Millions of migratory painted lady butterflies have arrived in the UK to breed, triggering a rare biological event known as a "painted lady summer." Conservationists report that unusually warm spring temperatures across Europe have fueled this massive influx of insects.
A surge that could dwarf the 420 ,000 sightings of 2019
The current influx of painted lady butterflies is showing signs of being one of the largest in history . According to the charity Butterfly Conservation, the numbers seen so far this year have already significantly surpassed the totals from the previous year, where only 15,856 painted ladies were reported during the annual count. This suggests the current event could surpass the 2019 "painted lady summer," which saw more than 420,000 sightings.
If the trend continues over the coming weeks, Butterfly Conservation believes this year is on track to be the third-best year for painted lady numbers on record, trailing only the massive peaks seen in 1996 and 2009. professor Richard Fox, the head of science at Butterfly Conservation, described the inter-continental migration as a "wonder of the natural world," noitng that the distinctive orange, black, and white patterned wings of the species make them a favorite for the British public.
The multi-generational trek from sub-Saharan Africa
The arrival of these butterflies in the UK is the culmination of one of the longest insect journeys on Earth. As reported by Butterfly Conservation, the migration from sub-Saharan Africa to Europe is not completed by a single insect but by successive generations. Adults born in sub-Saharan Africa during the winter first fly to North Africa to mate and lay eggs.
Their offspring then undertake the crossing of the Mediterranean Sea into Southern Europe, where they again mate and lay eggs. It is the subsequent generation, born in Southern Europe, that arrives in the UK in late spring. These migrants have since laid their own eggs, meaning a new generation of "home grown" painted lady adults is currently emerging across the British countryside.
The mystery behind the boom-and-bust cycles of the painted lady
While the immediate cause of this year's surge is linked to recent heatawves providing ideal migratory conditions, the underlying drivers of these events remain elusive. Butterfly Conservation states that why the UK experiences these specific "painted lady summers" is not entirely understood, though they are clearly tied to breeding success in Africa and Southern Europe earlier in the year.
These insects typically follow boom-and-bust cycles influenced by predator numbers and the availability of food. In the UK, the boom years provide a natural ecological service, as painted lady caterpillars feed primarily on thistles, helping to manage the spread of domineering creeping thistle plants. However, the exact tipping point that turns a standard migration into a million-strong "summer" remains a point of scientific inquiry.
The Big Butterfly Count's August 9 deadline
To better understand these population spikes, Kate Merry,head of engagement at Butterfly Conservation, is encouraging the public to participate in the Big Butterfly Count. The initiative asks volunteers to spend 15 minutes in a sunny outdoor spot—such as a park or garden—to record their sightings. This citizen-science data is critical for experts to assess the annual health of butterfly populations.
The current counting window remains open until Sunday, August 9. Participants can report their findings via the Big Butterfly Count app or the organization's official website, providing the raw data needed to determine if this year will indeed enter the record books alongside 1996 and 2009.
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