A chalkhill blue butterfly on a purple scabious

Butterflies such as the chalkhill blue are among the flying insects which are thought to have declined in the past 20 years. Image © Shutterschock/Shutterstock

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UK's flying insects have declined by 60% in 20 years

The UK's insect population has fallen sharply as the invertebrates are affected by rising temperatures and fragmented habitats.

While the declines are dramatic, small changes to our homes and gardens can play a significant part in bringing them under control.

The UK's flying insect population has declined by as much as 60% in the last 20 years, a new study has revealed.

Conservation charities Buglife and the Kent Wildlife Trust asked members of the public to count the number of insects splatted against their vehicle numberplates, and compared this to a similar study from 2004. They found that counts were down the most in England, where 65% fewer insects were recorded, and the least in Scotland, which recorded a 28% fall.

Paul Hadaway, the director of conservation at Kent Wildlife Trust, says, 'The results from the Bugs Matter study should shock and concern us all. We are seeing declines in insects, which reflect the enormous threats and loss of wildlife more broadly across the country.

'These declines are happening at an alarming rate and without concerted action to address them we face a stark future. Insects and pollinators are fundamental to the health of our environment and rural economies.

'We need action for all our wildlife now by creating more and bigger areas of habitats, providing corridors through the landscape for wildlife and allowing nature space to recover.'

The study provides further evidence that insects are in peril around the world, with a 2019 study suggesting that the invertebrates are declining by at least 2.5% every year.

Dr Gavin Broad, the Principal Curator in Charge of insects at the Museum, says, 'The results of this study are not surprising. Evidence of insect declines has been available for some time, particularly in certain regions of the world.

'If we knew why insects were declining, it could help protect other animals. For instance, declines in woodland birds may relate to the loss of insects in these habitats as they could be losing prey. Alternatively, they could be responding to the same habitat and climactic changes in similar ways. But until we understand both groups, it's hard to tell.'

A red cacao tree with pods hanging from its branches

The cacao tree, from which chocolate is made, is almost entirely dependent on insect pollination. Image © TigerStocks/Shutterstock

Which insects are declining, and why?

The decline in insects affects all the major groups. In the next few decades, as many as 40% of the world's species could become extinct, including bees, ants and butterflies.

These insects represent some of the most significant pollinators of plants. While plants are pollinated in many different ways, insect-pollinated crop plants such as apples, pears, cucumbers, watermelons and almonds, will become significantly less productive without pollinators, and could fail altogether.

Even our sweet tooth could be affected, with pollinators essential for the production of cocoa beans and vanilla pods.

The impact of insect loss goes far beyond our food supplies, however, as animals such as birds which depend on them for food will also be hit.

Meanwhile, the ecosystem services insects provide will also be struck. This could see dead plants and animals pile up if insects and their larvae aren't around to consume them, while piles of poo could become more prevalent if dung beetles aren't around to process it.

The major causes of these declines are believed to be related to agriculture. The use of pesticides and fertilisers is killing insects, while the conversion of meadows, woodland and hedgerows into pasture and fields is also having a damaging effect.

Our demand for certain crops is also a threat to insects, with large areas growing just a single type of plant, known as a monoculture, leaving less of a variety of food for most insects to feed and thrive on.

Other factors, including air pollution and climate change, are also thought to be contributing to the ongoing insect population crisis.

Insects splatted on the front bumper and numberplate of a car

Insects recorded on numberplates were used to estimate the decline. Image © Lost_in_the_Midwest/Shutterstock

What has research into insect declines found?

The study asked members of the public to clean their front numberplate before going out for a drive, using a 'splatometer' (a standardised grid) to ensure that the same area of every numberplate was being observed.

These community scientists were then asked to record the route of their journey, as well as the number of insects in the grid area at the end of their drive.

The study found that between an initial survey in 2004, and the follow-up in 2021, counts had declined by 58.5% on average, suggesting flying insect abundance could be declining by over a third per decade.

The results follow a similar pattern to a study conducted annually in Denmark, where insects splatted on car windscreens are counted, and ties into a recent report from Rothamsted Research which demonstrated that moths had almost halved in abundance in the UK's woodlands in the past 50 years.

However, the methodology of the Bugs Matter report means that its data alone is not enough to draw a clear trend.

'While the report is concerning, the sample size was not as large as it could be, which makes it difficult to compare different regions,' Gavin adds. 'It also doesn't account for habitat type, which has a significant effect on flying insect abundance.'

The decline may also not directly relate to a loss of abundance, but the result of flying insects adapting to changing climates and habitat fragmentation. A study of the orange-tip butterfly found that males were growing smaller to focus on a host plant which was patchily distributed, while insects such as wasps have grown smaller in response to climate change.

This would make them less able to cross barriers such as roads as it would increase the effort it would take, and as a result make these insects less prominent in the study.

Find out how to make your own log pile with this short video

How can I halt insect declines?

While insects may be under threat, they remain the most diverse and abundant animals in the world. If we give them an opportunity to recover, then there is every chance they will rebound strongly.

'The obvious step to halt insect declines is to manage habitats in a way which supports them,' Gavin says. 'Even small patches of habitat can host large populations of insects if they're well managed, so it's important that there is enough habitat for insects and that it's joined up. A similar strategy for wetland birds has helped them rebound, so it can work for insects too.

'The other issue in stopping these declines is a lack of research. While we have some ideas, the exact mechanisms are not entirely certain. Research into the plants that insects depend on, and how this flora will be affected by topics such as climate change, is also lacking.'

Using natural history collections, such as those held by the Museum, can help provide a baseline of how insect populations were in the past, and how they have changed over time. Studies are beginning to unlock this information to help us tackle the challenges facing insects today.

Outside of research, there are a variety of steps that everyone can take to support insects. Growing insect-friendly plants in gardens and even window boxes can help provide food for pollinators and other invertebrates.

If you have a garden, cutting your grass less is another way to make the world to be more insect-friendly. Not only does this save time and effort, but it promotes the growth of wildflowers that pollinators and other insects depend on.

Giving over an area of your garden to long grass can provide space for insects to lay their eggs, and shelter from predators. Creating log piles can help protect beetles, as well as adding nutrients to the soil.

It's also important that we understand how insect populations continue to change. Taking part in community science projects such as Bugs Matter can help keep track of the unprecedented ways in which our world is changing.

You can find out more about the Bugs Matter survey, and how to get involved, here.