An image of a silver spotted skipper taken as part of the iCollections project

Silver spotted skipper specimen data is being digitised as part of the Museum's iCollections project.

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Butterflies unlocking our climate's secrets

Climate change is having a dramatic effect on the lives of British butterflies - they are emerging earlier, changing in size and living in new habitats.

Museum researchers Steve Brooks and Dr Angela Self used digitised collections to track the changes native butterfly species have experienced over the last 140 years of unprecedented temperature fluctuations in Britain.

British summers are getting warmer and our springs are blooming earlier, often bringing mild temperatures and blue skies as early as February.

The complex lifecycles of butterflies rely on delicate balances within the ecosystem, including heat and availability of food.

Tracking their habits can reveal important lessons about the state of the environment.

An image of a silver-spotted skipper on a flower

Silver-spotted skippers have a larger wingspan when summers are warmer.

According to Met Office data, average UK temperatures increased by 0.6°C between 1870 and 1970, and since then have increased even more rapidly, going up by 1.5°C in the last 40 years. This change is in part down to rising levels of carbon dioxide and other gases in the atmosphere, which has created a greenhouse effect.

The Museum's collections contain data on British butterflies stretching back beyond the nineteenth century - a valuable tool for researchers hoping to uncover long-term trends in our changing ecosystems.

Data at the click of a button

This data is now online for the first time thanks to the Museum's iCollections project, meaning Steve Brooks had access to 180,000 butterfly specimens on his desktop.

With Dr Phil Fenberg, a colleague at Southampton University, Brooks and Dr Self have been examining the lifecycle, size and distribution of the silver-spotted skipper, a butterfly that is most at home in short chalk grassland in the south of England.

It is well-suited to the study of climate change due to its annual reproductive cycle and habitat.

The researchers found that in warm summers the butterfly is larger and flies earlier in the year.

A scientist digitising a specimen

Museum scientists are digitising one specimen every 2.9 minutes.

Brooks said: 'Looking at how species respond to temperature is essential for understanding the ecological and evolutionary consequences of climate change.

'Our study would not be possible without data from digitized collections paired with monthly temperature records.'

Why does temperature matter?

It was found that in the years when Britain experienced warm June temperatures, the adult male skippers had larger wings, and in warm Julys both sexes emerged from their chrysalises earlier.

Brooks said: 'Caterpillars are in their final growing stage in June, so warmer environments could mean they can grow faster and may be getting better quality food.

'In July the adult butterflies develop in the chrysalis and emerge earlier when it is warmer.

'And the butterflies are on the wing in August, so warm Augusts mean they could venture further north than before.

'Our study has shown these three responses to climate change together for the first time in a single species.'

An image of a silver-spotted skipper

Investigations into silver-spotted skippers help scientists to understand the effects of climate change.

More studies are still being done on the other British butterfly species, to find out which are emerging earlier, getting larger and expanding their homes in the north of the country.

Butterflies that were previously restricted to the south of England are expected to expand their range as the climate changes.

Breaking the rules

Bergmann's rule, named after nineteenth-century German biologist Carl Bergmann, states that as temperatures increase, organisms get smaller.

This is because warm temperatures allow the metabolic rate of living things to speed up, meaning they need more food to achieve and maintain large body sizes.

The work has demonstrated the silver-spotted skipper goes against this rule, probably because the species produces one generation each year. This means it has longer to grow than species that produce several generations each summer.

Understanding climate change

Brooks' investigations into the changing lives of butterflies are helping scientists to understand how warmer global temperatures are affecting species in Britain.

He said: 'This work would have been impossible without access to the digital collections of British species, allowing us to examine large amounts of data.

'Changes in butterfly size and habit will help us to understand the wider effects of global climate change on British organisms and ecosystems.'