Europe lost nearly half of its grassland butterflies between 1990 and 2011, the European Environment Agency says in a new report.
"This dramatic decline in grassland butterflies should ring alarm bells - in general Europe's grassland habitats are shrinking. If we fail to maintain these habitats we could lose many of these species forever," EEA Executive Director Hans Bruyninckx said.
Eight of the 17 butterfly species that were the focus of the report, "The European Grassland Butterfly Indicator: 1990-2011", showed declines.
The numbers are "particularly worrying", according to the EEA, because butterflies have proven to be "useful indicators of biodiversity and the general health of ecosystems".
The EEA's analysis was based on information from national butterfly monitoring schemes in 19 nations, most of them members of the European Union.
EEA researchers identified "intensifying agriculture" as one of the principal factors affecting the populations of grassland butterflies.
"Agricultural intensification leads to uniform grasslands which are almost sterile for biodiversity. In addition, butterflies are also vulnerable to pesticides, often used in intensively managed farming systems," the report says.
Subsidies and incentive payments to farmers and other rural landowners under the EU's Common Agricultural Policy could be targeted to promote better stewardship of the countryside, the EEA said.