Butterflies face struggle for survival due to climate change

Butterflies are one of the fixtures of the British garden – in the spring and summer, it’s a wonderful sight to see them fill up the skies with colour. In my garden, we have a Buddleia that attracts hundreds of butterflies each year, and it’s amazing to watch them all on the blossoms. But it seems that the impact of climate change could make those experiences a thing of the past. According to research published in Functional Ecology, the ensuing warmer, longer autumns may reduce the number of butterflies that emerge the following spring.

Researchers at Stockholm University, the University of Oulu, and Greifswald University explored the potential impact of climate change on butterflies. They focused on the green-veined white butterfly, a species that is common throughout the UK and Europe, and exposed their chrysalises to simulated autumn conditions of varying temperature and length (between one and 16 weeks), followed by a 24-week period of simulated winter. Those chrysalises exposed to warmer and longer autumn conditions lost more weight and used more energy – although they didn’t die immediately, the butterflies that experienced these conditions were less likely to survive to adulthood the following spring.

The Chrysalis is the pupal stage of the butterfly, and it provides protection and a space for a caterpillar to mature into a butterfly. Shortening daylight hours in the autumn causes the pupae – or chrysalises – of some butterfly species to enter a dormant state that enables them to avoid harsh winter conditions. At the end of winter, these pupae exit the dormant state and continue to develop before emerging as butterflies. However, the team found that chrysalises kept in warmer conditions for longer had a higher metabolic rate and thus used more energy (losing weight in the process). Researchers suggested that the mortality rate was probably linked to the reduced energy reserves.

Dr Matthew Nielsen at the University of Oulu, who conducted the research at Stockholm University, said: “Climate change is making autumns warmer and last longer, and it was this specific combination of conditions that had the greatest impact on the butterflies in our study.We show that stressful conditions experienced at one time of year can have lasting negative consequences at other times of the year, linking changes in one season to consequences in others.” There are certain limits to extrapolating these conclusions out to wider butterfly populations. It all took place in a lab following a single species, and the simulated conditions were constant, rather than reflecting natural seasonal and daily variation. However, the researchers suggested that these could actually intensify the metabolic costs of autumn conditions, leading to an even greater reduction in the butterfly population.

We show that stressful conditions experienced at one time of year can have lasting negative consequences at other times of the year, linking changes in one season to consequences in others

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–Dr Matthew Nielsen at the University of Oulu

The researchers are now looking to explore the impacts of a warming climate on butterflies in more detail and look at the effects of multiple seasons. Dr Nielsen said: “The potential impact here is double-pronged and highly significant. Most immediately, the rising temperatures could reduce the population numbers of butterflies, maybe pushing them to endangered levels or even extinction.Just as human activity may impact butterfly numbers, the reduced butterfly numbers may go on to hurt humans.Climate change is causing issues for insects across the board, and it looks like the range of insects is going to shrink quite dramatically.”

Just as human activity may impact butterfly numbers, the reduced butterfly numbers may go on to hurt humans.

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–Dr Matthew Nielsen at the University of Oulu

The world needs insects, and if climate change is reducing their populations, that’s something we need to worry about.