Butterflies thrive in sunny weather. Yet global warming will not halt the decline in most species, says Michiel Wallis de Vries, entomologist and researcher for the Dutch Butterfly Association. 'Warming does have a slight positive effect, but it is not enough to reverse the downward trend for most species.'
Climate change is pushing the distribution areas of animals and plants further north. And it is going pretty fast: about 30 kilometres per year, according to Wallis de Vries. In other words, in ten years' time, Wageningen will have the climate Maastricht has now. Potentially, that could mean an extension of habitats, but that is theoretical. In practice, it does not tell us anything about how butterflies are distributed. Wallis de Vries therefore researched the influence of weather on butterfly populations. After all, warming also changes weather patterns. He compared the changes in the populations of 40 species of butterfly from year to year with the weather during the same periods. The correlations turned out to be complex. Wallis de Vries: 'Good weather during their flying phase makes populations grow. Butterflies become more active and lay more eggs. Long-term drought, on the other hand, has a negative effect. The hot dry summer of 2003 led to a bad butterfly year in 2004: the drought killed off the caterpillars.'
Wallis de Vries applied these correlations to climatic forecasts for the end of this century. The conclusions were not encouraging. 'The butterfly does not exist. But in general, most of the butterfly species will decline in numbers. Mobile species that do not make many demands on their environment, such as the old world swallowtail or the speckled wood butterfly, seem to be winners. But there are many more losers: the specialists that cannot cope with extremes, such as the grayling and the large chequered skipper.' Yet that is no reason to give up, says Wallis de Vries. With well-targeted management you can steer things in the right direction. 'You could bridge periods of drought by retaining water for longer in the landscape.'