Insects could vanish within a century at current rate of decline, says global review
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| The rate of insect extinction is eight times faster than that of mammals, birds and reptiles. Photograph: Courtesy of Entomologisher Verein Krefeld |
The world’s insects are hurtling down the path to extinction,
threatening a “catastrophic collapse of nature’s ecosystems”, according
to the first global scientific review.
More than 40% of insect species are declining and a third are endangered, the analysis found. The rate of extinction is eight times faster than that of mammals, birds and reptiles. The total mass of insects is falling by a precipitous 2.5% a year, according to the best data available, suggesting they could vanish within a century.
The planet is at the start of a sixth mass extinction in its history, with huge losses already reported in larger animals that are easier to study. But insects are by far the most varied and abundant animals, outweighing humanity by 17 times. They are “essential” for the proper functioning of all ecosystems, the researchers say, as food for other creatures, pollinators and recyclers of nutrients.
Insect population collapses have recently been reported in Germany and Puerto Rico, but the review strongly indicates the crisis is global. The researchers set out their conclusions in unusually forceful terms for a peer-reviewed scientific paper: “The [insect] trends confirm that the sixth major extinction event is profoundly impacting [on] life forms on our planet.
“Unless we change our ways of producing food, insects as a whole will go down the path of extinction in a few decades,” they write. “The repercussions this will have for the planet’s ecosystems are catastrophic to say the least.”
The analysis, published in the journal Biological Conservation, says intensive agriculture is the main driver of the declines, particularly the heavy use of pesticides. Urbanisation and climate change are also significant factors.
“If insect species losses cannot be halted, this will have catastrophic consequences for both the planet’s ecosystems and for the survival of mankind,” said Francisco Sánchez-Bayo, at the University of Sydney, Australia, who wrote the review with Kris Wyckhuys at the China Academy of Agricultural Sciences in Beijing.
The 2.5% rate of annual loss over the last 25-30 years is “shocking”, Sánchez-Bayo told the Guardian: “It is very rapid. In 10 years you will have a quarter less, in 50 years only half left and in 100 years you will have none.”
One of the biggest impacts of insect loss is on the many birds, reptiles, amphibians and fish that eat insects. “If this food source is taken away, all these animals starve to death,” he said. Such cascading effects have already been seen in Puerto Rico, where a recent study revealed a 98% fall in ground insects over 35 years.
The new analysis selected the 73 best studies done to date to assess the insect decline. Butterflies and moths are among the worst hit. For example, the number of widespread butterfly species fell by 58% on farmed land in England between 2000 and 2009. The UK has suffered the biggest recorded insect falls overall, though that is probably a result of being more intensely studied than most places.
Bees have also been seriously affected, with only half of the bumblebee species found in Oklahoma in the US in 1949 being present in 2013. The number of honeybee colonies in the US was 6 million in 1947, but 3.5 million have been lost since.
There are more than 350,000 species of beetle and many are thought to have declined, especially dung beetles. But there are also big gaps in knowledge, with very little known about many flies, ants, aphids, shield bugs and crickets. Experts say there is no reason to think they are faring any better than the studied species.
A small number of adaptable species are increasing in number, but not nearly enough to outweigh the big losses. “There are always some species that take advantage of vacuum left by the extinction of other species,” said Sanchez-Bayo. In the US, the common eastern bumblebee is increasing due to its tolerance of pesticides.
Most of the studies analysed were done in western Europe and the US,
with a few ranging from Australia to China and Brazil to South Africa,
but very few exist elsewhere.
“The main cause of the decline is agricultural intensification,” Sánchez-Bayo said. “That means the elimination of all trees and shrubs that normally surround the fields, so there are plain, bare fields that are treated with synthetic fertilisers and pesticides.” He said the demise of insects appears to have started at the dawn of the 20th century, accelerated during the 1950s and 1960s and reached “alarming proportions” over the last two decades.
He thinks new classes of insecticides introduced in the last 20 years, including neonicotinoids and fipronil, have been particularly damaging as they are used routinely and persist in the environment: “They sterilise the soil, killing all the grubs.” This has effects even in nature reserves nearby; the 75% insect losses recorded in Germany were in protected areas.
The world must change the way it produces food, Sánchez-Bayo said, noting that organic farms had more insects
and that occasional pesticide use in the past did not cause the level
of decline seen in recent decades. “Industrial-scale, intensive
agriculture is the one that is killing the ecosystems,” he said.
In the tropics, where industrial agriculture is often not yet present, the rising temperatures due to climate change are thought to be a significant factor in the decline. The species there have adapted to very stable conditions and have little ability to change, as seen in Puerto Rico.
Sánchez-Bayo said the unusually strong language used in the review was not alarmist. “We wanted to really wake people up” and the reviewers and editor agreed, he said. “When you consider 80% of biomass of insects has disappeared in 25-30 years, it is a big concern.”
Other scientists agree that it is becoming clear that insect losses are now a serious global problem. “The evidence all points in the same direction,” said Prof Dave Goulson at the University of Sussex in the UK. “It should be of huge concern to all of us, for insects are at the heart of every food web, they pollinate the large majority of plant species, keep the soil healthy, recycle nutrients, control pests, and much more. Love them or loathe them, we humans cannot survive without insects.”
Matt Shardlow, at the conservation charity Buglife, said: “It is gravely sobering to see this collation of evidence that demonstrates the pitiful state of the world’s insect populations. It is increasingly obvious that the planet’s ecology is breaking and there is a need for an intense and global effort to halt and reverse these dreadful trends.” In his opinion, the review slightly overemphasises the role of pesticides and underplays global warming, though other unstudied factors such as light pollution might prove to be significant.
Prof Paul Ehrlich, at Stanford Universityin the US, has seen insects vanish first-hand, through his work on checkerspot butterflies on Stanford’s Jasper Ridge reserve. He first studied them in 1960 but they had all gone by 2000, largely due to climate change.
Ehrlich praised the review, saying: “It is extraordinary to have gone through all those studies and analysed them as well as they have.” He said the particularly large declines in aquatic insects were striking. “But they don’t mention that it is human overpopulation and overconsumption that is driving all the things [eradicating insects], including climate change,” he said.
Sánchez-Bayo said he had recently witnessed an insect crash himself. A recent family holiday involved a 400-mile (700km) drive across rural Australia, but he had not once had to clean the windscreen, he said. “Years ago you had to do this constantly.”
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More than 40% of insect species are declining and a third are endangered, the analysis found. The rate of extinction is eight times faster than that of mammals, birds and reptiles. The total mass of insects is falling by a precipitous 2.5% a year, according to the best data available, suggesting they could vanish within a century.
The planet is at the start of a sixth mass extinction in its history, with huge losses already reported in larger animals that are easier to study. But insects are by far the most varied and abundant animals, outweighing humanity by 17 times. They are “essential” for the proper functioning of all ecosystems, the researchers say, as food for other creatures, pollinators and recyclers of nutrients.
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| Scarce copper butterflies. Photograph: Marlene Finlayson/Alamy Stock Photo/Alamy |
Quick guide
Insect collapse: the red flags
Butterflies and moths
There has been a “severe reduction” in butterflies and moths
in the Kullaberg Nature Reserve in Sweden compared to 50 years ago.
Scientists found over a quarter of the 600 species once found had been
lost. Butterflies were hardest hit, losing almost a half of species,
including the large tortoiseshell and scarce copper. In England, two-thirds of 340 moth species declined from 1968-2003.
Bumblebees
Museum records enabled scientists to assess the fate of 16 species of bumblebees
in the US midwest from 1900 to 2007. They found four had completely
died out, while eight were declining in number, and blamed intensive
agriculture and pesticides.
Dragonflies
Red dragonfly populations have fallen sharply in Japan since the
mid-1990s, which scientists link to insecticides in rice paddies that stop the water-living nymphs emerging into adults. In the US, recent surveys across California and Nevada found 65% of dragonflies and damselflies had declined in the 100 years since 1914.
Leafhoppers
Leafhoppers and planthoppers often make up a large proportion of the
flying insects in European grasslands. But scientists found their
abundance in Germany plunged by 66% in the 50 years to 2010. Soil acidification, partly due to heavy fertiliser use, was the main cause.
Ground beetles
In the UK, dramatic declines in ground beetles
have been seen in almost three-quarters of the 68 carabid species
studied from 1994-2008. A few species increased, but overall one in six
of all the beetles was lost in that time.
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“Unless we change our ways of producing food, insects as a whole will go down the path of extinction in a few decades,” they write. “The repercussions this will have for the planet’s ecosystems are catastrophic to say the least.”
The analysis, published in the journal Biological Conservation, says intensive agriculture is the main driver of the declines, particularly the heavy use of pesticides. Urbanisation and climate change are also significant factors.
“If insect species losses cannot be halted, this will have catastrophic consequences for both the planet’s ecosystems and for the survival of mankind,” said Francisco Sánchez-Bayo, at the University of Sydney, Australia, who wrote the review with Kris Wyckhuys at the China Academy of Agricultural Sciences in Beijing.
The 2.5% rate of annual loss over the last 25-30 years is “shocking”, Sánchez-Bayo told the Guardian: “It is very rapid. In 10 years you will have a quarter less, in 50 years only half left and in 100 years you will have none.”
One of the biggest impacts of insect loss is on the many birds, reptiles, amphibians and fish that eat insects. “If this food source is taken away, all these animals starve to death,” he said. Such cascading effects have already been seen in Puerto Rico, where a recent study revealed a 98% fall in ground insects over 35 years.
The new analysis selected the 73 best studies done to date to assess the insect decline. Butterflies and moths are among the worst hit. For example, the number of widespread butterfly species fell by 58% on farmed land in England between 2000 and 2009. The UK has suffered the biggest recorded insect falls overall, though that is probably a result of being more intensely studied than most places.
 |
| Surveying butterflies in Maine, US. Photograph: Shawn Patrick Ouellette/Getty Images |
There are more than 350,000 species of beetle and many are thought to have declined, especially dung beetles. But there are also big gaps in knowledge, with very little known about many flies, ants, aphids, shield bugs and crickets. Experts say there is no reason to think they are faring any better than the studied species.
A small number of adaptable species are increasing in number, but not nearly enough to outweigh the big losses. “There are always some species that take advantage of vacuum left by the extinction of other species,” said Sanchez-Bayo. In the US, the common eastern bumblebee is increasing due to its tolerance of pesticides.
 |
| Guardian graphic. Source: Sánchez-Bayo & Wyckhuys, Biological Conservation, 2019 |
“The main cause of the decline is agricultural intensification,” Sánchez-Bayo said. “That means the elimination of all trees and shrubs that normally surround the fields, so there are plain, bare fields that are treated with synthetic fertilisers and pesticides.” He said the demise of insects appears to have started at the dawn of the 20th century, accelerated during the 1950s and 1960s and reached “alarming proportions” over the last two decades.
He thinks new classes of insecticides introduced in the last 20 years, including neonicotinoids and fipronil, have been particularly damaging as they are used routinely and persist in the environment: “They sterilise the soil, killing all the grubs.” This has effects even in nature reserves nearby; the 75% insect losses recorded in Germany were in protected areas.
 |
| German conservation workers inspect an urban garden for insects. Photograph: Sean Gallup/Getty Images |
Why are insects in decline,
and can we do anything about it?
What is the sixth mass extinction?
Many scientists think the current worldwide annihilation of wildlife is the beginning of a huge loss of species on Earth. It has happened five times in the last 4bn years, as a result of meteorite impacts, long ice ages and huge volcanic eruptions. But this one is the result not of natural causes, but of humanity’s actions. How bad is it? Extremely. By some measures, the biodiversity crisis is even deeper than that of climate change. Since the dawn of civilisation, humanity has caused the loss of 83% of all wild mammals. In the last 50 years alone, the populations of all mammals, birds, reptiles and fish have fallen by an average of 60%. How about insects? The new global review says it’s even worse for bugs, with the proportion of insect species declining being double that for vertebrates. The insect decline is at least a century old, but seems to have accelerated in recent decades. Does that matter? Yes. There are more than a million species of insect, compared with just 5,400 mammals, and they are the cornerstone of all terrestrial ecosystems. Without them, you get what scientists call a “bottom-up trophic cascade”, in which the knock-on effects of the insect collapse surge up through the food chain, wiping out higher animals. And without healthy ecosystems, there is no clean air and water. Why are we only really noticing the insect collapse now? The lack of bugs on car windscreens after a drive in the country, compared with a few decades ago, is real. But hard scientific data requires careful and long-term research, and relatively little has been done. Insects are small and often hard to identify, and they are certainly much less charismatic than elephants or eagles. Worse, just when we need more information, researchers say entomology courses are being cut. What can be done? Ultimately the size of the human population and how much land it uses for the food, energy and other goods it consumes determine how much wildlife is lost. Protecting wild spaces is important, as is reducing the impact of industrial, chemical-based farming. Fighting climate change is also vital, particularly for the many insect species in the tropics. So demanding political action, eating fewer intensively farmed meat and dairy products, and flying less could all help. |
In the tropics, where industrial agriculture is often not yet present, the rising temperatures due to climate change are thought to be a significant factor in the decline. The species there have adapted to very stable conditions and have little ability to change, as seen in Puerto Rico.
Sánchez-Bayo said the unusually strong language used in the review was not alarmist. “We wanted to really wake people up” and the reviewers and editor agreed, he said. “When you consider 80% of biomass of insects has disappeared in 25-30 years, it is a big concern.”
Other scientists agree that it is becoming clear that insect losses are now a serious global problem. “The evidence all points in the same direction,” said Prof Dave Goulson at the University of Sussex in the UK. “It should be of huge concern to all of us, for insects are at the heart of every food web, they pollinate the large majority of plant species, keep the soil healthy, recycle nutrients, control pests, and much more. Love them or loathe them, we humans cannot survive without insects.”
Matt Shardlow, at the conservation charity Buglife, said: “It is gravely sobering to see this collation of evidence that demonstrates the pitiful state of the world’s insect populations. It is increasingly obvious that the planet’s ecology is breaking and there is a need for an intense and global effort to halt and reverse these dreadful trends.” In his opinion, the review slightly overemphasises the role of pesticides and underplays global warming, though other unstudied factors such as light pollution might prove to be significant.
Prof Paul Ehrlich, at Stanford Universityin the US, has seen insects vanish first-hand, through his work on checkerspot butterflies on Stanford’s Jasper Ridge reserve. He first studied them in 1960 but they had all gone by 2000, largely due to climate change.
Ehrlich praised the review, saying: “It is extraordinary to have gone through all those studies and analysed them as well as they have.” He said the particularly large declines in aquatic insects were striking. “But they don’t mention that it is human overpopulation and overconsumption that is driving all the things [eradicating insects], including climate change,” he said.
Sánchez-Bayo said he had recently witnessed an insect crash himself. A recent family holiday involved a 400-mile (700km) drive across rural Australia, but he had not once had to clean the windscreen, he said. “Years ago you had to do this constantly.”
 |
| Volunteers look for the wormwood moonshiner beetle in Suffolk, UK. Photograph: Sean Smith/The Guardian |
- Why are insects in decline, and can we do anything about it?
- What is biodiversity and why does it matter to us?
- Worldwide decline of the entomofauna: A review of its drivers
- Earth's sixth mass extinction event under way, scientists warn
- Humanity has wiped out 60% of animal populations since 1970, report finds
- Humans just 0.01% of all life but have destroyed 83% of wild mammals – study
- Asymmetric boundary shifts of tropical montane Lepidoptera over four decades of climate warming
- Paul Ehrlich: 'Collapse of civilisation is a near certainty within decades'
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