The world’s biggest insect monitoring scheme is marking 50 years of butterfly data collection, with over 44 million records received from 782,000 volunteers during this time.
The UK Butterfly Monitoring Scheme (UKBMS) is jointly run by Butterfly Conservation, the UK Centre for Ecology & Hydrology (UKCEH), British Trust for Ornithology (BTO) and the Joint Nature Conservation Committee (JNCC).
The data have revealed that species – particularly those relying on specialist habitats – are disappearing from parts of the UK. This is due to habitat loss, pollution and climate change.
The newly published UKBMS annual results show that 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.
Contrasting fortunes
Data from the past 50 years show that overall, of the 59 native butterfly species monitored, 33 have declined, 25 have improved and one has insufficient data.
Adaptable species which can breed in farmland, parks and gardens are coping and some warm-loving species are even spreading to new areas due to climate change. For example, numbers of the Red Admiral – formerly just a summer visitor but now seen throughout the year – have rocketed by 330 per cent since 1976.
But specialist butterflies – which are restricted to particular habitats such as woodland glades or chalk downland – have fared worse including:
- Pearl-bordered Fritillary – down 70% since 1976. Its caterpillars almost exclusively feed on violet leaves
- The White-letter Hairstreak – down 80%. This butterfly lays its eggs on elm trees which have been devastated by disease in recent decades.
- Grayling – down 72%. Its typical habitats - sparsely vegetated, sunny areas – have declined.
Small Tortoiseshell, a garden favourite has declined even though it is a generalist species, with numbers down 87% since 1976.
Meanwhile, numbers of the Large Blue have soared after the species, previously extinct in Britain, was successfully reintroduced in this country in 1979 by UKCEH and partners.
Other specialist species to do well thanks to conservation efforts include the Black Hairstreak, whose numbers have increased by 844 per cent since 1995, and Silver-studded Blue (up 76% since 1979).
Invaluable dataset
Dr Marc Botham, Butterfly Ecologist at UKCEH, said: "Butterfly numbers naturally fluctuate from year to year depending on the weather, which is why the UK Butterfly Monitoring Scheme is so important. This invaluable long-term dataset, based on surveys by dedicated volunteers, enables scientists to assess what is actually happening in the countryside over time.
“Data from the past 50 years show many butterflies are in long-term decline, and knowing which species are struggling and where informs conservation action to support populations."
Records have been collected by citizen scientists who carry out weekly counts of butterflies along defined transects on days with suitable weather criteria from April to September. These volunteers have walked a total of more than 1.5 million kilometres since 1976 at more than 7,600 sites to produce the incredible dataset. That’s the equivalent of walking 40 times around the world – or to the moon and back twice.
The UKBMS also includes butterfly counts from randomly selected Wider Countryside Butterfly Survey squares and targeted species surveys.
The individual species trends for butterflies contribute to UK and country level composite species indicators – for example the UK biodiversity indicator on butterflies in the wider countryside.
For more information go to www.ukbms.org
UKCEH involvement is funded by National Capability for UK Challenges (NC-UK)