Butterflies normally found on grassland are in steep decline across Europe, pointing to a huge loss of European biodiversity.
This is the conclusion of a new study by Butterfly Conservation Europe based on data from 3,000 sites in 15 countries.
The Grassland Butterfly Indicator shows that the populations of 17 butterfly species have declined by over 70% in the last 20 years.
Butterflies are sensitive environmental indicators; alerting us to underlying problems with the environment. Grasslands are a vital habitat for European wildlife and support a huge range of plants and insects. If butterfly numbers are falling, inevitably other wildlife is also in decline.
The losses are thought to have been caused by rapidly changing agricultural practices in Europe's diverse semi-natural grasslands.
Such grasslands have been created by traditional livestock grazing and hay-making over centuries of human occupation since the last ice-age.
This management creates a wonderfully flower-rich breeding habitat for butterflies and many other insects. However, in recent decades these traditional grasslands have deteriorated, meaning loss due to agricultural intensification in some regions and abandonment in others.
The underlying forces behind the losses are rapid economic and social changes, which have led to the intensification of better land and the abandonment of land with poorer soils and in remote locations.
Abandonment is thought to be the most serious cause of losses in mountain regions and eastern Europe, while lowland areas have suffered most from intensification.
Dr Martin Warren, Chief Executive at Butterfly Conservation (UK), said: "The results show the dramatic and continuing loss of biodiversity in European grasslands.
"We urgently need a change in EU agricultural policy that favours High Nature Value farming rather than over-intensification as at present. The results would be better for the environment and better from rural communities who are struggling to survive under the current system of support which favours larger more intensive producers."
Butterflies are one of the best monitored groups of wildlife in Europe and Butterfly Conservation Europe is pressing for them to be adopted as agricultural indicators in the next round of Common Agricultural Policy reform in 2013.