Climate change drives butterflies north

The latest Scottish Biodiversity Indicator, published by NatureScot today, examines the long-term trend for butterflies since 1979. The scientific report finds that, from 1979 to 2023, there has been an overall 35 percent increase across the 20 species analysed.

Generalist butterfly species, which use a range of habitats, have increased by half, while populations of specialist species, which are limited to specific habitats like heathland, remain stable.

Red admiral, orange tip and speckled wood butterflies have all seen the biggest population increases. Orange tip and speckled wood butterflies have increased three-fold, while there are almost ten times as many red admiral butterflies now compared to when records began in 1979.

But two species – grayling and small tortoiseshell – have suffered dramatic declines. Grayling is a coastal specialist whose 90 percent decline may be due to changes in habitat. Small tortoiseshell has dropped by more than 60 percent, with climate change, habitat loss and parasites thought to have affected these winged insects over the decades.

The research highlights that over the past 40 years, butterflies traditionally found south of the border - for example, orange-tip and peacock - have become more common in Scotland. But the potential for northward expansion is likely to be limited by habitat availability and local weather conditions that can affect their survival and dispersal.

NatureScot Trends and Indicators Analyst, Simon Foster, said:

“In recent decades, we’ve seen the damaging effects of climate change on butterflies, with species that fly in the spring emerging progressively earlier. But an earlier start to the butterfly season doesn’t necessarily benefit the insects if the plants and flowers they feed on die earlier than they used to.

“Extreme events, such as heavy rainfall and drought, can impact butterflies dramatically, and we see this reflected in how much their numbers vary from one year to the next. Butterflies generally benefit from warm, dry springs and summers, but drought conditions can reduce caterpillar food availability by reducing plant growth or shortening the flowering season. On the other hand, cold and wet weather can reduce butterfly activity and affect caterpillar growth and survival.

“As our climate becomes increasingly chaotic, it’s important we take steps now to protect our butterflies in the future. One way people can help is by joining the UK Butterfly Monitoring Scheme (UKBMS) and getting involved with surveys. It’s easy, fun and can help us improve our knowledge of what is happening where, giving us the best chance of targeting conservation measures most effectively.

“People can also help butterflies in their gardens by planting flowers that produce lots of nectar and pollen – there are ideas and tips on the Make Space for Nature pages of our website.”

Butterfly Conservation Head of Conservation for Scotland Tom Prescott said:

“We are delighted that generalist butterflies like the red admiral are doing so well in Scotland, but it’s deeply worrying that specialists like the grayling are not doing any better than 40 years ago - and some are doing much worse.

“It’s also crucial to remember that this data only shows how species are doing at sites where our fantastic UKBMS volunteers have been surveying, many of which are nature reserves. Across the UK, the distribution of our 58 native butterflies plummeted 42 percent from 1976 to 2019, and habitat specialists are doing the worst.

“We are doing targeted work in Scotland and across the UK to create and protect habitat for specialists, such as our project planting kidney vetch for the small blue with primary school pupils in the Highlands and working with farmers in Argyll to benefit marsh fritillary – but we still need to do a lot more to secure the future of our fantastic native species.”

Areas that are rich in butterflies and moths provide many benefits for people and nature, including pollination and natural pest control. Butterflies and caterpillars are also an important element in the food chain as prey for birds, bats and other animals.

As part of the Pollinator Strategy for Scotland, work is taking place across the country to improve habitat for pollinating insects. This includes creating nature networks to help wildlife move through a series of connected nature-rich areas. This helps their survival, ensures genetic diversity and increases their ability to adapt to pressures such as climate change. As well, farmers across Scotland are putting in place nature-friendly practices such as unsprayed field margins. These can help butterflies and other beneficial insects.

For species with specific habitat requirements, targeted action works best. The Species on the Edge project is helping to secure the future of some of Scotland’s most threatened butterflies including the northern brown argus and small blue butterfly. Volunteers and conservation organisations are working together to actively manage these butterfly habitats.

Pic credit: Small tortoiseshell by Iain H Leach Butterfly Conservation