An extraordinary dataset of over 44 million records from 782,000 volunteer has revealed what has happened to the UK's butterflies as the national landscape has changed over the past 50 years.
Citizen scientists have walked more than 1.5 million kilometres since 1976 at more than 7,600 sites to produce the incredible UK Butterfly Monitoring Scheme (UKBMS) dataset. That’s the equivalent of walking 40 times around the world – or to the moon and back twice.
Of the 59 native butterfly species monitored, 33 have declined, 25 have improved and one mountain-dwelling species has insufficient data.
While some species are coping and even spreading to new areas, other butterflies, sometimes those restricted to particular habitats such as woodland glades or chalk downland, have fared worse – and many are declining at alarming rates.
The Pearl-bordered Fritillary, a striking orange-and-black butterfly whose caterpillars only eat violets growing in warm, sunny spots in woodland clearings and bracken-covered hillsides, has declined by 70 per cent since 1976.
Some habitat specialists, such as the heathland-dwelling Silver-studded Blue, have bucked the trend, thanks to intensive conservation efforts.
Habitat generalist butterflies also show a mix of fortunes, with some increasing but others such as the Small Tortoiseshell having declined by 87 per cent.
UKBMS is jointly run by Butterfly Conservation, the UK Centre for Ecology & Hydrology (UKCEH), British Trust for Ornithology (BTO) and JNCC. Volunteers have been counting butterflies across the country since 1976 and is now marking its 50th anniversary with this concerning set of results.
The White-letter Hairstreak is another charismatic specialist which has suffered massive declines: adults have striking wing patterns and the caterpillars glow in the dark under UV light, however females only lay their eggs on elm trees, millions of which have died from Dutch Elm Disease. The White-letter Hairstreak has declined by 80 per cent since 1976.
Among the habitat generalist species that have done well is the Red Admiral, which has rocketed by 330 per cent since 1976. It was once a summer visitor to the UK but as the climate has warmed it is now seen here year-round. With caterpillars that feed almost exclusively on stinging nettles, they are able to survive in many habitats.
Some specialist species have done well, such as the Black Hairstreak, which only lays its eggs on blackthorn but has increased by 844 per cent since 1995 – however this is a species which Butterfly Conservation has been doing targeted work to help across the country for decades.
The largest increase of any species is the Large Blue, whose numbers have soared by 1,866 per cent since 1983 – but that's because, after being declared extinct in Britain in 1979, the butterfly has been successfully reintroduced.
Elsewhere across the country, Butterfly Conservation and partners have done targeted conservation work which has successful slowed the decline of rare species and increased local populations.
The UKBMS results for last year in particular highlight the scale of the challenge: despite the UK experiencing its sunniest year on record – weather in which butterflies should thrive – 2025 was only an average butterfly year (20th out of the past 50 years), and not a single species recorded its best year.
This mirrors last year’s results of Butterfly Conservation's Big Butterfly Count, which saw record participation of more than 125,000 people but produced only average numbers of butterflies per count.
The UK Butterfly Monitoring Scheme is just one of JNCC’s 11 schemes that monitor species throughout the UK. These monitoring schemes provide the evidence base that underpins effective conservation action. They are critical to helping us understand how nature is faring and whether policies impacting conservation are being successful. These insights on the impact of policies on species, combined with other monitoring data, will also enable us to project the likely impact of conservation polices and their effectiveness.
Steve Wilkinson, Director of Ecosystem Evidence & Advice at JNCC, said: "Reaching 50 years of continuous butterfly monitoring data is a remarkable milestone which would not have been possible without the extraordinary dedication of our volunteers. Their consistent and careful work, year after year, has built an evidence base that is unmatched anywhere in the world for insect monitoring.
“This half-century of data gives us an invaluable window into what is working and what is not – from the spectacular recovery of the Large Blue following reintroduction, to the devastating declines of specialists like the Pearl-bordered Fritillary. Without this evidence timeline, we would be flying blind. Understanding where conservation efforts are making a real difference and where we need to strengthen efforts, depends entirely on the quality and continuity of data that our volunteers make possible.”
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