Marbled White - Rob Blanken

Only 12 hours after Sir David Attenborough explained the personal and scientific benefits of Big Butterfly Count to the watching nation, I was standing under a tree in the pouring rain.

In a typical British summer, I would have viewed this as some kind of curse – no rain for weeks then just as Big Butterfly Count begins the long, hot spell of settled weather collapses into the cool, rainy conditions that have blighted many previous Counts. But this year I was delighted to see the rain, for two reasons: first, reassuringly, the weather forecasters seemed certain that the hot, sunny conditions would rapidly return over the weekend so the counting would not be scuppered, and second, and critically for the butterflies, drought is a killer.

The glorious sunshine is perfect for adult butterflies to get on with their lives, finding mates, visiting flowers, dispersing to new areas and, most importantly, laying eggs. Their offspring, the caterpillars that will hatch in the next few weeks, will need fresh green plants on which to feed – if the plants have withered and died in the drought, then caterpillars will starve and the next generation of butterflies will be much reduced.

This was seen very clearly after the famous 1976 drought. 1976 itself was a great year for butterflies, but the long drought, which had its origins back in 1975, took a heavy toll on this butterfly bonanza and numbers crashed the following year. The wider countryside species, those butterflies that we encounter in gardens, parks and the farmed countryside, didn’t fully recover until 1984, while the specialist butterflies, those that require particular nature-rich habitats such as chalk grassland or heathland, have never recovered from the double whammy of the drought and the large-scale destruction of such habitats that was rife in that era.

A recent study led by York University examining extreme population changes for 207 butterfly and moth species in England since the 1960s, found that the highest number of population crashes occurred in 1977, when 54 species (26% of those studied) underwent severe declines, clearly linked to the drought. Many more species will have undergone less-extreme declines too.

Similarly, in 1995, which was the driest UK summer since records began in 1776, the drought also had a significant impact on butterflies. This time, however, overall butterfly numbers did not crash in the following year, perhaps because the drought was shorter in duration than in 1976. Nevertheless, some common butterflies, all of which are among the target species for Big Butterfly Count, were badly affected. A study by the Centre for Ecology & Hydrology showed that transect counts of the Large White, for example, fell by an average of 66% between 1995 and 1996, while those of Small White decreased by 56% on average, Ringlet by 51%, Green-veined White by 45% and Speckled Wood by 41%.

So, while the hot, dry weather this summer is good for adult butterflies and, anecdotally, they do seem to be around in better numbers, some rain is very welcome to alleviate drought and ensure the survival of the next generation. By taking part in Big Butterfly Count, from now until 12th August, you’ll be helping us to assess how this year’s weather is influencing butterfly numbers. Take part at www.bigbutterflycount.org

Richard Fox

Associate Director Recording and Research, Butterfly Conservation

@RichardFoxBC