LIST co-authored report shows number of European grassland butterflies on the decline

If the flapping of their tiny proverbial wings in one corner of the world can predict a tornado in another (cf. the so-called “butterfly effect”), butterflies are also excellent indicators of how well or how poorly our environment is doing. And if recent findings are to go by, the picture looks pretty grim. The number of grassland butterflies in Europe is dwindling, says the recently updated European Grassland Butterfly Indicator, a crucial measure in assessing the health of European grasslands. The report was co-authored by LIST researchers and compiled by the association Butterfly Conservation Europe.

“We have been working with the Luxembourg Ministry of the Environment, Climate and Sustainable Development since 2010 within the scope of our biodiversity monitoring programmes,” says Xavier Mestdagh, co-author, “And we have been using a standardized method called the Pollard Walk to conduct butterfly surveys.”

Named in honour of Ernie Pollard, who designed the methodology in the 1970s, these transect walks are used all over the world to record the number of butterflies. In Europe, butterflies are counted by citizens and professionals in different countries or regions, and these counts are then centralized by Butterfly Conservation Europe. These standardized records, mostly often citizen-based, feed into statistical analyses to produce indicators of nature's health and biodiversity.

“Butterflies are very useful bioindicators due to their quick reproductive cycles, typically having one or two generations per year,” added Sarah Vray, another co-author. Consequently, any environmental change can be detected more rapidly compared to species such as birds or mammals, which have longer lifespans and breeding cycles. Additionally, butterflies are relatively easy to observe and can be found in various habitats, often displaying specificity to particular plants or environmental conditions such as temperature and moisture.

In Luxembourg, LIST coordinates the butterfly monitoring programmes, but the association natur&ëmwelt a.s.b.l. and an increasing number of volunteer citizens have been participating in transect walks to collect data with the aim of producing a standardized index of abundance of butterflies over time, contributing ultimately to the report.

The results at the European scale suggest that the indicator has experienced a significant fall over the past decades. There has been a decline in butterfly abundance of 36% since 1990 across Europe in the last ten years, and by 32% across the EU Member States. Conservationists are attributing it to the intensification of farming, land abandonment and intensity of heatwaves and droughts, largely due to climate change.

There is hope though, as the indicator is going to be adopted within the EU's forthcoming Nature Restoration Law, which aims to combat the declining populations of wild insect pollinators and restore balance to ecosystems. The proposed legislation includes enforceable objectives aimed at reversing the trend.

The report, which can be read here, was co-authored by Xavier Mestdagh, Sarah Vray and Nicolas Titeux from the department of Environmental Research and Innovation at LIST.