For decades, naturalists have debated whether the offspring of these immigrants ever make a southwards return migration. Research suggests that British painted ladies do undertake an autumn migration, making 14,500 km (9,000 mi) round trip from tropical Africa to the Arctic Circle in a series of steps by up to six successive generations.
The Radar Entomology Unit at Rothamsted Research provided evidence that autumn migrations take place at high altitude, which explains why these migrations are seldom witnessed. In recent years, thanks to the activity of The Worldwide Painted Lady Migration citizen science project, led by the Barcelona-based Institute of Evolutionary Biology (Catalan: Institut de Biologia Evolutiva), the huge range of migration has begun to be revealed. For example, some butterflies migrated from Iceland to the Sahara desert, and even further south.
