A Downward Spiral

Evidence is growing that insects are in decline, but each of us can take steps to help. Our future depends on it.

Laura Tangley
Conservation
Jun 01, 2020

Comprising some three-quarters of all known animal species, the world’s estimated 3 to 30 million different kinds of insects display a dizzying diversity of sizes, shapes and colors. (Not shown to scale. For insect identifications and credits, see below.)

MOST PEOPLE ARE FAMILIAR with the sad story of North America’s monarch butterfly, whose populations have plummeted in the past few decades. Hardest hit are monarchs that breed west of the Rocky Mountains and winter on the coast of California, which have declined to less than 1 percent of their historic numbers. Not so well known: “Monarchs are far from the only California butterflies going downhill,” says Art Shapiro, professor of evolution and ecology at the University of California–Davis. “There are several species that are even worse off.”

He should know. Since 1972—for nearly half a century—Shapiro has been surveying butterflies once every two weeks from spring through fall along a transect in north-central California that stretches from sea level to the High Sierra. It is the longest-running butterfly monitoring project on the continent.

For the first two decades of this ambitious effort, Shapiro focused on annual fluctuations in the insects’ numbers in response to weather and other variables—“what scientists call noise,” he says. But beginning in the late 1990s, he became aware of a troubling long-term trend: Butterfly numbers were declining at nearly all of his 10 survey sites.

The exceptions were a handful of high-elevation locations. According to University of Nevada–Reno insect ecologist Matt Forister, a former graduate student of Shapiro’s who still analyzes much of the project data, “we looked at these mountain sites as refuges where butterflies could escape the pesticides and habitat loss that dominated the lowlands.” But all that changed during a four-year drought that began in 2011. “Even species at the highest elevations suffered,” Forister says, “and so far, they have not recovered.” At the lowland sites, meanwhile, nearly three-quarters of 70 butterfly species are still declining.

To Shapiro, the most surprising losses are of formerly widespread and abundant species. He cites the common sootywing, a shiny black butterfly with white specks that “once was indeed so common I could walk out of my office and pick larvae off weeds growing in cracks in the sidewalk,” he recalls. Today, there is just one population at a single site along the transect. Two other species, the large marble and the field crescent, have become “regionally extinct,” Shapiro says. “They’re just gone.”

Butterflies are “just gone” from many other places as well. A recent paper published in PLOS One reports that butterfly abundance in Ohio has declined by 33 percent during the past two decades. In the United Kingdom, a countrywide monitoring effort launched in the 1970s shows that 52 percent of butterfly species have declined in abundance, and the ranges of 47 percent have contracted. Scientists have recorded similar drops in both Sweden and Belgium.

“Monarch butterfly emerging from chrysalis

Monarch Butterfly (Danaus plexippus). The best known and most beloved of North American butterflies, the monarch migrates up to 4,000 miles round-trip each year, and its large winter gatherings are among the greatest natural spectacles on Earth. In the 1990s, hundreds of millions of butterflies made these epic journeys, but their numbers have dropped dramatically, with 80 percent fewer monarchs wintering in Mexico, and California’s winter population down by 99 percent.

The “windshield phenomenon”

Beyond butterflies—by far the best known of all insects—how are other six-legged species faring? It’s hard to say. Of an estimated 3 to 30 million insect species on the planet, only 1 million have been identified by scientists. For those that have, “we have virtually no baseline data and very few long-term population studies,” says Shapiro. Still, he and many other scientists have for years reported an alarming absence of these animals in places where they once were abundant.

“We’ve dubbed it ‘the windshield phenomenon,’” says Scott Black, executive director of the Xerces Society for Invertebrate Conservation. Decades ago, he explains, “a short drive down any road in the Midwest or on the Great Plains would yield hundreds of dead bugs splattered across the front of your car. But drive across the entire state of North Dakota, Nebraska or Iowa today, and your car will be practically spotless when you get to the other side.”

Many nonscientists have noticed a change as well: the diminishment of a vibrant insect ensemble that once enriched our lives—from scores of fireflies blinking on a warm summer night to swarms of moths spiraling around streetlights to clouds of colorful butterflies probing blooms for nectar in our backyard gardens. Ask almost anyone, and they will say that these natural spectacles are nowhere near as grand as they were just a decade or two ago.

But “human memories vary, and as scientists, we cannot rely on anecdotes to understand long-term wildlife trends,” admits Black. During the past few years, however, a growing number of scientific journals and institutions have published peer-reviewed papers and reports on the status of insects—and so far, they are confirming some of Black’s and his colleagues’ worst fears.

Among the most worrisome are reports about bumble bees—better known than most insects because they are critical pollinators of many plants, including crops. During the past two decades, scientists have discovered that four once-common and widespread North American bumble bee species—the western, rusty patched, yellow-banded and American bumble bee—have vanished from large parts of their ranges. A fifth, Franklin’s bumble bee, already may be extinct. A report published in 2015 by the Xerces Society and Bumblebee Specialist Group of the International Union for Conservation of Nature (IUCN) concluded that 28 percent of the continent’s 47 bumble bee species “face some level of extinction risk.” Similarly, Europe’s “red list” of imperiled species classifies just over 23 percent of its 68 bumble bee species as threatened.

Dispatches from other branches of the insect family tree tell similar tales—from declining moths in Scotland to drops in the abundance of tiger beetles, stoneflies and mayflies in the United States to decreases in beetles, moths and caddisflies in the Netherlands. Published in 2019 in Biological Conservation, a review of 73 insect-decline papers stated that the animals are disappearing so fast that more than 40 percent of the world’s insect species may be threatened with extinction in the next few decades.

Rusty Patched Bumble Bee (Bombus affinis). Distinguished from other Bombus species by a rusty spot on its back, the rusty patched bumble bee was once common in more than two dozen Eastern and Midwestern states. In recent years, however, it has vanished from nearly 90 percent of its range. An important pollinator of native wildflowers as well as cranberries, apples, plums and other crops, the species was listed as endangered in 2017.

Insect apocalypse?

One paper, published three years ago in PLOS One, attracted more attention than any other—and propelled the problem of insect declines into the public consciousness. Based on an analysis of 27 years of insect-trapping data in 63 protected areas across Germany, British, Dutch and German researchers discovered a stunning 76 percent decline in the total weight, or biomass, of hundreds of different species of flying insects—from butterflies, moths and bees to beetles, hoverflies, lacewings and katydids. Samples collected during the middle of summer, the height of the insect season, dropped by more than 80 percent.

The report made news worldwide, with headlines that warned of a coming “insect apocalypse” or “insect Armageddon.” Such sensationalism spurred a backlash from a number of entomologists, who do not believe scientists have enough long-term data on enough kinds of insects—particularly in the tropics, where most insects reside—to say that the group as a whole is declining.

“Little things that run the world”

Insect conservationists agree that more data are needed, but argue that we know enough to sound the alarm. “Every long-term study published to date has concluded that insects are declining in abundance, diversity and biomass,” Black says. In addition, new studies from the tropics are beginning to yield similar findings as those from the temperate zone. In one paper, published this year in Scientific Reports, Forister and several colleagues discovered what he calls “a shocking decline in more than 20 genera of moths” during 22 years in a protected Costa Rican rain forest.

Even if insects overall are declining less than such studies suggest, experts say delaying action to conserve them is too risky. In a speech he gave three decades ago at the National Zoological Park in Washington, D.C., renowned Harvard University entomologist E.O. Wilson famously called insects and other invertebrates the “little things that run the world.” The most-abundant animals on the planet, insects pollinate plants, aerate and fertilize soil and decompose dung as well as carcasses. In the United States alone, four services they provide—pollination, pest control, dung burial and wildlife nutrition—are worth at least $70 billion annually. “If human beings disappeared tomorrow,” Wilson warned, “the world would go on with little change. But if invertebrates were to disappear, I doubt that the human species could last more than a few months.”

The same goes for the rest of Earth’s animal species. Insects form the basis of food webs that “feed everything from fish on up to grizzly bears,” Black says. Birds, in particular, depend on them. According to University of Delaware entomologist Doug Tallamy, 96 percent of terrestrial birds rear their young on insects, even species that can survive on seeds and berries other times of the year.

And birds need a lot of insects: many thousands of them to rear just a single clutch of hatchlings, for example. On a global scale, Tallamy points to a recent report published in The Science of Nature estimating that, every year, the world’s insectivorous birds together consume approximately 400 to 500 million tons of insects.

No-regret solutions

The major drivers of insect declines—habitat loss, pesticides, pollution, invasive species and climate change—also are harming other species, including humans. Combating them, therefore, would provide wide-ranging benefits. To guide policymakers who want to take action, more than 70 scientists published in Nature Ecology and Evolution this January a “roadmap for insect conservation and recovery.” Its dozens of short- to long-term “no-regret solutions” range from increasing plant diversity in agricultural landscapes to reducing light, noise and water pollution. “We already know that many of these solutions work,” says Black. He cites an experiment in California’s Central Valley finding that hedgerows of native plants within monocultures of tomatoes or other crops boost pollinator diversity.

According to Tallamy, the beauty of insect conservation is that these animals are resilient and—because more than 70 percent of this country’s land is privately owned—“every individual can help restore our native insect fauna.” He recommends three steps you can take at home: stop spraying pesticides (used more per acre by homeowners than by farmers, he says), turn off unnecessary lights (which attract and kill insects when they exhaust themselves in pointless circling) and, perhaps most important, “landscape your yard with the native plants that nurture insects” rather than popular exotics such as ginkgo, crape myrtle and wisteria (all from Asia) that most native insects cannot eat.

“The good news is that nothing is inevitable about insect decline,” Tallamy says. “Each of us can help bring insects back by collaborating on a collective preserve built out of our own private yards”—a concept he calls the “homegrown national park” in his new book, Nature’s Best Hope.

Forister, too, imparts a hopeful message. Even in places where they’ve declined, he says, “insects are still clinging to the edges. If we open the door for them a little, they can bounce back.” But he adds a warning: “This is true now, but we don’t know if it will be true 10 to 20 years from now.”

Learn how to landscape your property for insects and other native wildlife at nwf.org/garden.

INSECT IDENTIFICATION AND CREDITS

1 Meleager’s blue butterfly (Polyommatus daphnis) DIRK FUNHOFF (NPL) 2 Common housefly (Musca domestica) MARKO MASTERL (NPL) 3 Damselfly nymph (Zygoptera sp.) NIALL BENVIE (NPL) 4 Lichen moth (Hypoprepia sp.) CLAY BOLT 5 Straight-snouted weevil (Arrhenodes sp.) PIOTR NASKRECKI (NPL) 6 Stag beetle (Lucanus cervus) MARC PIHET (NPL) 7 Halloween pennant dragonfly (Celithemis eponina) CLAY BOLT 8 Metallic green bee (Agapostemon splendens) CLAY BOLT 9 Potter/mason wasp (Eumenes sp.) PIERRE ESCOUBAS (NPL) 10 Hooded mantis (Choeradodis sp.) GIL WIZEN (NPL) 11 Stink bug (Chlorocoris sp.) JOAO P. BURINI (NPL) 12 Common flightless katydid (Isophya savignyi) GIL WIZEN (NPL) 13 Carpenter bee (Xylocopa myops) JORIS VAN ALPHEN (NPL) 14 Small red-eyed damselfly (Erythromma viridulum) DIRK FUNHOFF (NPL) 15 Nocturnal parasitic Ophionine wasp (Ophioninae sp.) CLAY BOLT 16 Stink bug nymph (Pentatomidae sp.) CLAY BOLT 17 Rove beetle (Plochinocerus sp.) JAVIER AZNAR (NPL) 18 Large forest pyrgomorph (grasshopper) (Desmoptera truncatipennis) LILY KUMPE (NPL) 19 Crimson-speckled flunkey (Utetheisa pulchella) GIL WIZEN (NPL) 20 Soldier grasshopper nymph (Chromacris speciosa) JP LAWRENCE (NPL) 21 Leaf-footed bug (Coreidae sp.) ANDREW SNYDER (NPL) 22 Field cricket (Gryllus campestris) PAUL VAN HOOF (NPL) 23 Velvet ant (Hoplomutilla sp.) GIL WIZEN (NPL) 24 Leaf mimicking katydid (Typophyllum sp.) CLAY BOLT 25 Silk moth (Automeris sp.) JAVIER AZNAR (NPL) 26 Polka-dot wasp moth (Syntomeida epilais) CLAY BOLT 27 Green horsefly (Chlorotabanus crepuscularis) CLAY BOLT 28 Stick insect (Phasmidasp.) JORIS VAN ALPHEN (NPL) 29 Velvet ant (Dasymutilla quadriguttata) JP LAWRENCE (NPL) 30 Six-spotted tiger beetle (Cicindela sexguttata) CLAY BOLT 31 Carpenter ant (Camponotus sp.) DAVID WONG (NPL) 32 Slant-faced grasshopper (Mermiria sp.) CLAY BOLT 33 Giant Amazon dung beetle (Coprophanaeus lancifer) ANDREW SNYDER (NPL) 34 Caterpillar (Limacodidae sp.) JAVIER AZNAR (NPL) 35 Green-veined white butterfly (Pieris napi) DIRK FUNHOFF (NPL) 36 Eastern scissor grinder cicada (Neotibicen winnemanna) CLAY BOLT 37 Transverse ladybird (Coccinella transversalis) LILY KUMPE (NPL) 38 Long-faced grasshopper (Truxalis grandis) GIL WIZEN (NPL) 39 Walking stick (Orxines sp.) CLAY BOLT 40 Eastern Hercules beetle (Dynastes tityus) CLAY BOLT 41 Lanternfly nymph (Fulgoridae sp.) CLAY BOLT 42 Reddish-brown stag beetle (Lucanus capreolus) CLAY BOLT 43 Ground beetle larva (Dicaelus sp.) CLAY BOLT 44 Flatid planthopper (Poekilloptera phalaenoides) ANDREW SNYDER (NPL).