Where Have All the Insects Gone?
National Geographic Magazine India|May 2020
BUGS ARE DISAPPEARING AT ALARMING RATES. THAT COULD BE DISASTROUS FOR THE PLANET.
ELIZABETH KOLBERT

THE BUTTERFLIES JUST KEPT COMING—at first thousands, then tens or even hundreds of thousands. Their wings were brown on the underside and vivid orange above, so as they flew by, they looked like chips of sunshine. The sight was marvelous, awe-inspiring, and more than a little disconcerting.

I encountered the butterfly cloud—technically, an irruption of California tortoiseshells — on a bright blue summer day in the Sierra Nevada. Along with Matt Forister, a biologist from the University of Nevada, Reno, I was hiking Castle Peak, a knob-shaped mountain northwest of Lake Tahoe. Castle Peak’s butterflies are one of the world’s most closely watched insect populations: Every summer for nearly 45 years they’ve been censused on a biweekly basis. Most of the data were collected by Forister’s mentor, Art Shapiro, a passionate lepidopterist and professor at the University of California, Davis, who recorded the information on three-by-five cards.

After Forister and his team computerized the surveys and analyzed them, they found that Castle Peak’s butterflies have been in decline since 2011. We were discussing why this was the case when we neared the 9,100-foot summit and were enveloped in an orange haze.

“The idea that insects are suffering seems shocking to people, which I understand,” Forister said. He gestured at the butterflies streaming by: “Insects do this, so it does seem weird.”

It’s said that we live in the Anthropocene—an epoch defined by human impacts on the planet. Still, by many measures, it’s bugs that dominate the world. At any given moment, it’s been estimated, there are 10 quintillion insects flying, crawling, hovering, marching, burrowing, and swimming around. In terms of variety, the numbers are equally impressive: Something like 80 percent of all the different kinds of animals are insects. They maintain the world as we know it: Without insects to pollinate them, most flowering plants, from daisies to dogwoods, would die out.

If humans were to suddenly disappear, biologist Edward O. Wilson has famously observed, the Earth would “regenerate back to the rich state of equilibrium that existed 10,000 years ago.” But “if insects were to vanish, the environment would collapse into chaos.”

It is, therefore, shocking—and alarming—that in most places scientists have looked recently, they’ve found that insect numbers are falling. This is the case in agricultural areas and in wild places like Castle Peak. Quite probably, it’s also happening in your own backyard.

THE ENTOMOLOGICAL SOCIETY of Krefeld, Germany, on the Rhine River not far from the Dutch border, stores its collections in a former schoolhouse. Where kids used to fidget through class, the rooms now hold boxes filled with bottles, and the bottles, in turn, are filled with clumps of dead insects floating in ethanol. If there were a ground zero for the exploding concern about insect decline, the schoolhouse would be it.

“We don’t count the bottles, because the number changes every week,” Martin Sorg, the head curator of the collection, told me. He estimates that there are “several tens of thousands.”

In the late 1980s Sorg and his colleagues set out to find how insects were faring in different types of protected areas in Germany. To get a handle on this, they set up what are known as malaise traps, which look like tilted pup tents. The traps caught everything that flew into them, including flies, wasps, moths, bees, butterflies, and lacewings. Whatever a trap caught ended up in a bottle.

The collecting went on for more than 20 years, first in one spot, then another, in 63 protected areas, mostly in the state of North-Rhine- Westphalia, where Krefeld is located. In 2013 the entomologists returned to two sites that they’d first sampled back in 1989. The mass of trapped insects was just a fraction of what it had been 24 years earlier. They sampled those sites again in 2014 and set about resampling more than a dozen other sites. Wherever they collected, the results were similar.

To interpret the results, the society enlisted the help of other entomologists and statisticians, who painstakingly sifted through the data. Their analysis confirmed that from 1989 to 2016, flying insect biomass in protected areas in Germany had declined by a whopping 76 percent.

This finding, published in the scientific journal PLOS One, made headlines around the world. The Guardian warned of “ecological Armageddon,” the New York Times of “insect Armageddon.” The Frankfurter Allgemeine Zeitung declared that “we find ourselves in the middle of a nightmare.” According to the website Altmetric, which tracks how often published research is mentioned online, the study was the sixth most discussed scientific paper of 2017. The once-obscure Krefeld Entomological Society was deluged with scientific and media requests, and it remains so to this day. “There simply is no end,” Sorg said, sighing.

Since the Krefeld paper, entomologists all over the world have been poring over records and collections. Some scientists argue there’s a bias in the published papers; they say a study that shows dramatic changes is more likely to be printed than one that doesn’t. Still, the results have been sobering. Researchers working in a protected forest in New Hampshire found that the number of beetles there had fallen by more than 80 percent since the mid-1970s, while the bugs’ diversity—the number of different kinds— had dropped by nearly 40 percent.

A study of butterflies in the Netherlands found their numbers had declined by almost 85 percent since the end of the 19th century, while a study of mayflies in the upper Midwestern U.S. found their populations had dropped by more than half just since 2012. In Germany a second team of researchers confirmed the gist of the Krefeld results. They found that from 2008 to 2017, the number of insect species in the country’s grasslands and forests—sampled repeatedly in hundreds of sites in three widely spaced protected areas—had fallen by more than 30 percent.

“It is frightening,” said one of the researchers, Wolfgang Weisser, a professor at the Technical University of Munich. But it “fits the picture presented in a growing number of studies.”

PEOPLE MAY DELIGHT in butterflies and detest mosquitoes, but most insects we simply ignore. This says way more about creatures with two legs than it does about creatures with six.

Insects are far and away the most diverse creatures on the planet, so much so that scientists are still struggling to figure out how many different kinds there are. About a million insect species have been named, but it’s generally agreed that many more—by recent estimates some four million more—have yet to be discovered. Just one family of parasitoid wasps, the Ichneumonidae, sometimes called Darwin wasps, contains something like 100,000 species, greater than the number of all known species of fish, reptiles, mammals, amphibians, and birds combined. (The mere existence of the Ichneumonidae, Charles Darwin once argued to a friend, was enough to disprove the biblical theory of creation, as no “beneficent and omnipotent God” would have designed such a ghoulish, murderous parasite.) Other insect families are similarly big; there are, for example, perhaps 60,000 species of Curculionidae, commonly known as weevils.

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