The painted lady is one of the most ordinary butterflies in the world: orange, black and white, found on almost every continent (sources disagree on whether the exception besides Antarctica is South America or Australia; it’s at least rare in both). Its Latin name is Vanessa cardui, which Linnaeus gave it in 1758, and the second half means “of the thistle”. Its caterpillars eat all sorts of things (more than a hundred host plants have been recorded), but thistles, Carduus and Cirsium, are the ones it’s named for. In some places it’s simply called the thistle butterfly.

I went looking for it because of the name. I stayed because of where it goes.

A loop no one flies

Every spring painted ladies come north out of Africa into Europe. Some reach Britain, Scandinavia, and past the Arctic Circle. Every autumn they go back south, across the Mediterranean and the Sahara, to the savannah on the far side. Counted as a single loop, it’s somewhere around 12,000 to 14,500 km a year, depending on whose estimate you use. That’s the longest known migration of any butterfly.

No butterfly flies it. An adult painted lady lives a few weeks. The loop is carried by something like six generations in a row: one lays eggs on a thistle in Morocco, its offspring push on to Spain or France, theirs to Britain, and so on, then the late-summer ones turn round. The ones that arrive in the Sahel in autumn have never been there, and neither had their parents. None of them is shown the way. What gets passed on isn’t a route or a memory. It’s a built-in preference for a direction, which flips between spring and autumn. Lab work suggests they hold that heading with a sun compass. Everything else, each generation meets for the first time.

The return nobody saw

For a long time the autumn half looked as if it didn’t happen. People saw painted ladies arrive in Britain every spring, sometimes in huge numbers, and then they just thinned out. There was no visible southbound stream. The obvious reading was that the northern generations were a dead end: they bred, and their offspring died in the cold.

In 2009 there was a big painted lady year, and a group led by Constantí Stefanescu, with the Rothamsted radar team under Jason Chapman, looked properly. They combined more than 60,000 public sightings from across Europe with a vertical-looking radar in Hampshire that can count individual insects passing overhead. It estimated about 11 million painted ladies coming into Britain that spring and about 26 million leaving in autumn. The leaving ones were the part nobody had seen, because they went high, mostly 200–400 m up and sometimes over a kilometre, where the wind can carry them at close to 100 km/h. The paper came out in Ecography in 2013. The return had always been there. It was just above eye level.

Ten on a beach

In October 2013, the entomologist Gerard Talavera found about ten painted ladies on an Atlantic beach in French Guiana. They shouldn’t have been there. The species isn’t normally found in South America, and these were worn out, their wings torn and holed.

It took over ten years to work out where they came from. His group sequenced their genomes, which tied them to the Europe–Africa population rather than the North American one. Isotopes in their wings, laid down when they grew as caterpillars, pointed to a birthplace in western Europe. And pollen still stuck to them came from two plants, Guiera senegalensis and Ziziphus spina-christi, that grow in tropical Africa and flower at the end of the West African rainy season. So they’d fed in West Africa, and wind modelling for the days before they were found showed winds unusually well set to push something from there out over the ocean.

Put together, that’s at least 4,200 km across the Atlantic, non-stop, in something like five to eight days. From where they were born, the whole trip may have been 7,000 km or more. The study (Suchan, Talavera and others, Nature Communications, 2024) calls it potentially the first verified crossing of the Atlantic by an insect. It’s only possible with the wind doing most of the work. A painted lady can’t carry enough fuel to flap that far.

I don’t know what happened to those ten. The paper doesn’t say they founded anything, and I’d guess they didn’t. I keep thinking about them anyway. They did the one thing a painted lady does, going where the wind’s going and trusting there’ll be a thistle at the other end. For once, it went further than anyone thought it could.

Sources (abstracts and write-ups; I haven’t read the full papers): Stefanescu et al., “Multi-generational long-distance migration of insects: studying the painted lady butterfly in the Western Palaearctic”, Ecography 2013; Suchan et al., “A trans-oceanic flight of over 4,200 km by painted lady butterflies”, Nature Communications 2024; Talavera et al. on the Sahara crossing, Biology Letters 2016; University of York and Butterfly Conservation write-ups of the 2009 radar study; CNN and Smithsonian coverage of the 2024 paper for the pollen species and the “about ten butterflies, worn out” detail.