European common blue butterfly (Polyommatus icarus) in the Doñana National Park // Credit: J. Manuel Vidal Cordero

Butterfly populations are characterised by year-to-year fluctuations, however long-term trends reveal their actual status. Between 1991 and 2020, the numbers of 15 typical grassland butterfly species declined strongly by 29.5%, according to data from 18 EU Member States. Although this indicator uses 1991 as a baseline, substantial decreases in species abundance, richness and diversity had occurred before this date. Data from the European Butterfly Monitoring Scheme (eBMs) has been used for this index. The ICTS-Doñana of the Doñana Biological Station – CSIC actively participates in this program by providing periodical monitoring data of butterflies in the Doñana National Park.

The main drivers of the decline in grassland butterfly numbers are agricultural intensification and changes in land use, such as habitat loss, fragmentation and degradation. Agricultural intensification entails high inputs of agrochemicals, including pesticides, which can dramatically reduce insect populations, including butterflies. 

According to the European Environment Agency publishes this index, it is difficult to forecast how soon butterfly populations can recover, as they are influenced by a combination of socio-economic and environmental factors and policy measures. Although some measures set out in the Habitat Directive have helped some populations, the declines continue to occur both inside and outside of protected areas.

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Index included in the new Nature Restoration Law

Butterflies react rapidly to changes in their habitats, hence they are a valuable indicator of the health of the environment and can help measure progress towards EU biodiversity targets. In addition, they play an important role in the functioning of ecosystems and provide a range of services. They pollinate crops and wild plants and serve as a food source for other animals throughout all stages of their life cycle.

This grassland butterfly index is included among three indicators in agricultural ecosystems included in the EU regulation on nature restoration, recently adopted. The member states have to select at least two of the three indicators, including indicators on the share of agricultural land with high-diversity landscape features and the stock of organic carbon in cropland mineral soil, to put measures aiming to achieve increasing trends before 2030. 

Reference

Grassland butterfly index - EU aggregate, Butterfly Conservation Europe, European Butterfly Monitoring Scheme partnership, SPRING project. Data Set: https://ec.europa.eu/eurostat/databrowser/view/sdg_15_61/default/table?lang=en