Butterflies are no strangers to long-haul flights. The Monarch butterfly, for example, is known to travel some 4800 kms from as far North as Canada in winter, to Mexico, before travelling back to the U.S. and Canada over the course of generations. These huge waves of butterflies typically light up weather radar. However none make trips across entire oceans.

“Vanessa Cardui”, the ‘Painted Lady” butterfly’s long distance migration is an epic journey by any standard. Defying all odds, this tiny insect crossed the ocean in a non stop flight. Now, an international team of scientists has documented this amazing journey and found that the butterflies can adjust their routes and timing based on weather patterns, resource availability and even human induced changes in the landscape.

This story actually began a decade earlier in 2013, when Gerard Talavera, a Spanish researcher from the Botanical Institute of Barcelona discovered Painted Lady butterflies along the beaches of French Guyana. This was far outside their native range, as they are not known to be living in South America. Three out of ten individuals were captured alive. Talavera noticed their worn-out wings with holes. Judging from their damaged wings and resting behaviour on the sands, it was apparent that they had arrived after a vigorous flight across the ocean.

The discovery spurred an investigation into how this butterfly, which only stretches a couple of inches, could be found so far from its usual home in Western Africa. The results of this decades long inquiry were published this week in the journal ‘Nature’ <https://www.nature.com/articles/s41467-024-49079-2>

“We usually see butterflies as symbols of the fragility of beauty, but science shows us that they can perform incredible feats," Roger Vila, a researcher at the Institute of Evolutionary Biology in Barcelona and co-author of the study, said in a press statement. “There is still much to discover about their capabilities.”

They have a five to nine-centimetre wingspan, the females laying about 500 eggs in their short 2-4 week lifespan after emerging from its cocoon. Breeding along the way, they take these little steps, a generation at a time. Although they can, they don't always make the migration in a single generation.

To put that in perspective, the best laying chicken breeds can only lay about 5-6 eggs per week. Although they’re fundamentally a different species, 500 butterfly eggs are still impressive for the lovely little lady.

During regular migration over land, the Painted Lady species travels a phenomenal 14000 km round trip from Africa to the Arctic Circle – almost double the length of the famous migrations undertaken by Monarch butterflies in North America. During this short life they find a mate, reproduce and lay eggs to start the life cycle all over again.

The whole journey is not undertaken by individual butterflies but is a series of steps by up to six successive generations so Painted Ladies returning to Africa in the autumn are several generations removed from their ancestors who left Africa earlier in the year.

The extent of the annual journey undertaken by the Painted Lady butterfly is astonishing. This tiny creature weighing less than a gram with a brain the size of a pinhead and no opportunity to learn from older, experienced individuals, undertakes an epic intercontinental migration in order to find plants for its caterpillars to eat. So when the next generation of Painted Ladies emerge, there may be far too few food plants left to sustain another generation of butterflies. The best alternative for the vast majority of them is to migrate outward from the source area to seek other areas with more abundant food for their offspring.

You've probably seen a painted lady (Vanessa cardui) butterfly at some point in your life. This orange-brown butterfly is one of the most common, widely distributed butterfly species, found on all continents of the world except Antarctica and Australia.

This particular ocean migration has startled one and all. After a decade of painstaking research work, scientists have now uncovered how these butterflies managed to cross the ocean - marking the first documented transoceanic flight by an insect. Further insights into this remarkable phenomenon can be found in the study.

The team confirmed this journey by analysing the molecular properties (DNA) of the pollen found on them, the nature of their wings and also maps of trade winds that make such a transatlantic journey possible. The findings strongly suggest that they came from West Africa or even farther away from Europe. The study also suggests that these butterflies could have been on their regular migration from Europe across the Sahara, but got swept off course due to strong winds.

This journey encompassed a minimum flight distance of 4200 km over the ocean, at an average altitude of 500 metres as known by radar records, and potentially exceeding 7000 km from the point of butterfly emergence. This means flying on an average of about 850 kms a day at about 35 km/hr, with top speeds of up to 48 km/hr. This is by any level of imagination, astonishing as it is over water and non stop.

"It's an amazing trip—the type of trip known to birds, but not insects," Talavera says.

Studying this butterfly’s migration is highly crucial to conservation efforts, because so little is known about insect migration in general, and painted ladies in particular. It's a highly mobile species and is vulnerable to threats like habitat loss, climate change and the use of pesticides. Imagine how many would have perished along the way? And yet they kept going. Imagine once again when they launched themselves one last time from a shrub along the coast of West Africa, looking into the hazy blue horizon ahead, with no perch for 4000 kms? Did they know? Did they consciously try to reach a destination across the ocean? They do it on the northern migratory land routes. They know the geography of our planet. This is truly incredible for a pinhead sized brain.

Understanding this migratory behaviour is not just a scientific curiosity but a vital tool to create strategies to protect this insect, and the ecosystem it supports. It is also an alarming wake up call to the possibility of climate change altering their habitats critically, endangering them and surely one day - all life.

We humans should seize the urgency of this issue. The humble tiny butterfly - ‘The Painted Lady'' has in fact painted and displayed an alarm banner for us to see - stretched across the planet.