Half of British butterflies placed on extinction Red List

Britain's butterflies face more threats than ever before, as the number of threatened species rises by more than a quarter.

The 2022 Red List of British butterflies, published by the charity Butterfly Conservation, classed five more species as threatened this year. This includes the scotch argus, which was classed as Vulnerable after its southerly ranges in northern England were reduced to just two sites.

However, the list found some cause for optimism, with the large blue butterfly, which went extinct in Great Britain just over 40 years ago, now classed as Near Threatened following a successful reintroduction project.

Dr Richard Fox, the head of science for Butterfly Conservation, says, 'Shockingly, half of Britain's remaining butterfly species are listed as threatened or Near Threatened on the new Red List. 

'Even prior to this new assessment, British butterflies were among the most threatened in Europe. While some species have become less threatened, and a few have even dropped off the Red List, the overall increase clearly demonstrates that the deterioration of the status of British butterflies continues apace.'

The findings of the Red List were published in the journal Insect Conservation and Diversity. 

What threats do butterflies face?

Butterflies and moths are both part of the order Lepidoptera, and are some of the most common animals in the world. In the UK, there are around 60 species, representing both species which live in the country year-round as well as seasonal migrants.

Their bright colours ensure that butterflies are one of the most recognised and documented groups of animals, which makes them a valuable indicator species to show when an ecosystem is under threat. 

Butterflies face a variety of pressures, mostly from habitat loss. In the UK, 80% of chalk grassland has been lost since 1945 which has slashed the number of rare plants which grow in these soils.

Dr Blanca Huertas, Senior Curator of Lepidoptera at the Museum, says, 'Butterflies are dependent on a specific set of factors in each stage of their lifecycle. As eggs and caterpillars, they are very sensitive to any changes in the microclimate and rely on certain plants.

'When they are adults, they are often more generalist, but modifying a habitat will take away plants that these butterflies depend on. This affects their ability to survive.'

As a result, the butterflies that depend on these plants have also been pushed into decline. Species such as the large tortoiseshell, which was once common to English woodlands, have been driven to extinction in the UK although they continue to survive in some areas of Europe.

Other threats facing butterflies include pollution, which affects their ability to navigate towards flowers, as well as climate change. Rising temperatures are causing butterflies to physically change, while their ranges are shifting north to remain within their preferred climate.

Specialist butterflies have been hit hardest by these threats, with 86% of the threatened or Near Threatened British butterflies depending on specific habitats. For northerly butterflies such as the large heath and northern brown argus, this has led to their ranges declining as they increasingly run out of suitable habitat to live in. 

This follows a similar pattern seen in dragonflies, where more northerly and specialist species are becoming more threatened as the climate changes. 

How can British butterflies recover?

While butterflies are under threat, the Red List demonstrates that there is the potential for a recovery. Alongside the large blue, the high brown fritillary and Duke of Burgundy have seen their populations stabilise as their conservation status is downgraded to less serious categories.

These butterflies have been the target of conservation programs aiming to restore and expand their habitats, providing refuges for the insects to survive. Projects such as Brilliant Butterflies, which works with local communities to restore chalk grassland, play an important role in this.

As well as restoring breeding habitats and other sites, it is also important to ensure connectivity between them. As butterflies cannot travel great distances in one go, this involves providing flower rich field margins that can act as stepping stones between habitat patches, as well as removing potential barriers.

These restoration efforts are supported by monitoring and genomic techniques to keep track of the health of the butterfly populations. These ensure that the populations can continue to grow, with interventions made if needed.

'We need a combination of scientific data from collections, such as those at the Museum, as well as monitoring data,' Blanca says. 'The collection data provides information about the past, and we have released over half a million records of British butterflies online. We need to continue to unlock this with support from researchers.

'Meanwhile, monitoring data tells us how butterflies are responding to modern changes. Going out to monitor butterflies takes a lot of effort, so community science initiatives, like those run by Butterfly Conservation, are really important to give us a wide range of data.'

As well as assisting with community science projects, individuals can also make a difference for butterflies in their homes. One way they can do this is by planting plants that are rich in nectar that can feed butterflies, as well as others that provide food for growing caterpillars.

Mowing less frequently and leaving patches of longer grass can also provide space for butterflies to lay their eggs.