The collapse of insects

As a boy in the 1960s, David Wagner would run around his family’s Missouri farm with a glass jar clutched in his hand, scooping flickering fireflies out of the sky.

“We could fill it up and put it by our bedside at night,” says Wagner, now an entomologist.

That’s all gone, the family farm now paved over with new homes and manicured lawns. And Wagner’s beloved fireflies – like so many insects worldwide – have largely vanished in what scientists are calling the global Insect Apocalypse.

As human activities rapidly transform the planet, the global insect population is declining at an unprecedented rate of up to 2% per year. Amid deforestation, pesticide use, artificial light pollution and climate change, these critters are struggling — along with the crops, flowers and other animals that rely on them to survive.

“Insects are the food that make all the birds and make all the fish,” said Wagner, who works at the University of Connecticut. “They’re the fabric tethering together every freshwater and terrestrial ecosystem across the planet.”

The tree of life

It’s easy to think insects are doing OK. After all, they’re nearly everywhere — crawling through rainforest canopy, burrowing into soil, skimming freshwater ponds or, of course, flitting through the air.

On the biological “tree of life” — which classifies organisms to describe their evolutionary and genetic relationship to one another — insects fall under the branch, or phylum, called Arthropods, one of the 40 branches of the Animal Kingdom.

In terms of diversity, insects are unrivaled, representing two-thirds of the world’s more than 1.5 million documented animal species with millions more bugs likely still undiscovered, scientists say. By comparison, there are roughly 73,000 vertebrates, or animals with a backbone from humans to birds and fish — these represent less than 5% of the known Animal Kingdom, according to the International Union for Conservation of Nature (IUCN).

Their importance to the environment can’t be understated, scientists say. Insects are crucial to the food web, feeding birds, reptiles and mammals such as bats. For some animals, bugs are simply a treat. Plant-eating orangutans delight in slurping up termites from a teeming hill. Humans, too, see some 2,000 species of insects as food.

But insects are so much more than food. Farmers depend on these critters pollinating crops and churning soil to keep it healthy, among other activities.

• Insects pollinate more than 75% of global crops, a service valued at up to $577 billion per year, the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES) says.

• In the United States, insects perform services valued in 2006 at an estimated $57 billion per year, according to a study in the journal BioScience.

• Dung beetles alone are worth some $380 million per year to the U.S. cattle industry for their work breaking down manure and churning rangeland soil, the study found.

With fewer insects, “we’d have less food,” said ecologist Dave Goulson at the University of Sussex. “We’d see yields dropping of all of these crops.”

And in nature, about 80% of wild plants rely on insects for pollination. “If insects continue to decline,” Goulson said, “expect some pretty dire consequences for ecosystems generally — and for people.”

Diversity

Dividing the more than 1 million known insect species into commonly understood categories illustrates how insects significantly outnumber all other animals.

Bugs in decline

Describing a stroll through Costa Rica’s Area de Conservacion Guanacaste rainforest, evolutionary ecologist Daniel Janzen in 2019 wrote: “Gone are the spiderwebs that decades back entangled those leaves. Gone is the nighttime sparkle in the leaves reflected from thousands of lycosid spider eyes.”

The world has lost 5% to 10% of all insect species in the last 150 years — or between 250,000 and 500,000 species, according to a February 2020 study in the journal Biological Conservation. Those losses are continuing, though estimates vary due to patchy data as well as uncertainty over how many insects exist.

In the tropics, insects can be “extremely hard to identify, because there are vastly more species than (we) are used to,” Janzen, a University of Pennsylvania professor, told Reuters. “There are more species within 100 kilometres of my dwelling in a national park in northwestern Costa Rica than in all of Europe.”

Not knowing exactly what’s out there makes it harder to detect trouble. One April 2020 analysis in the journal Science suggested the planet is losing about 9% of its land-dwelling insect population each decade. Another January 2021 paper tried to paint a clearer picture by synthesizing more than 80 insect studies and found that insect abundance is declining around 1% to2% per year. For comparison, the human population is growing at slightly less than 1% per year.

“Even at the low end of 1% a year, after just 40 years you’re down more than one-third of species and one-third of individuals — a third of the entire tree of life lost,” said Wagner, who led the 2021 metastudy, published in the Proceedings of the National Academy of Sciences.  But the reality is likely worse. Wagner’s team offered an “incredibly conservative” loss estimate, he said, noting that many insect studies are conducted in protected areas such as nature reserves. Degraded farmland or cities would likely reveal far fewer insects.

A world of dangers

The demise of insects can’t be attributed to any single cause. Populations are facing simultaneous threats, from habitat loss and industrial farming to climate change. Nitrogen overloading from sewage and fertilizers has turned wetlands into dead zones; artificial light is flooding out nighttime skies; and the growth of urban areas has led to concrete sprawl.

“Until recently, loss of land was the single greatest driver” of the decline, Wagner said. “But climate change is becoming a far more severe and ominous threat by drying out parts of the planet that were chronically wet. And that is absolutely catastrophic for a lot of insects.”

The introduction of non-native plants, which can dominate new environments, has also hurt insects. Because many insects have evolved to feed on or fertilize a single plant species, the disruption of the plant world can have an outsized effect. For example, the Tegeticula moth species pollinates California’s famed Joshua trees, with the succulent providing the only food source for the moth’s offspring. If Joshua trees were to disappear, so too could the moth. And vice versa.

Winners and losers

While the situation is bleak for insects at large, a few species are thriving.

“It’s generally the pest insects that are thriving because they’re the ones that breed faster and are favored by human conditions, like all the waste we produce for them to lay their eggs in,” said Sussex’s Goulson.

Climate change is also giving some nuisance species a boost. Rising temperatures are driving major outbreaks of mountain pine bark beetles, which in two decades have decimated roughly 100,000 square miles (260,000 square kilometers) of North American forest. And with warmer, wetter weather, two disease-spreading mosquitoes Aedes aegypti and Aedes albopictus are expected to expand in Asia, North America and Europe, putting an additional 2.3 billion people at risk from dengue fever by 2080, a June 2019 Nature Microbiology study estimated.

Beyond pests, here are some more examples of other insect groups that are in trouble:

Bees (Order Hymenoptera)

These pollinators are in peril. Threatened bumblebees include 28% of North America’s species and 24% in Europe, according to the IUCN. North America’s rusty-patched bumblebee has seen its range shrink by 87% in the last 20 years.

U.S. honeybee colonies, which are trucked across the county to pollinate cucumbers, almonds and other commercial crops, have been declining steadily for decades, with about 2.7 million colonies now compared with some 6 million in 1947. The U.N. Food and Agricultural Organization has warned that the decline in bees threatens global food security.

Butterflies and moths (Order Lepidoptera)

Bees aren’t the only pollinators being hit. Many moth and butterfly populations are also struggling due to habitat loss as well as pesticides and herbicides. As of 2010, nearly a third of Europe’s native butterfly species were declining, and 81 of the continent’s 482 species were considered threatened or near threatened, according to the IUCN.

In the western United States, the number of individual butterflies has been steadily decreasing over the past four decades, at a rate of around 1.6% every year, according to a March 2021 study in the journal Science. The iconic Monarch butterfly is one of the species in trouble. Warmer autumn temperatures, an effect of climate change, may be interfering with the butterflies’ hibernation-like period known as diapause. So rather than slowing down ahead of winter, the insects are staying awake longer, expending more energy, and eventually starving to death, scientists say. In July, the migratory monarch was added to the IUCN’s global endangered species list.

Beetles (Order Coleoptera)

Tiger beetles, part of the ground beetle family, live in sandy coastal burrows. Being sensitive to change, they are good indicator species for environmental health. Today, around 15% of U.S. tiger beetle species and subspecies are in a state of decline or considered very rare. Conservation groups partially blame off-road vehicles for destroying the beetles’ larval burrows.

Fireflies, also known as lightning bugs, may soon blink out. Fourteen of 128 firefly species — which make up a family within the beetle order — are threatened in the U.S. and Canada, according to the conservation group Xerces Society. Urban light pollution, thought to be partially responsible, can confuse fireflies, which rely on their own nighttime bioluminescence to attract mates and repel predators.

Freshwater insects

According to IUCN data, 16% of assessed dragonfly and damselfly species are threatened, and around 10% are in decline.

While the April 2020 Science study noted a decline in insects on land, it found that freshwater insects are recovering at a rate of 11% per decade overall thanks partly to clean water legislation passed in Europe and the United States. But the situation is worsening in South Asia and Southeast Asia, where many wetland breeding grounds have been cleared for crops. Today, more than a quarter of the region’s dragonflies and damselflies are threatened.

Research bias

IUCN data from 2021 show that, of the roughly 1 million known insect species, the conservation status of only about 1% has been assessed. So while scientists are certain that insect abundance is dropping fast, they aren’t entirely sure which insects are most at risk.

Because the insect class is so vast, that 1% of insects assessed represents roughly the same number of species as the 100% of birds assessed, and twice the number of mammals assessed.

Backboned animals, particularly charismatic mammals, tend to attract more research funding than insects. A European research project looking at a vertebrate species, for example, receives nearly 500 times more funding on average than an invertebrate study.

Out of all insects assessed, one in five — or 2,270 in total — is considered threatened.

The graphic below breaks down the number of the assessed species by insect sub-groups, known as orders. Some groups have had no species assessments whatsoever and don’t feature in the graphic at all. Others may only have a very small number assessed and of those, all are threatened, such as stoneflies and mayflies.