Painted ladies are among the most widely distributed butterflies on Earth, and in the western Palaearctic they sustain a yearly circuit between breeding grounds south of the Sahara and as far north as Scandinavia and Iceland. The full loop is completed by a succession of generations rather than by individuals, with each leg exploiting seasonal flushes of larval host plants.
The southward return was long doubted because few butterflies were seen heading south at ground level. Entomological radar showed that autumn migrants fly high, often several hundred metres up, where they are effectively invisible to observers and can ride favourable winds. Stable hydrogen isotopes laid down in wing tissue during larval growth independently linked northern European individuals to natal areas far to the south.
Abundance swings enormously between years. Some seasons produce almost no arrivals in Britain, while irruption years bring millions, driven largely by rainfall and vegetation growth in North African and Middle Eastern breeding zones. Predicting these years remains imprecise.