The world's insect populations are plummeting everywhere we look

This is the conclusion published in a new paper in the journal Biological Conservation.

The review looked at 75 different studies covering a range of insect groups from around the globe, and the results are startling.

It has revealed that over 40% of all insects are declining, and a third are endangered. The data suggests that the rate of decline is at least 2.5% per year. According to the researchers' analysis, a quarter of insects could be wiped out within just a decade - although with so few insects populations having been studied, exact figures are hard to come by.

Specialist insects, while perhaps more sensitive to change, are not necessarily those most at risk. According to the study, all groups are on the decline, even common and generalist species which are often thought of as being more resistant to such disturbances.

Dr Gavin Broad, Principal Curator in Charge of Insects at the Museum, says, 'In a way it is logically inevitable that we are seeing these declines, as the habitats now remaining are so small and so fragmented compared to a century ago.

'There is just not the space for insects to live anymore.'

Underappreciated and overlooked

In recent years there has been a huge focus on the decline of birds and mammals, but less so for insects. Over 95% of all animals are invertebrates - they're the group that keep the world functioning.

'Insects are the main drivers of many of our ecosystems on land and in freshwater,' explains Gavin. 

They are the basis of many major food webs, forming the primary food source for birds, amphibians, fish and reptiles. They're also some of the most important pollinators of crops and significant organisms that cycle nutrients throughout the planet's terrestrial ecosystems.

Without insects, the environment would simply fall apart.

This is more than some hypothetical outcome: it is already being seen where the decline in insect populations have been studied.

Two years ago, it was reported that the biomass of flying insects in German nature reserves had fallen by three quarters. What's more, just last year one team found that ground insects in Puerto Rico had declined by 98%. 

While the problems in methodologies make it difficult to draw firm conclusions from both studies, one thing that stood out to the researchers in Puerto Rico was a lack of birds in the rainforest. Yet this dramatic drop in insects it is more than just a threat to other wildlife.

Without insects, there would be no crops for neither us nor our livestock to eat. The cycling of nutrients such as carbon and nitrogen through the ecosystems would stop. The environment would collapse and the threat to our future is difficult to understate.

The great unknown

Despite this latest paper being one of the most comprehensive analyses of the state of the world's insect populations, it still presents massive gaps. This is simply because not all insect groups have been studied equally. One order that is frequently overlooked is Diptera, or flies. 

Dr Erica McAlister, Senior Curator of Diptera at the Museum, says, 'Diptera have often been ignored, simply because they are difficult to study. It is really hard to identify the species from the larval stage, especially compared to other groups such as the moths and butterflies.

'When it comes to the Diptera around half of the larvae are aquatic, but what is interesting is that these are largely not mentioned in the aquatic ecosystem studies.'

The enormous biomass of flies supports a whole range of other animal groups, particularly the more traditionally charismatic birds and bats. This makes the fact that so little is officially known about the number and trend of flies all the more concerning.

According to Erica, this is a huge oversight. The Diptera, which include everything from houseflies and hoverflies to midges and mosquitoes, are hugely important largely down to their sheer numbers, although they are also significant contributors to most ecological function such as pollination. 

'We simply don't have enough empirical evidence for a lot of this,' explains Erica. 'Everyone definitely has a feeling that the numbers of flies is massively down and that we're not seeing what we saw in our childhood, but we need long-term studies to be really emphatic about this.

'The problem is that I don't think we have the time to do these anymore.'

There are also issues with the geographical scope of our knowledge of insects, but again this is down to the huge biases seen in existing studies.

'All these studies are massively northern temperate-biased, as the tropical studies are few and far between,' says Gavin. 'We've got an entire continent in Australia where the only study they could find is on the non-native honeybee.

'This paper has really highlighted how little we know about insects globally.'

A fragmented landscape

The research has not only looked into calculating the rate of the collapse, but has also tried to tease out what is driving these dramatic declines.  

The biggest threats are that of intensive agriculture and pollution in the forms of pesticides and fertilisers. As the human population grows there is an increase in the demand for both space and food. 

'The talk of agricultural intensification is not just pesticides,' explains Gavin. 'A lot of it is to do with uprooting hedgerows and producing huge monocultures which don't leave space for anything else.'

It is also down to expanding urbanisation and the fragmentation of surviving patches of habitat.

'That's one of the sad things, really,' says Gavin. 'It doesn't matter how much you protect a nature reserve - at the end of the day it is only one little island.'

In the tropical regions, however, climate change is emerging as a major threat to insect populations. Rainforests have largely been stable for a long time, meaning the insects that live there are very sensitive to change.

As these environments dry out while the climate warms, most species simply can't cope, so they die off.

What can be done?

On a fundamental level we need to further understand how and why these populations are crashing, but time is against us.

One of the easiest fixes, in the short term at least, could be to reverse the land-use change that has swept the countryside. Restoring the wildflower-rich meadows, and managing those that still exist, could help mesh the patchwork of protected habitat that has survived.

There is also a real obligation to inspire the next generation's understanding of the environment, and more significantly the vital role played by insects in underpinning it all. 

'I think we need better education in schools,' says Erica. 'We need to get people to look at insects and appreciate them. There is still such a bias - even within science - towards the vertebrates, even though most of the ecosystem's function is down to the insects.'

But there also needs to be a change in how we see insects as a whole.

'We really need a shift change in how we report these things and the language we use,' explains Erica. 'These subjects are always buried in the news because they can be depressing stories, but we can't just ignore them.'

The paper's authors say the answer is radical change in the way we live, particularly the way we produce food. They say we ought to replace pesticides with more sustainable crop-growing practices.

Otherwise, they concluded, 'insects as a whole will go down the path of extinction in a few decades.

'The repercussions this will have for the planet's ecosystems are catastrophic to say the least.'