The summer of 2013 is the best butterfly year of the century so far, according to figures from the Vlinderstichting foundation.

While it is hard to calculate how many butterflies there have been, the foundation’s volunteers say they have seen some 40% more butterflies in fixed observation sites than in other years.

The cold winter and late, wet spring encouraged vegetation to grow, ensuring abundant food for caterpillars, the foundation said. And the sunshine in June allowed butterflies themselves to flourish in optimum conditions.

Nevertheless, butterflies are still having a tough time, and this year would have been considered normal in terms of butterfly numbers in the 1990s, the foundation said.