Monitoring of the butterfly population in Flanders 1991-2024: more losers than winners
Butterfly monitoring in Flanders is done on a modest scale. The number of butterfly monitoring routes in Flanders has always remained fairly modest (20-40) and never reached the numbers in the United Kingdom or the Netherlands, where several hundred butterfly monitoring routes are walked every year.
Since 1991, monitoring of butterflies has been carried out in Flanders, where volunteers walk a fixed route every week from the beginning of April to the end of September and count the number of butterflies they encounter along the way.
In the period from 1991-2024, a total of 55 species of butterflies were observed, but only for 21 species was there sufficient data available to conduct a trend analysis.
In the period 1991-2024:
- There are six species that show a declining trend: large skipper, small tortoiseshell, ringlet, map, gatekeeper and Essex skipper.
- Four species are increasing: red admiral, speckled wood, common brimstone and European peacock.
- The other species show a stable (5 species) or uncertain trend (6 species).
Grassland species are declining by an average of 58% compared to the starting year 1991, which may be due to the disappearance and loss of quality of nutrient-poor, flower-rich grasslands due to nitrogen deposition and climate change. Forest-related species initially increased sharply in the period 2001-2017, but have since shown a fairly sharp decline (with greater differences between years than with grassland butterflies). Additional ecological research is needed to identify a cause of this recent decline in ‘forest species’.
Since 2016, twelve Red List butterflies have been monitored in a separate monitoring network (meetnetten.be) and there too we see many more losers (8) than winners (1)
A targeted expansion of the number of butterfly routes in Flanders is necessary to be able to calculate a reliable trend for the other (Red List) species as well. This would make us better able to keep our finger on the pulse of the butterflies and would enable us to adjust nature policy and management in Flanders more quickly.
