Why the UK’s butterflies are booming in 2025

Biodiversity is rapidly declining, through the United Kingdom and in the world. Butterflies are excellent to help us understand these changes. Where the butterfly communities are rich and diverse, the ecosystem is also. But the opposite is also true: if the number of butterflies is low and there are few species, it is a bad sign for the global variety and the abundance of life in the region.

Butterfly observations were among the lowest ever recorded in the United Kingdom in 2024 – a low point in a downward trend that was documented in North America and elsewhere.

Last year, the low figures in the United Kingdom were probably due to the weather – especially in summer, especially cloudy and humid. These are not ideal conditions for butterflies, which use the heat of the sun to regulate their temperature and (especially) do not fly in the rain.

Although the weather conditions vary, climate change makes unpredictable weather conditions more common. Wildlife is under the immense combined pressure of loss and climate change of housing, and it leads many species to extinction. Consecutive summers with bad weather can push butterflies and other species on the edge.

Fortunately for butterflies, 2025 has been a striking contrast – so far. After the driest spring since 1893 and several waves of heat at the beginning of summer in the United Kingdom, butterflies rebounds really in a lot of sun, which keeps them active.

The legendary legendary legendary lepidopterist Chris Van Sway of Butterfly Conformation Europe publishes the results of the Dutch butterfly accounts from the beginning of spring to the end of autumn. Many of these “transect surveys”, which involve the recording of butterflies while following a straight line through a habitat, have been repeated in the same places over several decades. As such, they give reliable trends in the diversity and abundance of butterflies.

Van Sway notes that many common species have an excellent year. Many white species, including the big white, small white and green white, are doing particularly well. Peacock butterflies are also recorded on these Dutch transects in some of their best figures in the past 20 years. These trends are probably the same in the United Kingdom.

In the Knepp area in the West Sussex, a farm that underwent a reset in 2001, biologists report a record number not only from butterflies in general, but the elusive and amazing purple emperor (Apatura Iris). This species can only survive in old and large woods with willows on which they lay their eggs. Because they live almost exclusively in the canopy, they are often difficult to see.

It is a treat to even see a purple emperor, and Knepp has recorded his figures since 2014. The previous record was 66 over the summer in 2018 (another warm and sunny). But the figures for 2025 broke this, with a total of July 80 to 11.

I have the pleasure of often working in a meadow next to a river, and the numbers of butterflies are astounding here compared to 2024. Even the Buddleia Bush outside my office has had at least 30 butterflies at the same time, a wide variety of common species, in recent weeks – an absolute joy to see.

Hot weather helps butterflies – until it is not

It looks like good news, right? The butterflies were saved and we had nothing to do. I would be happy even if it put me out of a job, and although it ignores the incredible work of charitable organizations such as the conservation of butterflies. But this is of course not the whole story.

Our standard for what is an excellent year for butterflies has been considerably reduced due to the extent of the loss during decades and centuries. The big summer of butterfly that we have could be comparable to a horrible year 30 years ago. Likewise, this warm and dry weather is good for a while, but if he does not start to rain soon, the plants will wither.

As we saw during the intense heat wave of summer 2022. The two plants that the butterfly larvae use for the food and the sources of adult butterflies were so stressed by the lack of precipitation that they failed to help adults and caterpillars.

The exceptionally hot spring of 2025 led to butterflies emerging from hibernation (called “wintering” when it concerns insects) unusually.

Butterflies winter in eggs, caterpillars or adults. Their emergence is generally triggered by the increase in temperatures, and the heat of this year seems to have accelerated this process: 21 of the 33 species of butterflies in the Dorset were identified earlier than usual. The dull skipper (Erynnis Tages), an unpretentious and increasingly rare species, emerged a whole month earlier than usual.

Although the first observations may seem encouraging, they raise concerns. If plants do not also respond to warmer temperatures while flowering earlier, there may not be enough food to support these first butterflies and other pollinating insects. This is an increasing concern as the global climate is changing.

Overall, there are reasons to be delighted with the summer of 2025. The sunny time has allowed a vital boom in number of butterflies, despite the constant tension that nature is under. It is refreshing to see a bush full of lively and beautiful insects.

However, the rain is still necessary, and the swing between a very humid year in 2024 and the potential of very dry in 2025 indicates violent violence by climate change of weather conditions on which nature has long depends.

You can support the conservation of butterflies by mowing less your lawn, planting more native flowers and joining the annual number of annual butterflies from the United Kingdom – which begins on Friday July 18 – to report your observations and help experts like me follow.

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