Why are butterflies important? 

Butterflies are among the most threatened group of wildlife in the UK; the latest Red List assessment butterflies has revealed a 26% increase in the number of species threatened with extinction and a 76% decline in butterfly abundance or distribution since 1976.

Insects are extremely important for ecosystems and humans; insects, including butterflies, pollinate around 85% of our crops - providing a vital service worth billions of pounds globally. Butterflies are also bio indicators of a healthy environment and ecosystem - they are highly sensitive to changes in climate, pollution levels and harmful chemicals in the air. Butterflies are also important parts of the food chain- they are food for birds, bats and other insectivorous animals and parasites. They are excellent pollinators after bees and wasps - without these insects, we would have fewer plants!

This is due to habitat loss and fragmentation, as well as the climate crisis which is causing more extreme weather events and greater fluctuations in temperature. As the world's climate gets warmer and drier as a result of climate change, it is causing knock-on effects on British butterflies in the UK. July 2022 was seen as the driest July in the UK since 1935, with 2021 being one of the seven warmest years on record, with the average global temperature about 1.11°C above pre-industrial levels. 

How some species benefit from a warmer climate 

Butterflies have responded to climate change in many different ways. Some species have benefitted from the warmer weather, having expanded their ranges and colonised new sites further north. The comma is an example for this, it was once confined to the south-west and is now breeding in Scotland, spreading its range northwards at a rate of 10km a year. In addition to distribution changes, some butterflies are responding by emerging earlier in spring, which has positive benefits for some species by increasing their numbers and range.

All butterflies are ectotherms, meaning that they cannot generate their own body heat and are dependent on finding the optimal environmental conditions. Bigger and paler butterflies such as the large white and brimstone are among some of the species of insect which are best adapted to environmental temperature increases. This is because they angle their large reflective wings in relation to the sun and use them to direct the sun’s heat either away from, or onto their bodies. These species have either stable or growing populations.

However, more colourful species such as the Peacock and Red Admiral have greater difficulty controlling their body temperature, and smaller species like the small heath butterfly have even greater difficulty. Some species rely on finding a spot at a specific temperature within the microclimate of a landscape in order to control their body temperature. Some species such as the Brown Argus and small copper are “thermal specialists”, and have suffered larger population declines over the last 40 years.

How some species do not thrive in warmer climates  

Certain species such as the montane and the mountain ringlet have suffered, causing extinctions where sites have become too hot or dry. Many species are becoming threatened as they cannot move to keep pace with climate change now that their habitats are so small and fragmented. As temperatures are likely to rise by 4°C in the future, one quarter of Europe’s butterflies will lose 95% of their current range, leading to more extinctions. Also, the increase in temperature causes more frequent droughts, resulting in more butterfly species to dying out, in particular the specked wood which is more sensitive to drought. 

Caterpillars are also affected by climate change as when the plants that these caterpillars feed on die out, these larval butterflies either die or don’t grow as quickly. This means that climate change could wipe out the whole insect population. Also, because butterfly habitats are increasingly patchy and widely spaced out due to human land use, the likelihood of other butterflies coming in and recolonising an area has diminished.

Another fact is that some British butterflies are steadily getting bigger in response to climate change over the past few decades. This research was carried out using computer vision to analyse tens of thousands of butterfly specimens in the Natural History Museum’s collection. The findings of this study were that the adult butterfly body size increases with temperature during the late larval stages of development. 

What does the future hold for butterflies in Britain? 

It is not all bleak, we may see the return of species that long ago went extinct in Britain, such as black-veined white and large tortoiseshell. Successful re-introductions of large blue highlight that sites can be managed to boost numbers, and landscape-scale approaches help protect networks of sites. 

There are efforts to stop populations of cool-loving montane species, such as mountain ringlet becoming extinct. Local site management may help slow their decline, but reducing global temperature rises is also urgently needed as well as more drastic measures, such as translocating individuals to cool refuge locations, if they cannot get there themselves. More monitoring is also vital, to ensure early warning of populations at risk, buying us time to implement effective conservation management. 

The threat from climate change gives a sense of urgency to Butterfly Conservation’s strategy of conserving species at a landscape scale, making existing habitats bigger, better managed and more well connected. We need to make landscapes more diverse to help conserve many of our butterfly species. In nature reserves, some areas could be grazed or cut and others left standing. Also, within a garden lawn, patches of grass can be left to grow longer - these areas will provide cooler, shady places for many species of butterfly. 

Time is running out to save these beautiful insects, we need mitigate the effects of climate change and save these species as well as their habitats if we want future generations to enjoy them!

Sources:

• Butterfly Conservation (2022) Climate change and British butterflies
• Longdom Journals, J. Carrol (2021) Butterflies are bio indicators of a healthy environment and ecosystem
• Met Office (2022) Driest July in England since 1935
• University of Minnesota (2018) A warmer climate will also be a drier climate, with negative impacts on forest growth
• University of Southampton (2022) Britain's butterflies are getting bigger as the climate changes