A new report on trends of grassland butterflies across Europe shows numbers declined by over a third in just a decade.

The European Grassland Butterfly Indicator, led by the Butterfly Conservation Europe and the UK Centre for Ecology & Hydrology (UKCEH), is based on an aggregate of abundance trends of 17 common species. It shows that numbers of butterflies in this habitat declined by 36 per cent in the last decade after being relatively stable for the previous 20 years.

The research team of almost 70 scientists from institutes across Europe say the main factor behind the declines is agricultural intensification. This has involved either the conversion of grasslands to arable fields or the heavy use of fertilisers and herbicides which reduce the wildflowers on which butterflies breed. Nitrogen pollution from agriculture and car exhausts is also a growing factor as is climate change, which has a negative impact on some species.

The trends within the report are based on 5.5 million records submitted by volunteers between 1990 and 2020.

Dr David Roy, Head of the Biological Records Centre at UKCEH, senior author of the report, said: “This indicator uses the rapidly expanding network of butterfly monitoring schemes across Europe – the most comprehensive large-scale insect dataset anywhere in the world. This fantastic citizen science initiative relies on thousands of skilled volunteers. 

“This dataset is vital to understand the status of butterflies as important pollinators, and to indicate the quality of habitats. Trends of species will therefore be useful indicators of the progress of EU and UK targets to reverse biodiversity loss by 2030.”

The Large Blue is one of the biggest losers across Europe where it has declined by 82 per cent in the last 30 years. However, it was re-introduced successfully into the UK by UKCEH and Natural England in the 1970s after becoming extinct here, showing conservation measures can be successful. The Wall has declined by 68 per cent across Europe and has also declined steeply in the UK, with nitrogen deposition being thought to be a major factor. Adonis Blue and Small Heath have also declined over 60 per cent.

The European results echo the findings of the recent State of the UK’s Butterflies report, produced by Butterfly Conservation, UKCEH and the British Trust for Ornithology. This showed 80 per cent of UK butterflies have decreased in either abundance or distribution, and many species are at risk of extinction. 

The species declines have important implications for wildlife and food production. Butterflies are good barometers of the fortunes of other insects and the general health of habitats, for they are sensitive to environmental changes and play an essential role in ecosystems. Insects are important food sources for other animals such as birds and bats, as well as being pollinators of most wildflowers as well as certain crops.

The European Grassland Butterfly Indicator 1990-2020 Technical report is available on the Dutch Butterfly Conservation website.