Insect population decline will mean trouble for humans, too
by Sydney Cromwell
When you’re scratching a mosquito bite or shooing away flies, having fewer insects around might sound wonderful.
But insects are the foundations of ecosystems and agriculture around the world, and their loss would mean irreparable damage in our daily lives. So, many entomologists are raising the alarm over the signs of potential declines in insect populations — especially those oh-so-important pollinators — and the human behaviors that are driving this loss.
DEALING IN UNKNOWNS
When trying to study changes in insect populations, researchers are hindered by one big problem: We don’t know as much about bugs as we need to.
“We know almost nothing,” said Kendra Abbott, entomologist and museums research and outreach coordinator at the University of Alabama.
Kendra and her husband, John Abbott, who is a fellow entomologist and UA’s chief museum curator and director of research and collections, estimate there are more than 30 million species of insects in the world. Only about 1.7 million have been observed and described by scientists, they said.
“If we have 29 million species that we still have to identify, how can we know about what their population was?” Kendra Abbott said. “… We have such a long way to go with figuring out what we actually have on earth.”
Anthony Abbate, a research entomologist at Auburn University’s Bee Lab, said the situation is similar for native bees. About 350 bee species are known to live in Alabama, but some areas of the state haven’t been studied and little is known about these bees’ behaviors, he said.
“There’s kind of a high level of uncertainty concerning the native bee population in the United States,” Abbate said.
In light of these areas of incomplete knowledge, researchers tend to use insect biomass (the total number of insects found in a given area) as a surrogate for overall population. If entomologists return to the same area year after year but catch fewer insects, it’s likely that the local population is declining.
A 2017 study out of Germany used biomass collection at nature reserves over 27 years and found a 75% drop in flying insect populations, making headlines across the world and drawing the spotlight on the possibility of an “insect apocalypse.” Another German study published in 2019 found a 67% decrease in insect biomass over a decade, with the greatest population impacts happening near agricultural land.
Long-term studies of population decline are challenging to complete, Kendra Abbott said. These studies have to find consistent funding and staffing for years and deal with the possibility of development or other changes to the land where they’re monitoring populations.
“Generally there’s not funding for those types of studies,” Kendra Abbott said, particularly in tropical regions that have the most insect biodiversity.
Abbate said entomologists can also rely on museum specimens and records as a means of finding out where certain species have historically been found, and how frequently. They can then see if those same species can be captured in the same locations with similar frequency, to look for signs of population change.
Cornell University did such a study of its museum specimens of local bees in 2013 and found declines in the populations of 49 species out of 187.
It’s easier to get firm data for honeybees, Abbate said, since backyard and commercial beekeepers manage and keep close tabs on their colonies.
The Bee Informed Partnership surveys beekeepers about colony deaths every year, and the loss rate has hovered around 40% for several years. The 2020-2021 survey recorded an average 45.5% loss rate, the second highest rate in the survey’s history.
“That’s a big number. That’s pretty alarming to me,” Abbate said.
Population declines aren’t uniform around the world, or even between species of insects. A worldwide study published in 2020 showed that land-based insect species had declined by almost 1% per year, while freshwater species had actually become more abundant. Some entomologists have urged caution in taking a localized study, like the much-publicized German one from 2017, and generalizing its results to the rest of the world, where ecosystems and human land use can look quite different.
Kendra Abbott said she knows of entomologists in places like Mozambique and Puerto Rico, for example, who are seeing increases in local insect volume. A study on insect populations in the United States had decidedly mixed results in 2020, with some populations increasing, others decreasing and still others showing little change. Another research team’s results, published this spring, showed that population declines may actually be more pronounced in the tropics than in the rest of the world.
While the picture is incomplete and complicated, Kendra Abbott said there is, by and large, consensus among entomologists: “I would say if you ask any entomologist, they would say — in general, globally, they would agree that the abundance of insects is on the decline.”
That includes Abbate and the researchers at the Bee Lab.
“It’s definitely an issue that we’re seeing, and more so recently. We’ve been seeing declines in a lot of different pollinator species,” Abbate said. “… There’s good evidence that both commercially managed and wild pollinators are in decline.”
The Abbotts have seen signs of decline at their own home, as well. When they moved to Alabama in 2016, the couple bought a forested property, in part for the insect life. Since then, however, surrounding properties have been clear-cut and sprayed with pesticides, making the Abbotts’ home an “island” of woodland.
“The insect activity plummeted,” John Abbott said. “… There’s a very big difference between what I see now when I look in my black light every night than when we moved here.”
The Abbotts say insect decline can also be seen by casual observers. When she was growing up in Wisconsin, Kendra Abbott said her city had to use snow plows to clear away piles of short-lived mayflies, which die after a single day of adulthood. Now there aren’t large enough swarms to need those plows.
And people who have been driving for decades may remember a time when their cars’ windshields and grills needed constant cleaning due to insect “splats,” John Abbott said, but not anymore.
“I don’t think there’s any insect splats on our windshield. I don’t remember the last time I saw one,” he said. “… While it might be great that you don’t have to do that now, in certain areas, it’s certainly an indication that something’s changing,”
HARM TO BUGS, HARM TO US
If you ask why insects are disappearing, John Abbott puts it pretty bluntly: “We know exactly why there’s a decline, and that is there’s too many of us. … We’re trying to feed everybody, we’re trying to house everybody.”
Many of the choices that define modern human life are making it much harder for insects to survive: habitat destruction to make room for new development or agriculture, herbicide and insecticide use, air and water pollution and wildfire suppression, to name a few. John Abbott and other entomologists have called it “death by a thousand cuts.”
“All those modifications have really dramatic effects, and it’s catching up to us,” he said.
Kendra Abbott said habitat destruction is one of the most significant dangers to insects, whether it’s paving over a field to build a parking lot or replacing diverse ecosystems with “monocultures” of a single plant species, like grass lawns or lumber trees.
Former forests and prairies are now interrupted by roads, farmland, neighborhoods and businesses, not only reducing the available habitat but also making it more difficult for insects to reach the resources they need, Abbate said.
“The landscape is so fractured,” he said.
Habitat destruction is especially hard on those insects that rely on specific plants, such as the luna moth and sweet gum trees or the monarch butterfly and milkweed, Kendra Abbott said.
If their sources of food or shelter are destroyed through clear-cutting, herbicides, construction or pollution, some species won’t be able to move far enough or fast enough to find a new home. Instead, many of those local populations will simply die out.
“If we spray 200 acres with herbicides so that only loblolly pines can be grown, then suddenly we only have species that can live on loblolly pines,” Kendra Abbott said.
The Sarracenia spiketail dragonfly, a species that John Abbott described for the first time in 2011, is a perfect example of this, he says. The dragonfly relies on boggy habitats full of pitcher plants to thrive, and it has been found in only a few locations in Texas and Louisiana.
By suppressing wildfires, humans have allowed trees to encroach on those bogs and slowly dry them up, John Abbott said, reducing this dragonfly’s available habitat. Some of these areas are also popular with people off-roading in trucks and ATVs, further destroying the ecosystem. He said sometimes populations of dragonflies, salamanders and other creatures take a couple of years to rebound from the damage.
The endangered rusty-patched bumblebee, Abbate said, nests on the ground in a close congregation with other bees. If you pave a road through that area, “all those bees have been knocked out in one fell swoop,” he said.
Viruses, fungi and parasites like the varroa mite have wreaked additional havoc on honeybees and wild bee species, Abbate said.
“There’s definitely a whole slew of stressors that are creating or contributing to the decline that we’re seeing in bee species,” he said.
Insects are also victims of the temperature and weather changes caused by climate change, John Abbott said. Individual plant species and entire habitats are dying out or slowly shifting northward in response to rising temperatures, and weather patterns like floods, droughts, heat waves, wildfires and storms are getting more intense.
“Everybody talks about climate change and global warming, and I think insects are just another canary [in the coal mine]. And I think it’s going to be a pretty catastrophic canary. The planet cannot survive in its current form without insects,” John Abbott said.
The warming planet could be a temporary advantage to some insects. Last summer, Alabama had huge spikes in the numbers of crop pest insects due to heat and dry conditions, according to the Alabama Insect Pest Monitoring Report. Some more adaptable insects may also fill the ecological niches left behind by the disappearance of more vulnerable species.
However, the symptoms of climate change will continue to grow more severe if left unchecked, and the stress on worldwide insect populations will match that pace.
“All of these thousand cuts come back to: There’s too many people on the planet,” John Abbott said.
He said freshwater insects like stoneflies and mayflies are highly susceptible to damage from human actions like water pollution. So are native bees, butterflies and beetles, Abbate said.
The U.S. Fish and Wildlife Service currently includes more than 100 insect and arachnid species on its endangered species list. The rusty-patched bumblebee was added to the list in 2017, and the American bumblebee has completely disappeared from eight states and is under assessment for designation as an endangered species.
Since we only know a fraction of the insect life on the planet, Kendra Abbott said, the full scope of population decline can’t be understood.
“We’re losing species that we never knew we had,” she said.
A dramatic decline in insect populations would be an ecological catastrophe, starting with the plant species they pollinate and the creatures like birds and lizards that feed on insects, but the effects would inevitably ripple upward in the food chain. Research is already showing that bird population numbers are falling, too.
People would also feel the ripple effects far beyond splat-free windshields. More than a third of the world’s food crops depend fully or partially on insect and animal pollination, as do some other crops like cotton, tobacco and rubber plants. Without pollinators, fruits and vegetables could become less abundant and more expensive.
Aside from pollination, species like wasps and ladybugs are the predators of certain crop-damaging pest insects, and detritivores like earthworms and woodlice aerate and put nutrients into the soil.
“Not a lot of people know how insects are woven into our daily lives,” Kendra Abbott said.
Insects provide around $34 billion worth of pollination to U.S. agriculture every year. Worldwide, Kendra Abbott estimated the annual value of insect pollination, pest control, soil aeration and other services is closer to $500 billion. Without insects, people will either lose the benefit of those services or have to find — and pay for — ways to replace them.
“We’re literally boiling ourselves in a pot, and we’re not paying attention,” John Abbott said.
DROPS IN THE BUCKET
The backyard is a simple starting place for the protection of local insect populations, including planting a variety of native species and avoiding pesticide use.
“You need two main things, and it’s providing them food and providing them shelter,” Abbate said.
A little neglect can be healthy, too. In the summer, letting your yard grow longer will help bugs thrive. In the winter, dead plants and leaf litter become shelter for ground-dwelling native bees and other species.
“We hate mowing our lawn, and you know what? Not mowing is awesome for bugs,” Kendra Abbott said.
Buying produce when it’s in season and locally grown can also reduce the impact of agriculture on insects.
Abbate said some farmers have trouble getting enough honeybees from local keepers to pollinate their crops. He encourages farmers to plant strips of wildflowers at the edge of pollinator-dependent crops, as a “magnet” for the pollinators they need.
“You may not have to rely on honeybees as much if you’re pulling in native pollinators to your crops,” Abbate said.
However, all of these steps are drops in the bucket in comparison to the problem, John Abbott said. Preventing insect population decline is going to require large-scale changes in industrial agriculture, land development, pollution regulation and climate change response, he said.
“There’s a lot of evidence to suggest that, unfortunately, individual actions are going to do very little. It has to be policy, and it has to be at a large scale, to really effect any change,” John Abbott said.