Climate change could be disastrous for butterflies

By Mark Waghorn via SWNS

Climate change could spell disaster for butterflies, warns new research.

Longer and warmer autumns are making it harder for them to survive, say scientists.

Lab experiments found their chrysalises lose more weight and use more energy.

Lead author Dr. Matthew Nielsen, now at the University of Oulu, Finland, said: "We show stressful conditions experienced at one time of year can have lasting negative consequences at other times of year."

Green-veined whites - common across the UK - were exposed to conditions of varying temperature and length.

Those subjected to milder simulations fared best. Last autumn, Britain was hotter than the Algarve with temperatures reaching 24°C (75°F) at the end of September.

Dr. Nielsen said: "Climate change is making autumns warmer and last longer. It was this specific combination of conditions that had the greatest impact on the butterflies in our study."

The butterflies didn't die immediately under the more elevated conditions - but were less likely to turn into adults.

Once a caterpillar stops eating it hangs upside down from a twig or leaf and moults into a shiny chrysalis.

Within its protective casing it radically transforms - eventually emerging as a butterfly.

Dr. Nielsen said: "It links changes in one season to consequences in others."

Animals that enter a dormant stage through the winter are especially vulnerable to warming. It raises metabolism - causing them to run out of energy faster.

Dr. Nielsen explained: "Even though dormant animals use less energy than active animals, they use more when it is warmer, and they can't eat to replace that lost energy.

"It is already established that warmer winters are actually worse for dormant animals than colder ones. Our findings show warmer autumns are potentially even more dangerous."

The study was carried out at the University of Stockholm where he was formerly based.

In Sweden, the spring generation of green-veined white butterfly is usually the smallest because of the stress of winter dormancy.

Increased mortality after warmer and longer autumns could have a severe impact on abundance at a critical time of year.

Experts have warned some species in the UK face being wiped out by 2050. Butterflies are vital for the environment.

They are natural pest controllers and pollinators - feeding on the nectar of bright garden flowers and helping plants produce new seeds.

In the study, butterflies were exposed to temperatures as high as 25°C (77°F) for up to 16 weeks.

They already occur in southern parts of the butterflies' range - as far as Spain - and could happen further north under future climate change scenarios.

The timespan of dormancy before the onset of winter was not unreasonable. Some individuals can as much as two months earlier than others.

Groups of eight to 11 chrysalises were placed in chambers kept at 15, 20 or 25 °C for one to 16 weeks. All 459 chrysalises were then exposed to the same winter conditions for 24 weeks.

During the simulated autumn conditions, the researchers measured how much weight the chrysalises lost and how much energy they used.

Finally, they followed the butterflies' survival until they died or emerged as healthy adults during a simulated spring.

What is more, the conditions were constant rather than reflecting natural seasonal and daily variation.

These variations could further intensify the metabolic costs of autumn conditions, said the researchers.

They 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 added: "In our study we only considered survival to adulthood, but there could be even more negative effects later in life, for example on the ability to find mates or the number of eggs laid.

"Studying how warming in autumn, winter, and spring interact will also be key to understanding the actual impacts of climate change on dormant animals."

The study was published in the British Ecological Society journal, Functional Ecology.