One hundred years ago Flanders had 67 native species, of which 19 have disappeared, and 25 more are under threat. The main causes are fertiliser and pesticide use, the disappearance of many species of flowers, and the increasing fragmentation of the landscape.

The study was based on data collected between 1830 and 2010, with the majority of recent information from volunteers who report their sightings – not limited to butterflies – to the website www.waarnemingen.be. “With the help of this treasure-trove of information, we can not only see which species are currently present in Flanders, but also how their spread in the last ten years has changed, two important criteria in determining the chances of a species surviving,” a spokesman for the INBO said.

Comparison with the last survey in 1999 shows the negative trend is well-established: Four species died out between 1999 and 2003, and 12 species are worse off. “It is not for nothing that they call the Low Countries the most butterfly-unfriendly region in Europe,” the INBO said.