scientists concluded that the birthplace of the butterflies was in Western Europe, North Africa or West Africa, she added.

But the real key to finding the route the butterflies followed was a method first described in a book. September 2018 Study led by Talavera who discovered that pollen clinging to butterflies could reveal their migratory journey through the plants they fed on. The butterflies spotted in October 2013 contained pollen from two West African plants, Guiera senegalensis and Ziziphus spina-christi. The tropical shrubs bloom between August and November, according to the study, and this flowering time coincides with the timeline of the butterflies Talavera discovered in South America.

Furthermore, an analysis of meteorological data from 48 hours before the discovery of the stranded butterflies showed it to be “exceptionally favorable for butterflies to disperse across the Atlantic from West Africa,” the authors noted in the study.

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

“Many people think of butterflies as really fragile creatures. I think it really shows how strong and resilient they are and the incredible 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, he added.

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

If future research finds that the butterflies’ journey is likely a regular migration pattern, it would be among the longest insect migrations in the world, he added.

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