The UK is experiencing a rare surge in painted lady butterflies this summer, with conservationists describing it as a once-in-a-decade event. Butterfly Conservation, a wildlife charity leading monitoring efforts, has reported that unusually warm weather across Europe this spring triggered a large influx of these migratory insects, prompting what is being called a “painted lady summer.”

Painted lady butterflies (Vanessa cardui) are known for their distinctive orange, black, and white patterned wings. Their migratory journey spans thousands of miles, originating from sub-Saharan Africa and progressing through successive generations as they travel northward into Europe, with the UK as a key breeding destination along the way. The butterflies complete their life cycle in five to eight weeks, meaning it can take up to six generations for the species to complete the full annual migration.

While this migration occurs every year, environmental conditions such as favorable weather and ample food availability lead to periodic population booms roughly once a decade. The current year, 2026, is projected to be the third highest for painted lady numbers on record, following notable peaks in 1996 and 2009. Butterfly Conservation noted that counts of painted ladies this year have already surpassed those recorded at the same time in both 2019—a previous painted lady summer that saw more than 420,000 butterflies reported—and last year, when just under 16,000 were recorded.

Professor Richard Fox, head of science at Butterfly Conservation, highlighted the significance of the migration as one of the longest insect journeys in the world and expressed enthusiasm about the ongoing population surge. “The numbers we’re seeing have already dwarfed last year’s total,” he said. “We are absolutely delighted.” He added that the emergence of a new generation of butterflies across the UK is a key part of the species’ continuing migration.

The charity is urging the public to participate in its annual Big Butterfly Count, a citizen science project that collects data on butterfly populations to help track their health and abundance over time. Observers are encouraged to report sightings of painted ladies as well as other butterfly species through the official website.

The influx has been noticeable across various parts of the UK, where large groups of painted ladies have been observed feeding and mating. This natural phenomenon not only provides a spectacular visual display but also serves as an important ecological indicator as experts continue to study the impacts of climate and environmental changes on migratory insects.