Grassland butterflies declined dramatically between 1990 and 2011, a new report from the European Environment Agency has shown. The EEA said the decline has been caused by intensifying agriculture and a failure to properly manage grassland ecosystems.

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The fall in grassland butterfly numbers is particularly worrying, according to the report, because these butterflies are considered to be representative indicators of trends observed for most other terrestrial insects, which together form around two thirds of the world's species. This means that butterflies are useful indicators of biodiversity and the general health of ecosystems.

The EEA report looked at seventeen butterfly species in 19 European counties, of which 10 species were widespread and seven were 'specialist' species, reliant on a certain type of habitat. Of the 17 species, eight were shown to have declined in Europe, two remained stable and one increased. For six species the trend is uncertain.

Hans Bruyninckx, EEA Executive Director, said on Tuesday (23rd July), "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. We must recognise the importance of butterflies and other insects – the pollination they carry out is essential for both natural ecosystems and agriculture."

Why are butterflies disappearing?

As well as intensifying agriculture, the report's authors said "abandoned land" is also affecting butterflies. Whereas agriculture has intensified where the land is relatively flat and easy to cultivate, large areas of grasslands have been abandoned by farmers in upland and wet regions, mainly in eastern and southern Europe. Both intensification and 'rewilding' of land have led to a reduction in suitable habitat for grassland butterflies.

Agricultural intensification creates uniform grasslands which are almost sterile for biodiversity. In addition, butterflies are also vulnerable to pesticides, often used in intensively managed farming systems, EEA said. On the other hand, the abandonment of uplands farms, usually for socio-economic reasons (i.e. where farming on low-productivity land brings only a small amount of income and CAP funding is minimal) means unmanaged land quickly reverts to scrub and woodland. Although this process is shrinking grassland butterflies' range, it carries other biodiversity benefits.

Even so, EEA said that, in some regions of north-western Europe, grassland butterflies are now almost restricted to road verges, railway sidings, rocky or wet places, urban areas and nature reserves. The authors added that areas using traditional low-input farming systems, known as High Nature Value Farmland, are also important habitats.

EEA said that, as current changes in land use began before 1990, its findings suggest that the recent halving of butterfly numbers may only be the most recent development in a much larger long-term decline. The Agency also claims its European Grassland Butterfly Indicator could be used as a measure of success of agriculture policies, helping EU leaders achieve the goal of halting the loss of biodiversity by 2020.