Trillions of insects fly above the UK – but radar reveals night species are vanishing

27 October 2025.

A groundbreaking study has revealed that trillions of insects are flying over the UK every year — but night-flying species appear to be in worrying decline.

Researchers, led by the University of Leeds in collaboration with scientists at the Rothamsted Insect survey, analysed data from the country’s weather radar network. These Met Office radars traditionally track rainfall and storms but can be re-purposed to monitor flying and floating creatures. The team found that around 11 trillion arthropods — a group that includes insects and spiders — are aloft above Britain’s countryside and cities during daylight hours, with a further five trillion active after dark.

The findings, based on radar observations between 2014 and 2021 across more than 35,000 square kilometres, offer one of the most comprehensive pictures yet of the nation’s airborne insect life. They also highlight stark regional differences: over the study period insect numbers tended to rise in the south of England but fell sharply in the far north. 

While daytime species held steady, nocturnal arthropods — many of them vital pollinators or prey for bats and birds — showed an overall decline during the study period.

This study opens a window to a huge and important new source of biodiversity monitoring data. Our findings are just a tantalizing glimpse of what weather radar data can reveal for ecologists

The UK’s network of weather surveillance radars scan the sky hundreds of times a day. Historically this network had picked up data anomalies that were called ‘angels’ because radar operators didn’t know what they were. By the 1970s, however, it was clear that these were caused by birds, bugs and bats and were renamed ‘bioscatter’.

More recently, new radar technology that emits two different beams during a scan (known as "dual polarisation") and measuring how those signals are scattered back, has allowed researchers to tell insects apart from raindrops and estimate the number of insects flying between 500 and 700 metres above ground. 

The team found that both daytime and night-time insect abundance was higher in woodland, grassland and urban areas, but lower in farmland dominated by crops. Artificial light at night was also linked to reduced insect activity.

The study underscores growing concerns about the impact of light pollution, habitat loss and intensive agriculture on insects, which are essential to food webs and pollination.

Study co-author Dr Christopher Hassall of the University of Leeds said: “We’d like this research to contribute new insect metrics for the UK Government's biodiversity indicators, showing us how changes to landscape management affect insects.”

“This study opens a window to a huge and important new source of biodiversity monitoring data. Our findings are just a tantalizing glimpse of what weather radar data can reveal for ecologists,” added Dr Hassel

Co-author Professor James Bell, Professor of Entomology at Keele University and formerly head of the insect survey at Rothamsted, said the new application for weather radar gives researchers “an unprecedented opportunity” to understand the Earth’s diverse insects.

"For every human on planet earth, there are 1.4 billion insects of which we know almost nothing. Long-distance insect migration is often misunderstood, an essential but often obscured component of the life cycle of these small animals”

The new work supports Professor Bell’s previous findings, in collaboration with the Rothamsted Insect Survey, which revealed a 31% decline in nocturnal moth numbers between 1969 and 2016, partly driven by light pollution which profoundly alters their movement behaviour. 

Dr Lawrence Bramham, current head of the Rothamsted Insect Survey added, “This innovative approach, using weather radar for insect monitoring, presents exciting potential for future research. The Rothamsted Insect Survey (RIS) hosts a bespoke vertical looking entomological radar in collaboration with the University of Leeds paper authors. It is hoped that ongoing collaborations ground truthing radar data with RIS insect trapping, identification, UK-wide monitoring and associated entomological expertise may generate further impacts from these valuable technological developments.” 

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