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Over the past fifty years, the rise in warmer and sunnier weather—partly influenced by climate change—has benefited certain butterfly species across the UK, according to data from one of the world’s most extensive insect monitoring projects. However, despite these positive trends among some butterflies, the overall situation remains concerning as many native species are experiencing substantial declines.
The UK Butterfly Monitoring Scheme (UKBMS) has collected an impressive 44 million records from nearly 782,000 volunteer surveys since 1976. This long-term citizen science initiative tracks 59 native butterfly species, of which 33 have decreased in population, 25 have shown increases, and one mountain species lacks sufficient data for assessment. Species such as the Red admiral have adapted well, with some now overwintering in the UK due to milder conditions. Meanwhile, Comma butterflies have rebounded since monitoring began, and Orange tip butterflies have grown by over 40% since 1976. Conservation initiatives have also supported the recovery of the rare Black hairstreak and the Large Blue butterfly, which was considered extinct until efforts helped revive its numbers.
Butterfly Conservation, the charity involved with the monitoring, notes a clear divide between species that adapt easily to different environments and those specialized to particular habitats. Butterflies thriving in diverse locations such as farmland, parks, and gardens tend to be increasing, with climate change extending their breeding seasons and expanding their ranges northward. Prof Jane Hill from the University of York emphasizes the exceptional value of the data collected, highlighting that as cold-blooded insects, butterflies generally benefit from warmer temperatures and have opportunities to move further north within the UK. Conversely, species dependent on specialized habitats like woodland clearings or chalk grasslands are facing severe declines due to habitat pressures and a lack of suitable new areas to colonize.
Some species have suffered dramatic losses; the white-letter hairstreak population has fallen by 80%, while the pearl-bordered fritillary—whose caterpillars feed exclusively on violets—has dropped by 70%. Even adaptable butterflies such as the small tortoiseshell have seen significant decreases, with its numbers plunging by 87%. Prof Richard Fox, head of science at Butterfly Conservation, remarks on the loss of diversity within butterfly communities, drawing a parallel with the disappearance of family-run shops and traditional skills from British high streets in the face of environmental degradation and simplified landscapes.
The success of the UKBMS is due to a remarkable volunteer effort, with participants collectively walking more than 932,000 miles at over 7,600 sites. Steve Wilkinson, director of the Joint Nature Conservation Committee, stresses the importance of this extensive data collection, stating, “Without this evidence timeline, we would be flying blind.” This comprehensive dataset informs conservation priorities and guides efforts, particularly as many butterflies are highly selective about their food plants. Certain species rely on just one or two specific plants; for example, the Duke of Burgundy depends on primroses and cowslips, while the purple emperor feeds on goat or grey willow.
To address these challenges, Butterfly Conservation manages reserves like Magdalen Hill Downs, which support a broad variety of habitats and native plants. Reserves officer Fiona Scully points to the diversity of flora on the chalky fields—including cowslips, lady’s bedstraw, toadflax, betony, scabious, and knapweed—as key to sustaining strong butterfly populations. Despite 2025 being the sunniest year on record in the UK—a condition generally favorable to butterflies—the monitoring data recorded only average butterfly numbers, placing it 20th in the past 50 years with no species achieving their best population years. This trend aligns with findings from Butterfly Conservation’s Big Butterfly Count, which, despite record public engagement, also reported average butterfly activity across the UK
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