Scientists used Met Office Radar data has tracked trillions of insects flying over the UK for the first time, revealing an alarming decline in nocturnal species.
The team repurposed data from a UK network of 15 weather radars that scan the sky hundreds of times a day.
The analysis shows that between 2014 and 2021, daytime insect abundance remained relatively stable or even increased in southern regions, but nighttime airborne insect abundance generally declined, particularly in the far north.
“This is one of the first studies to show how diurnal and nocturnal flying insects are differentially exposed and how their habitat influences these patterns,” said Dr Mansi Manji, who led the work as a postdoctoral fellow at the University of Leeds and is now based at Azim Premji University in India. “This is an important step toward understanding where to focus conservation efforts.”
Modern radar works by sending out microwave pulses that bounce off precipitation and other airborne obstacles. By measuring the time it takes for the signal to return, its intensity and other characteristics, the radar can determine the location, number and size of insects in the air.
Their results show that an average of 11.2 trillion insects fly between 500 and 700 meters above the ground during the day, and just over 5 trillion at night. Insect numbers were higher in areas with forests, grasslands and even urban areas, but decreased in areas with intensive farming and high levels of artificial light.
Birds, bats and insects were first spotted as mysterious sightings by British military intelligence during the Second World War, with radar operators so baffled that the mysterious signals were initially known as “angels”.
Over the decades, as radar has come into use for weather forecasting, Met Office scientists have developed sophisticated algorithms to eliminate “biological scattering” caused by flocks of insects and migratory birds.
“They were throwing away a bunch of biodiversity data,” said Dr Christopher Hassall, an animal biology researcher at the University of Leeds and co-author of the study. “We realized that this data could potentially be extracted and that it could be a treasure trove of information rather than an annoyance.”
Instead, the team of insect mappers threw out the other half of the data—rain, clouds and weather—to reveal the insects' movements in the air.
“Some of the insects are active fliers, some simply follow thermal currents,” said Dr Ryan Neely from the National Center for Atmospheric Science and the University of Leeds. “It's an amazing way to visualize what the air is doing. It's really beautiful.”
The current study focused on total abundance rather than how many different species were present, which is often the focus of researchers. Citizen science monitoring of insect biodiversity.
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Nocturnal insects such as moths have shown an overall decline over the past four years, driven by declines in northern regions. The scientists concluded that artificial lighting at night, which is already known to disrupt insect behavior, may contribute to their decline.
“It may just be a glimpse, but there are also changes in the way we light the night, in terms of the types of light bulbs and car headlights getting brighter,” Hassall said.
Both during the day and at night, there was a decrease in the number of northern species and an increase in the number of insects in the south, which is likely due to the climate crisis.
“Northern species will decline because it gets too warm and dry for them,” Hassall said. “They will be replaced by southern species, but there is a lag.”
Insect abundance is higher in cities than in homogeneous agricultural lands, which are likely to offer less diverse habitat. The results were published in the journal Global Change Biology..
