C6. Insects of the wider countryside (butterflies)
a. Habitat specialists
b. Species of the wider countryside
Type: State Indicator
Introduction
This indicator consists of two measures of annual butterfly population abundance: the first for habitat specialist butterflies (species strongly associated with semi-natural habitats such as chalk downland) and the second for more widespread butterflies found in both semi-natural habitats and the wider countryside.
Butterflies are complementary to birds and bats as an indicator, especially the habitat specialists, because they use resources in the landscape at a much finer spatial scale than either birds or bats.
Contents
- Key results
- Habitat Specialists
- Species of the wider countryside
- Assessment of change in butterfly populations
- Relevance
-
Background
- Figure C6iia. Trends for the abundance of butterflies of the wider countryside on UK farmland, 1990 to 2021.
- Figure C6iib. Long-term and short-term changes in individual species’ trends for butterflies of the wider countryside on UK farmland, 1990 to 2021.
- Figure C6iiia. Trends for butterflies of the wider countryside in UK woodland, 1990 to 2021.
- Figure C6iiib. Long-term and short-term changes in individual species’ trends for butterflies of the wider countryside in UK woodland, 1990 to 2021.
- Figure C6iva: Trends for the abundance of all species of butterflies resident in the UK, 1976 to 2021.
- Figure C6ivb. Long-term and short-term changes in individual species’ trends for all species of butterflies resident in the UK, 1976 to 2021.
- Goals and Targets
- Web links for further information
- Downloads
Key results
Overall, 2021 was a slightly below average year for butterflies in the UK, with 67% (34 from 51) of all species contributing to the UK indicators falling in abundance from the previous year. An unusually cold spring was followed by high rainfall in the south-east, while central areas recorded the lowest August sunshine figures for 60 years.
Since 1976, the unsmoothed habitat specialist butterfly index has fallen by 60% (Figure C6ia). Over the same period, the unsmoothed index for species of the wider countryside has fallen by 37% (Figure C6ib).
Large fluctuations in numbers between years are a typical feature of butterfly populations, principally in response to weather conditions, hence the statistical assessment of change is made on an analysis of the underlying smoothed rather than unsmoothed trends. Over the long term (since 1976), populations of habitat specialist butterflies have declined significantly though species of the wider countryside show no significant change. Since 2016, both short-term trends show no significant change.
Habitat Specialists
Figure C6iai. Trends in abundance of habitat specialist butterflies in the UK, 1976 to 2021.
Figure C6iaii. Long-term and short-term changes in individual species’ trends for habitat specialist butterflies in the UK, 1976 to 2021.
Notes:
- This indicator includes individual measures for 26 species of butterflies.
- Figure C6iai (the line graph) shows the unsmoothed trend (dashed line) and the smoothed trend (solid line) together with its 95% confidence interval (shaded area).
- Figure C6iaii (the bar chart) shows the percentage of species within the indicator that have shown a statistically significant increase, a statistically significant decrease or no statistically significant change (little change).
- Recent improvements to the methodology mean the charts presented here are not directly comparable to those presented in releases prior to 2020.
Source: Butterfly Conservation; UK Centre for Ecology & Hydrology; Defra; British Trust for Ornithology; Joint Nature Conservation Committee.
Habitat specialist butterflies, which are vulnerable to semi-natural habitat loss and fragmentation, have not recovered from declines experienced in the late 1970s. These declines were mainly attributed to the knock-on effects of the drought conditions experienced in 1976. Overall, the unsmoothed habitat specialist index declined by 60% between 1976 and 2021 (Figure C6iai). Analysis of the smoothed trend shows a statistically significant reduction in relative abundance over the long-term period driven by decreases in 1976 to 1979. The unsmoothed index showed a 48% increase over the period 2016 to 2021, however, analysis of the smoothed trend showed no statistically significant short-term change.
Individual butterfly species fare differently within the overall trend. Habitat specialists showing the greatest long-term decline since 1976 include heath fritillary; wood white; Lulworth skipper; grayling; and small pearl-bordered fritillary. No species show a significant short-term decline since 2016. Habitat specialists showing the largest long-term increases include silver-spotted skipper; black hairstreak; large heath; dark-green fritillary; and silver-washed fritillary, and of these, dark-green fritillary also showed a statistically significant increase since 2016. Chalk-hill blue increased significantly over the short term but showed no significant long-term change and both grayling and grizzled skipper increased significantly over the short term whilst showing significant long-term declines.
Species of the wider countryside
Figure C6ibi. Trends for the abundance of butterflies of the wider countryside in the UK, 1976 to 2021.
Figure C6ibii. Long-term and short-term changes in individual species’ trends for butterflies of the wider countryside in the UK, 1976 to 2021.
Notes:
- This indicator includes individual measures for 25 species of butterflies; the wider countryside index, however, only includes 24 trends. This is because an aggregate trend is used for small skipper (Thymelicus lineola) and Essex skipper (Thymelicus sylvestris) and has been retained for indicator consistency; these two species were combined due to historical difficulties with distinguishing between them in the field.
- Figure C6ibi (the line graph) shows the unsmoothed trend (dashed line) and the smoothed trend (solid line) together with its 95% confidence interval (shaded area).
- Figure C6ibii (the bar chart) shows the percentage of species trends within the indicator that have shown a statistically significant increase, a statistically significant decrease or no statistically significant change (little change).
- Recent improvements to the methodology mean the charts presented here are not directly comparable to those presented in releases prior to 2020.
Source: Butterfly Conservation; UK Centre for Ecology & Hydrology; British Trust for Ornithology; Defra; Joint Nature Conservation Committee.
The unsmoothed butterflies of the wider countryside index showed a decrease of 37% between 1976 and 2021 (Figure C6ibi); however, analysis of the smoothed trend shows the change was not statistically significant. The unsmoothed index showed a 20% increase over the period 2016 to 2021, however, analysis of the smoothed trend also showed this short-term change is not statistically significant either.
Individual butterfly species again fare differently within the overall trend. Species of the wider countryside showing the greatest declines since 1976 include wall; small tortoiseshell; white-letter hairstreak; small heath; and gatekeeper. No wider countryside butterfly species show a significant short-term decline since 2016. Ringlet; comma; speckled wood; and marbled white show the largest significant increases over the long term, but no species of wider countryside butterflies show a significant increase over the short term.
Assessment of change in butterfly populations
| Long term | Short term | Latest year | |
| Habitat specialists |
|
|
No change (2021) |
| Species of the wider countryside |
|
|
Decreased (2021) |
Note: While percentage changes and latest year changes in these indices are reported based on the most recent unsmoothed data point (2021), the formal long-term and short-term assessments of the statistical significance of these changes are made using the smoothed data to 2021. Analysis of the underlying trends is performed by the data providers.
Relevance
Butterflies are considered to provide a good indication of the broad state of the environment because they respond rapidly to changes in environmental conditions and habitat management, occur in a wide range of habitats, and are representative of many other insects, in that they utilise areas with abundant plant food resources. Butterflies are complementary to birds and bats as indicator species, especially the habitat specialists, because they use resources in the landscape at a much finer spatial scale than either birds or bats.
Background
This indicator is comprised of two multi-species indices compiled by Butterfly Conservation (BC) and the UK Centre for Ecology & Hydrology (UKCEH) from data collated through the UK Butterfly Monitoring Scheme (UKBMS) including from the Wider Countryside Butterfly Survey (WCBS). The indicator includes individual measures for 26 habitat specialist butterflies (low mobility species restricted to semi-natural habitats) and 25 more widespread butterflies (which use both semi-natural and general countryside habitats). It uses butterfly count data collected at 6,221 sample locations across the UK – 3,996 UKBMS butterfly transect and reduced effort sites and 2,225 randomly selected 1 km squares of the WCBS (see the UKBMS sites details map for further information).
Since 2019, 2 additional multi-species indices have also been compiled for butterflies in the UK: the first for butterflies of the wider countryside on farmland, the second for butterflies of the wider countryside in woodland. Although these habitat-specific measures are not included within the formal assessment for the ‘Insects of the wider countryside’ indicator, they are presented here in order to give a more complete picture of the trends for UK butterfly populations.
The 2 habitat indices include 23 species of wider countryside butterflies surveyed on farmland and 25 species surveyed in woodland using data collected at 4,157 locations with farmland habitat and 2,905 locations with woodland habitat (these farmland and woodland locations are subsets of the 6,221 locations shown in UKBMS sites details map. While these habitat specific measures are compiled from a subset of the species in the UK wider countryside butterflies indicator, the base year for the long-term trends is 1990 rather than 1976. This is because prior to this date, there are insufficient data for a number of species included within the 2 indices.
An annual ‘all-species’ index is also compiled for butterflies that are resident in the UK. As with the additional wider countryside indices, this measure in not formally assessed but it is included here in order to give a higher-level picture of the trend for UK butterfly populations. The ‘all-species’ index includes 51 species of butterflies (26 habitat specialists and 25 species of the wider countryside) and uses data collected at the same 6,221 locations as the 2 core measures (see UKBMS sites details map). It does not include regular migrant species or rarer species with less complete data runs.
While the UK wider countryside butterfly measure, the additional wider countryside farmland and woodland measures and the UK ‘all-species’ measure include 25, 23, 25 and 25 species of wider countryside butterflies respectively, they all include one less trend each. This is because an aggregate trend is used for small skipper (Thymelicus lineola) and Essex skipper (Thymelicus sylvestris). These 2 species have been combined due to historical difficulties with distinguishing between them in the field.
The year-to-year fluctuations in butterfly numbers are often linked to natural environmental variation, especially weather conditions. Therefore, in order to identify underlying patterns in population trends, the assessment of change is based on smoothed indices. The smoothed trend in the multi-species indicator is assessed by structural time-series analysis. A statistical test is performed using the software ‘TrendSpotter’ to compare the difference in the smoothed index in the latest year versus other years in the series. Within the measures, each individual species trend is given equal weight, and the annual figure is the geometric mean of the component species indices for that year.
Populations of individual species within each measure may be increasing or decreasing, irrespective of the overall trends. The bar charts provided alongside each trend graph (Figures C6iaii, C6ibii, C6iib, C6iiib and C6ivb) show the percentage of species within that indicator that have shown a statistically significant increase, a statistically significant decrease or no statistically significant change (little change). A list of species included within each index, together with a summary of the estimated long-term and short-term changes for each species and an assessment of the individual species trends can be found in the accompanying dataset.
As there are delays in data submission, data for previous years are also updated retrospectively. This means that the species indices for individual years may vary from previous publications.
Further details of the methods used can be found on the UKBMS website and in the technical background document for this indicator.
Butterflies of the wider countryside on farmland
The unsmoothed butterflies of the wider countryside on farmland index for the UK decreased by 11% between 1990 and 2021 but increased by 24% in the five years to 2021 (Figure C6iia,b). Analysis of the smoothed trends shows that neither the long-term (1990 to 2021) nor short-term (2016 to 2021) changes are statistically significant.
Figure C6iia. Trends for the abundance of butterflies of the wider countryside on UK farmland, 1990 to 2021.
Figure C6iib. Long-term and short-term changes in individual species’ trends for butterflies of the wider countryside on UK farmland, 1990 to 2021.
Notes:
- This indicator includes individual measures for 23 species of butterflies; the UK farmland index, however, only includes 22 trends. This is because an aggregate trend is used for small skipper (Thymelicus lineola) and Essex skipper (Thymelicus sylvestris) and has been retained for indicator consistency; these two species were combined due to historical difficulties with distinguishing between them in the field.
- Figure C6iia (the line graph) shows the unsmoothed trend (dashed line) and the smoothed trend (solid line) together with its 95% confidence interval (shaded area).
- Figure C6iib (the bar chart) shows the percentage of species trends within the indicator that have shown a statistically significant increase, a statistically significant decrease or no statistically significant change (little change).
- Recent improvements to the methodology mean the charts presented here are not directly comparable to those presented in releases prior to 2020.
Source: Butterfly Conservation; UK Centre for Ecology & Hydrology; British Trust for Ornithology; Defra; Joint Nature Conservation Committee.
Individual butterfly species fare differently within the overall stable trend. Species in significant long-term decline on farmland include small tortoiseshell; wall; Scotch argus; gatekeeper; and large skipper. No species decreased on farmland over the short term (since 2016). Three species, the ringlet; brimstone; and speckled wood, increased significantly on farmland over the long term, but no species have increased significantly over the short term.
Butterflies of the wider countryside in woodland
The unsmoothed butterflies of the wider countryside in woodland index for the UK decreased by 59% between 1990 and 2021 but increased by 11% in the five years to 2021 (Figure C6iiia,b). Analysis of the smoothed trends shows a statistically significant long-term decline since 1990 but no significant change in the short term.
Figure C6iiia. Trends for butterflies of the wider countryside in UK woodland, 1990 to 2021.
Figure C6iiib. Long-term and short-term changes in individual species’ trends for butterflies of the wider countryside in UK woodland, 1990 to 2021.
Notes:
- This indicator includes individual measures for 25 species of butterflies; the UK woodland index, however, only includes 24 trends. This is because an aggregate trend is used for small skipper (Thymelicus lineola) and Essex skipper (Thymelicus sylvestris); these two species have been combined due to historical difficulties with distinguishing between them in the field.
- Figure C6iiia (the line graph) shows the unsmoothed trend (dashed line) and the smoothed trend (solid line) together with its 95% confidence interval (shaded area).
- Figure C6iiib (the bar chart) shows the percentage of species trends within the indicator that have shown a statistically significant increase, a statistically significant decrease or no statistically significant change (little change).
- Recent improvements to the methodology mean the charts presented here are not directly comparable to those presented in releases prior to 2020.
Source: Butterfly Conservation; UK Centre for Ecology & Hydrology; British Trust for Ornithology; Defra; Joint Nature Conservation Committee.
The long-term decline of woodland butterflies is thought to be due to a lack of woodland management and loss of open spaces in woods. Species showing the greatest long-term declines in woodland include wall; small copper; small tortoiseshell; Essex/small skipper; and gatekeeper. No species show a significant decline in the short term. Ringlet displayed the same trends in woodland as on farmland, increasing significantly in both habitats over the long term, but showing no significant change since 2016. No other woodland butterflies show a significant long-term increase and none show a significant increase over the short term.
UK ‘all-species’ index
The unsmoothed ‘all-species’ butterflies index for the UK declined by 43% between 1976 and 2021, but the index increased by 34% in the 5 years to 2021 (Figure C6iva,b). The assessment of change for this measure is once again made on an analysis of the smoothed trend; this trend shows long-term (1976 to 2021) and short-term (2016 to 2021) declines that are both statistically significant.
Individual butterfly species fare differently within the overall declining long-term trend. Species in significant long-term decline across the UK include heath fritillary; wall; wood white; small tortoiseshell; white-letter hairstreak; and Lulworth skipper. No species showed a significant decline over the short term. Species displaying the greatest statistically significant increases over the long term include silver-spotted skipper; black hairstreak; large heath; ringlet; dark green fritillary; and silver-washed fritillary. Dark green fritillary also increased significantly over the short term as did silver-studded blue. Chalk hill blue increased significantly over the short term but showed no long-term change while grayling and grizzled skipper increased significantly over the short term but showed significant long-term declines.
Figure C6iva: Trends for the abundance of all species of butterflies resident in the UK, 1976 to 2021.
Figure C6ivb. Long-term and short-term changes in individual species’ trends for all species of butterflies resident in the UK, 1976 to 2021.
Notes:
- This indicator includes individual measures for 51 species of butterflies; the UK ‘all-species’ butterflies’ index, however, only includes 50 trends. This is because an aggregate trend is used for small skipper (Thymelicus lineola) and Essex skipper (Thymelicus sylvestris); these 2 species have been combined due to historical difficulties with distinguishing between them in the field.
- Figure C6iva (the line graph) shows the unsmoothed trend (dashed line) and the smoothed trend (solid line) together with its 95% confidence interval (a measure of uncertainty) represented by the shaded area on the chart.
- Figure C6ivb (the bar chart)shows the percentage of species within the indicator that have shown a statistically significant increase, a statistically significant decrease or no statistically significant change (little change).
Goals and Targets
Aichi Targets for which this is a primary indicator
Strategic Goal B. Reduce the direct pressures on biodiversity and promote sustainable use.
Target 7: By 2020, areas under agriculture, aquaculture and forestry are managed sustainably, ensuring conservation of biodiversity.
Strategic Goal C. To improve the status of biodiversity by safeguarding ecosystems, species and genetic diversity.
Target 12: By 2020, the extinction of known threatened species has been prevented and their conservation status, particularly of those most in decline, has been improved and sustained.
Aichi Targets for which this is a relevant indicator
Strategic Goal B. Reduce the direct pressures on biodiversity and promote sustainable use.
Target 5: By 2020, the rate of loss of all natural habitats, including forests, is at least halved and where feasible brought close to zero, and degradation and fragmentation is significantly reduced.
Strategic Goal C. To improve the status of biodiversity by safeguarding ecosystems, species and genetic diversity.
Target 11: By 2020, at least 17 per cent of terrestrial and inland water, and 10 per cent of coastal and marine areas, especially areas of particular importance for biodiversity and ecosystem services, are conserved through effectively and equitably managed, ecologically representative and well connected systems of protected areas and other effective area-based conservation measures, and integrated into the wider landscape and seascapes.
Web links for further information
| Reference | Title |
|
Butterfly Conservation |
|
|
UK Butterfly Monitoring Scheme |
Butterflies as indicators |
Downloads
Download the Datasheet and Technical background document from JNCC's Resource Hub.
A more general technical document on UKBMS official statistics is available.
Evidence Statements (2016) for C6a and C6b, along with more information on the project, are available from Defra's website.
Last updated: December 2022
Latest data available: 2021
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