Britain sees second-best butterfly season in 16 years; people counted almost 1.4 million common butterflies and moths; painted ladies jumped by 335%, but scientists are worried

Butterfly boom may come at a cost

So what brought the butterfly boom? Adult butterflies want sunshine and dryness. They got both, in abundance. The five-heatwave season turned out to be perfect for feeding and mating. The significant surge also grabbed human attention. Migratory species like painted ladies rode favourable winds and found conditions ideal for breeding. In pure adult butterfly terms, the weather delivered. But experts believe that the boom may have simultaneously seeded a population crash for next year. Adult butterflies appreciate the bright summer, but for the caterpillars, it’s not really promising. The grass, wildflowers and other plants that caterpillars eat withered in the drought.“Adult butterflies love hot, sunny weather for flying, feeding and breeding, and that’s exactly why people saw so many this summer. But a good summer for adult butterflies is not the same as a good summer for butterfly populations,” Richard Fox, head of science at Butterfly Conservation, told The Guardian.“What matters far more is what’s happening on the ground, to the butterflies’ caterpillar offspring and the plants they depend on. The very same weather that made it a good year for butterflies – lots of sunshine and very little rain – could mean we’re actually on course for a population crash, which could take years to recover from.”

But no two droughts are the same. Matthew Oates, an independent naturalist who has kept meticulous butterfly diaries since 1964, pointed to the difference. The 1976 drought was brutal for butterflies, partly because it followed a year of already-dry weather, priming plants to fail catastrophically. This summer was different. Winter 2025 was wet, and early June saw significant rainfall before the drought kicked in. These conditions may have given butterfly foodplants enough water during critical growth stages. He said he was hopeful that last year’s wet winter and wet week in early June might prevent the population crash next year.Though it has been a strong summer for migratory butterflies, drought-sensitive species struggled. The speckled wood, green-veined white and ringlet were all recorded in below-average numbers during the Big Butterfly Count, with declines of 44%, 54% and 39%, respectively, since 2011.Fox thinks there are winners and losers in hotter summers: “There will be very few butterfly species that can thrive in the drought situations we had this summer across much of the UK.”Both experts noted that Britain is entering unknown territory in terms of how climate extremes would impact native wildlife and flying insect populations.“If we get another summer of drought or excessive heat that’s really moving into a new future for us and our wildlife, including butterflies,” Fox said.“These last two summers have been way beyond our previous experience. We are out of our comfort zone and we can’t speak with any confidence any more. A lot of our butterflies are behaving more like they behave much farther south in Europe. In some ways it is exciting, but I worry about how relevant our existing, treasured knowledge is. We need every entomologist we can get in this country,” Oates added.

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