Official statistic on Abundance of UK Butterflies
This page hosts the Official statistic on Abundance of UK Butterflies (2026 release; including data up to 2025), published on 27 March 2026.
Official Statistic Description
The statistic comprises population abundance trends of UK butterfly species based on results of the UK Butterfly Monitoring Scheme (UKBMS), and is published annually as an Official Statistics on JNCC’s website.
The UKBMS is a long-term monitoring scheme (running since 1976), involving repeat sampling at thousands of locations across the UK. The main method involves regularly counting butterflies along defined transects on days with specified weather criteria. The statistics incorporate data from three components of the UKBMS: traditional self-selected transects; stratified random Wider Countryside Butterfly Survey (WCBS) squares; and targeted species surveys (for example timed counts, larval web counts, and egg counts).
The UK Butterfly Monitoring Scheme is organised and funded by Butterfly Conservation (BC), the UK Centre for Ecology & Hydrology (UKCEH), the British Trust for Ornithology (BTO), and the Joint Nature Conservation Committee (JNCC). The UKBMS is indebted to all volunteers who contribute data to the scheme.
Scope of the statistic
These data cover butterfly species from the UK.
Population trends are presented at UK level for 58 of the 59 regularly occurring species, and at country level where sufficient data are available. It should be noted that the Channel Islands and the Isle of Man are included within the UK trend analysis. Long term trends and abundance indices of recorded species are presented for 1976–2025 for the UK, England, and Wales, 1979–2025 for Scotland, and 2004–2025 for Northern Ireland.
Short term trends are analysed for the UK and the four countries for the last ten years, 2016–2025.
More detail on approach and methods is available on the UKBMS website.
The 2025 summary of changes tables for the UK and at regional levels (England, Northern Ireland, Scotland, Wales) is available to download as an Excel spreadsheet. The tables includes trend estimates for 58 species regularly recorded in the UK and for which sufficient data are available at regional levels.
Summary of results
Annual changes
- Trends for UK butterflies can vary significantly from year to year, reflected in the differences between the 2024 and 2025 data. 2025 was an average year, ranking 20th out of 50 years of recording, with no species showing their worst results for the UK. In contrast, 2024 was the 4th worst year for butterfly abundance since the first year of the UKBMS, with 9 species showing their worst year on record.
- Some species have had marked successes in 2025, including Small Tortoiseshell. While still generally low, abundance of Small Tortoiseshell has increased across the UK, an improvement from 2024 which was its worst recorded year across all four countries.
- 51 species of 58 monitored (88%) showed an increase in abundance at a UK level, a direct reversal of the 2024 result in which 51 species showed a decrease. 7 species (12% showed a decrease in abundance across the UK).
- There were regional differences in how some species fared in 2025:
- In England, 48 species (87%) showed an annual increase compared to 2024, with 1 species (Orange-tip) showing no change in abundance. As with the UK, no species had their best or worst year on record for England.
- 28 of 32 monitored species increased in abundance in Wales when compared to 2024, which was the worst year on record for the country. Only 3 species (9%) showed decreases, while Brown Argus was the only species to show no change from 2024. Small Skipper showed its worst year on record for Wales. No other species returned worst year records in 2025 in Wales.
- Only Orange-tip declined in abundance in Northern Ireland when compared to 2024 data, while the 13 other species monitored showed an increase. 2025 was the 7th best year on record for Northern Ireland. Small Tortoiseshell in particular did very well, increasing in abundance by 900% compared to 2024.
- In Scotland, 21 species of 27 monitored (78%) showed an increase in abundance from 2024 to 2025, while 6 species (22%) showed a decrease in abundance. 5 species in Scotland had their best year on record in 2025, Large White, Small White, Red Admiral, Comma, and Speckled Wood. Pearl-bordered Fritillary increased by 95%, having its second best year since 2002, when sufficient recording began for this species in Scotland. Of those that decreased, Northern Brown Argus fared worst, down by 27%.
Short-term trends
- Short-term trends describe population abundance changes over a period of 10 years, or since recording began if a species has less than a decade of data.
- Some species are doing particularly well in the short-term trends. Heath Fritillary is one such example, which is showing a significant increase over the last 10 years, despite the long-term trend showing decline. This may be attributed to recent local conservation action to boost local Heath Fritillary populations across the UK.
- Across the UK, 33 of the 58 species monitored (57%) are decreasing in abundance, while 25 species (43%) are increasing in abundance.
- England shows similar short-term results to the UK, with 32 species of 55 monitored (58%) decreasing and 23 species (42%) increasing. England is seeing a very significant increase for Lulworth Skipper in the short-term trend, which is notably different from the decline shown in the long-term trend.
- Wales also has similar percentages, with 18 species of 32 monitored (56%) decreasing in abundance, and 13 species (40%) increasing. Small Copper is the only species in Wales to show no change in the short-term trend, despite a decrease in the UK short-term trend. Small Skipper is showing a very significant decrease in the short-term trend, showing a worrying pattern as the long-term trend also shows decreases and 2025 was the worst year on record for the species.
- Data for Northern Ireland shows 9 species of 14 monitored (64%) increasing in abundance, while 5 species (36%) are decreasing. Of note; UKBMS monitoring started later in Northern Ireland, and there is less long-term data.
- Scotland has similar percentages to Northern Ireland, with 18 species of 27 monitored (66%) increasing in abundance over the short-term, and 9 species (34%) decreasing. Speckled Wood is showing significant increases in the short-term trend, mirroring its significant increases in the long-term trend, and its very successful 2025.
Long-term trends
- Long-term trends describe population abundance changes since recording began for each species for which the UKBMS collects data.
- Across the UK, 20 species of 58 monitored (34.5%) show decreasing population abundance over time, while 18 species (31%) show increased population abundance. Twenty species (34.5%) show no long-term change in abundance.
- In England, 32 species of 55 monitored (58%) are decreasing in population abundance over time, while 22 species (38%) are increasing in population abundance. 1 species (2%) is not showing long-term changes in abundance in England.
- 8 species of the 27 monitored in Scotland are decreasing in population abundance over time, while 19 species (70%%) are increasing.
- In Wales, 13 species of the 32 monitored (41%) are increasing in population abundance, while 19 (59%) are decreasing.
- Northern Ireland results show 8 species of 14 monitored (57%) declining in abundance, while 6 (43%) are increasing. Northern Ireland has a much shorter series than the rest of the UK, however clear differences are emerging, such as the Small Tortoiseshell, which continues to do well in Northern Ireland whilst declining elsewhere in the UK.
Table 1: Summary of species trends over the whole period or ten years, for each region.
|
Country |
Total number of species |
Long-term trend |
Long-term trend |
Short-term trend |
Short-term trend |
|
UK |
58 |
20 |
18 |
5 |
3 |
|
England |
55 |
22 |
16 |
5 |
4 |
|
Scotland |
27 |
3 |
12 |
1 |
1 |
|
Wales |
32 |
13 |
9 |
4 |
0 |
|
Northern Ireland |
14 |
3 |
0 |
1 |
0 |
Interpretation of results
Of 59 butterfly species currently known in the UK, the UKBMS consistently provides enough data to monitor long-term population abundance of 58 species. Population abundance trends are not monitored for Mountain Ringlet.
The data do differ regionally, both due to regional differences in population assemblages, and monitoring start dates across the UK. Of note, Northern Ireland has a shorter series than the rest of the UK, and indicates trends quite different from those in the rest of the country. In 2025, both Scotland and Northern Ireland had a ‘better’ year than England and Wales, with Scotland reporting 5 species with their best year of their series in Scotland, and Northern Ireland having their 7th best year since monitoring in the country began. This is reflected in trends for some species: Small Tortoiseshell has been declining in abundance in both long-term and short-term trends across the UK, with the exception of Northern Ireland, where abundance is increasing across all trends and a 900% increase was seen between 2024 and 2025.
Population abundance trends are measured in the short-term and long-term for UKBMS data. Short-term change measures the 10-year trend, while long-term change measures the entire series (since monitoring began, with a maximum of 50 years). Annual change is noted as the change between the current data release and data from the previous year. Annual changes are particularly volatile, and can be extremely weather dependent. 2025, following on from the drastic downturn of 2024, is considered an ‘average’ year, despite the generally good weather and record levels of sunshine across the UK. This is not unexpected: both 2023 and 2024 had record-breaking levels of rainfall, with greatly diminished levels of sunshine. Butterfly populations across the UK fell sharply in response, and the ideal conditions of little rain and lots of sunshine in 2025 led to a recovery from the previous years, rather than the bumper year which may otherwise be expected. Significant years like 2024 can have ripple effects on the short-term trends, which are, to a lesser degree, susceptible to the kind of variability seen in annual trends. Long-term trends give a longer view into how populations are behaving over time, smoothing weather-based fluctuations seen in short-term and annual trends. Long-term trends can provide insight into population responses to ongoing pressures, such as climate change and agricultural intensification. The direction of short- and long-term trends in butterfly abundance is highly dependent on species, as indicated by 57% of species decreasing in abundance across the UK, whilst 43% of species increased. Reasons for these differences could include different species’ responses to land management changes, weather patterns, and pollution, as well as targeted conservation actions for specific species. Short-term and annual trends must be looked at in the context of the full series if trying to understand the impacts of pressures like land-use change and climate change.
Some short-term results can be encouraging, showing the direct impacts of local conservation action and habitat restoration work. Health Fritillary increased in abundance by 236% across the UK from 2024, and is showing a significant increase in abundance in the short-term trend. While the long-term trend still shows some decline, this recent data shows an uptick that can be directly attributed to Butterfly Conservation’s work to create suitable habitat for the species.
Confidence in results
The analytical methods follow standardised, peer reviewed procedures, verified by the Office for Statistics Regulation. The data meet the standards for trustworthiness, value, and quality, as set out in the Code of Practice for Statistics.
UKBMS volunteers are trained to follow standardised, peer reviewed methods for data collection and submission, and the submitted data undergo validation processes run by Butterfly Conservation and the BTO.
Trends are published as Official Statistics when they are considered statistically robust, and where the long-term trends can be used to assess changes in population abundance with confidence. Potential bias is recognised in coverage rates for regions across the UK, particularly in remote regions, and hard to reach sites. Any trends not considered scientifically robust would not be included in the Official Statistic. There are species-specific monitoring methods, such as Purple Hairstreak evening transects, which are accounted for in the statistic.
Drivers of change
Weather conditions can create noticeable fluctuations in butterfly populations from one year to the next as they impact butterfly development and activity directly. Butterflies are ectothermic, and require sunshine in order to function and be active. Sunshine hours will impact butterfly activity levels, timing of the flight period, and how many generations are produced in a year. Low sunshine hours and adverse weather (i.e. rain and cloudiness) can have deleterious impacts on butterfly populations that can take years to recover from. According to Met Office Data, 2025 was the UK’s warmest and sunniest year on record. Sunshine hours exceeded the previous record (2003) by over 60 hours. This marks a strong contrast to 2023 and 2024, which recorded below average levels of sunshine, with May 2024 achieving record levels of rainfall. The spring and summer in 2025 were particularly warm and dry, the prolonged sunny weather proving beneficial for butterfly species across the UK. Only two months recorded below average sunshine, while the spring was the fourth sunniest on record and the sunniest since 1995. Northern Ireland recorded over 300 hours of sunshine in May 2025; the highest monthly sunshine ever recorded in Northern Ireland. Winter temperatures can also impact butterfly populations, wet and mild winters can result in flooding and an increase in pathogens and predation on eggs and overwintering caterpillars. The winter of 2024/25 saw a number of storms hit the UK but overall lower than average rainfall. Northern Ireland, in particular, saw only 70% of average winter rainfall across the winter. The winter was warmer than average, but not warm enough to see overwintering butterflies emerge until temperatures rose in April.
Drivers of long-term declines in abundance include changes in the extent, condition, and fragmentation of habitats caused by a combination of local intensification of farming, forestry, and urban development. In particular, many natural and semi-natural habitats have been declining in both range and quality, both as a result of change in land-use and increasing agricultural intensification and use of herbicides and fertilisers. Herbicide use in the agricultural industry has a direct impact on butterfly abundance in the UK. Changing land management techniques, specifically of heathland and grassland habitats, can lead to population abundance decline as quality declines or the habitat changes. In areas where grazing and controlled burning has stopped being used, successional processes can lead to the habitat becoming completely unsuitable for specific species. Graylings, for example, need areas of bare ground: if scrub starts to grow then the Grayling will not survive. In Worcestershire, programmes of grazing and scrub management have been successfully used to help increase localised Grayling populations.
Climate change has longer term implications for butterfly populations, but will likely see mixed, species-dependent reactions with some species declining and others increasing in abundance. Spring-flying species have been emerging progressively earlier as temperatures become increasingly warm. The data reflect that some species which traditionally produced one brood annually are able to produce second broods as springs become warmer and summers grow longer. For example, Wood White now regularly produces second broods on monitored sites. Not all taxa respond similarly, meaning that butterflies are at risk of emerging before their food sources are ready and populations could decrease as individuals struggle. Species ranges are also changing with long-term climatic changes. Species traditionally found in southern regions of the UK are increasingly being found in northern regions as temperatures increase. Migratory species have also been found overwintering in the UK, rather than migrating further south. Habitat specialists could be at higher risk, as they may struggle to colonise declining and increasingly fragmented habitats.
Targeted habitat conservation and land management activity can have positive impacts on species abundance. Some increases noted in UKBMS data can be traced directly to conservation action and proper habitat management, for example Heath Fritillary is a threatened habitat specialist that has benefited from protection and restoration work. Similarly, managed grazing regimes have successfully been used to help Silver-spotted Skipper and Grayling populations across the UK, while the Large Blue has been successfully reintroduced to grasslands in Gloucestershire and Somerset.
Background and methods
Data collection
The UKBMS dataset is comprised of the results of three surveys; traditional UKBMS transects, UKBMS targeted surveys, and the Wider Countryside Butterfly Survey (WCBS). Traditional transects make up the bulk of the data, and involve a volunteer walking a fixed route, split into sections, every week with suitable weather from April to September recording every butterfly seen on the walk. Targeted surveys use different methods depending on the habitat or species being targeted. These survey methods include both transect walks and alternatives such as timed counts. WCBS is a ‘reduced effort’ option, which requires at least 2 visits to a randomly allocated square in a volunteer’s local area. Volunteers are trained to record their findings, as well as habitat and weather data, and upload their data to the UKBMS online recording portal.
Data repositories
The online data repository for the UKBMS is the BRC Indicia warehouse. The online recording portal and the Indicia Warehouse have systems to help validate data, including the ability for experts to check and review data. The other data repository for UKBMS data is the UKBMS database. The UKBMS database hosts all UKBMS legacy data, alongside Indicia Warehouse data that has undergone verification and validation.
Validation and verification
A number of checks occur for data uploaded to the online repository. Area checks for each species occurrence point against the most recent Butterfly Atlas highlight any observations falling outside of the expected species range. Area checks may also flag dubious observations of new species at a site, but if not caught, existing sites recording a new species are checked automatically. Similarly, data is checked against expected flight periods for each species to highlight any falling out of their expected periods. Some species are expected to fly for the whole season, so flight period checks may not be applicable. Rare species may require more in-depth checks, due to the outsize impact of single observations on species data. Counts for rare species that are exceptionally high or low, or that are out of the norm for expected range, flight period, or weather will be automatically checked. Any flags raised will be checked by experts for potential misidentification or recording errors. Checked observations may be kept, queried with the recorder, modified, or removed.
Any transects walked outside of the criteria conditions for weather and time of day will be removed.
Analyses
Annual collated indices of species abundance are produced using the Generalized Abundance Index (GAI). It first estimates yearly seasonal abundance curves for each species using Generalised Additive Models fitted to data from all relevant sites, normalizes these curves, and uses them to adjust for gaps in survey coverage so that each site receives a corrected annual total. These corrected site indices are then modelled using Generalised Linear Models with site and year as predictors, weighted by how well each site was sampled, and the resulting year coefficients form the collated national or regional indices. Trends are then derived by fitting simple linear models to these collated indices, allowing estimation of annual and overall percentage changes in abundance across the time series.
Involvement and contacts
This analysis was produced by the UK Centre for Ecology with quality assurance from Butterfly Conservation, the British Trust for Ornithology, and JNCC.
These data are published as part of JNCC's Official Statistics. If you have queries or comments, please contact feedback@jncc.gov.uk.
Relation to other Official Statistics
The Official Statistic 'Abundance of UK Butterflies’ feeds into the National Statistics Compendium UK Biodiversity Indicators.
These statistics forms part of a suite of statistics produced through partnership monitoring schemes as part of JNCC’s broader evidence provision.
UKBMS data are used in scientific research and to inform conservation action.
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