35 years of butterfly monitoring in Flanders
In 1991, Flanders, together with the Netherlands, began standardised monitoring of butterflies. Currently, we monitor butterflies in Flanders at just around 20 fixed transects. In 2016, however, the monitoring network for Flemish priority butterflies was added. This enables us to identify trends for 21 common butterflies. Since the start of the counts, no fewer than 434,480 butterflies have been recorded, comprising 56 different species.
In the period 1991–2025, we see:
- five clear losers: the large skipper, the small tortoiseshell, the ringlet, the Hedge brown and the Essex skipper
- three clear winners: the red admiral, the speckled wood and the common brimstone
- seven species that remain more or less stable, such as the European peacock and the orange tip
- six species with significant fluctuations, for example the holly blue and the common copper
Grassland butterflies are declining by an average of 58%. This is likely due to the decline of nutrient-poor, flower-rich grasslands caused by habitat loss and nitrogen deposition. Forest-related species increased sharply between 2000 and 2017, but have remained more or less stable since then.
The trends in Flanders are entirely in line with those in other European countries. To enable us to adjust our nature conservation policy even more quickly and reliably, an expansion of the number of monitoring routes is desirable.
Picture above: The hedge brown is in significant decline along the butterfly routes in Flanders (photo: Dirk Maes)