Spanish researchers say that painted lady butterflies complete what is believed to be the longest one-way migration among all butterfly species, traveling from southern Europe, across the Sahara, and all the way to tropical Africa, a distance of roughly 3,700 miles.
That feat surpasses the one-way migrations of North America’s monarch butterflies, which travel as far as 3,000 miles in late summer from Canada and the U.S. to the Mexican highlands.
However, monarch butterflies, like birds, complete an annual round-trip migration, whereas painted lady butterflies are believed to stay in Africa and not return to the Mediterranean. The painted lady’s offspring return to southern Europe, which means that the species’ annual inter-generational migration covers nearly 7,500 miles, with two trips across the Sahara, Spanish scientists say.
Reporting in the journal, Biology Letters, the researchers said that by analyzing the stable hydrogen isotopes in the wings of adult butterflies, they could determine where the insects had developed as caterpillars. The plants that the butterflies fed on as caterpillars carry an isotope signature that enabled researchers to conclude that the insects had wintered in tropical Africa.