As many of Wilson’s colleagues soon realized, the significance of the theory extended well beyond actual islands. Through logging and mining and generalized sprawl, the world was increasingly being cut up into “islands” of habitat. The smaller and more isolated these islands, be they patches of forest or tundra or grassland, the fewer species they would ultimately contain. Wilson had moved on to new research questions, and initially didn’t concern himself much with the implications of his own work. When the first surveys of deforestation in the Amazon appeared, though, he was, in his words, “tipped into active engagement.” In an article in Scientific American, in 1989, he combined data on deforestation with the predictions of his and MacArthur’s theory to estimate that as many as six thousand species a year were being consigned to oblivion. “That in turn is on the order of 10,000 times greater than the naturally occurring background extinction rate that existed prior to the appearance of human beings,” he wrote.

The same year that Wilson published his article in Scientific American, a group of insect fanciers installed what are known as malaise traps in several nature reserves in Germany. Malaise traps look like tents that have blown over on their sides, and they’re designed to capture virtually anything that flies into them. The group, the Krefeld Entomological Society, was interested in how insects were faring in different types of parks and protected areas. Every summer from then on, society members set out new traps, usually in different preserves. In 2013, they resampled some of the sites they’d originally sampled back in 1989. The contents of the traps were a fraction of what they’d been the first time around.

Over the next three summers, the group members resampled more sites. The results were similar. In 2017, with the help of some outside experts, they published a paper documenting a seventy-five-per-cent decline in “total flying insect biomass” in the areas surveyed. These areas were exactly the sort of habitat fragments that, according to Wilson’s theory, were destined to lose species. Nevertheless, the findings were shocking. In 2019, a second group of researchers published a more rigorous and extensive study, and its findings were even more dire. In the course of just the previous decade, grasslands in Germany had, on average, lost a third of their arthropod species and two-thirds of their arthropod biomass. (Terrestrial arthropods include spiders and centipedes in addition to insects.) In woodlands, the number of arthropod species had dropped by more than a third, and biomass by forty per cent. “This is frightening” is how one of the paper’s authors, Wolfgang Weisser, a biologist at the Technical University of Munich, put it.

In the years since, many more papers have appeared with comparable findings. Significant drops have been found in mayfly populations in the American Midwest, butterfly numbers in the Sierra Nevadas, and caterpillar diversity in northern Costa Rica. While many species appear to be doing just fine—for instance, the spotted lanternfly, an invasive species from Asia, which was first detected in Pennsylvania around 2014, and has since spread to at least ten other states, including New York—there is, as was noted in the introduction to a recent special issue of the Proceedings of the National Academy of Sciences devoted to the state of the insect world, “ample cause for concern.”

Dave Goulson, an entomologist at the University of Sussex, is one of the experts the Krefeld group contacted to help make sense of its data. Like Wilson, Goulson could be described as a naturalist turned post-naturalist; he decided to study insects because he found them enthralling, and now he studies why they’re in trouble.

“I have watched clouds of birdwing butterflies sipping minerals from the muddy banks of a river in Borneo, and thousands of fireflies flashing their luminous bottoms in synchrony at night in the swamps of Thailand,” he writes in “Silent Earth: Averting the Insect Apocalypse” (Vintage). “I have had enormous fun. But I have been haunted by the knowledge that these creatures are in decline.”

Goulson bemoans the fact that many people consider insects to be pests. He wants readers to appreciate just how amazing they really are, and sets off his chapters with profiles of six-legged creatures. Males of many species of earwigs have two penises; if disturbed during mating, they snap off the one they’re using and beat a quick escape. Female jewel wasps sting their prey—large cockroaches—to induce a zombielike trance. Then they chew off the tips of the roaches’ antennae, use the stumps to guide the stupefied creatures back to their burrows, and lay their eggs inside them. Aging termites of the species Neocapritermes taracua develop pouches around their abdomens that are filled with copper-rich proteins. If an intruder is gaining the upper hand—or leg—in a fight, the elderly termites, in effect, blow themselves up to protect the colony, a practice known as suicidal altruism. The proteins react with chemicals stored in their salivary glands to become highly toxic compounds.

Insects are, of course, also vital. They’re by far the largest class of animals on Earth, with roughly a million named species and probably four times that many awaiting identification. (Robert May, an Australian scientist who helped develop the field of theoretical ecology, once noted, “To a first approximation, all species are insects.”) They support most terrestrial food chains, serve as the planet’s chief pollinators, and act as crucial decomposers. Goulson quotes Wilson’s observation: “If all mankind were to disappear, the world would regenerate back to the rich state of equilibrium that existed 10,000 years ago. If insects were to vanish, the environment would collapse into chaos.”

Like insects themselves, the threats to them are numerous and diverse. First, there’s habitat loss. Since Wilson’s article in Scientific American appeared, in 1989, South America has lost at least another three hundred million acres of tropical forest, and Southeast Asia has experienced similar losses. In places like the U.S. and Britain, which were deforested generations ago, the hedgerows and weedy patches that once provided refuge for insects are disappearing, owing to ever more intense agricultural practices. From an insect’s perspective, Goulson points out, even fertilizer use constitutes a form of habitat destruction. Fertilizer leaching out of fields fosters the growth of certain plants over others, and it’s these others that many insects depend on.

Climate change, light pollution, and introduced species present further dangers. The Varroa destructor mite evolved to live on (and consume the body fat of) Asian honeybees, which are smaller than their European counterparts. When European honeybees were imported to East Asia, the mites jumped hosts, and when European bees were taken to new places the mites hitched a ride. Varroa mites carry diseases like deformed-wing virus, and they’ve had a devastating effect on European honeybees, probably causing the loss of hundreds of thousands of colonies. In the U.S. (and in many other countries), European honeybees are treated as tiny livestock. They’re carted around to pollinate crops like apples and almonds, and their health is carefully monitored. But what’s been the impact of imported parasites and pathogens on other bees, not to mention ants, beetles, crickets, dragonflies, moths, thrips, and wasps? “For 99.9 per cent of insect species, we know simply nothing,” Goulson laments.

Then, there are pesticides. Since the Fire Ant Wars, which were prominently featured in Rachel Carson’s “Silent Spring,” a great many have been taken off the market. New ones, however, have replaced them. Goulson is particularly concerned about a class of chemicals known as neonicotinoids. Neonics, as they’re often called, are, in some respects, even more toxic than Mirex and chlordane. They were first marketed in the nineteen-nineties; by 2010, more than three million pounds a year were being applied to crops in the U.S., and almost two hundred thousand pounds to crops in Great Britain. Neonics are water-soluble, which means they can leak into soils and ponds and potentially be taken up by other plants. There’s a good deal of controversy over the dangers they pose to non-target insects, especially bees; in 2018, the European Union found the evidence of harm compelling enough to ban three key neonics from outdoor use. (The chemicals continue to be applied in many European countries under “emergency authorizations.”) Meanwhile, in the rest of the world, including the U.S., their use continues apace. “Carson may have won a battle, but not the war,” Goulson observes.

In the last chapter of “Silent Earth,” Goulson offers dozens of actions we can take to “change our relationship with the small creatures that live all around us.” Some involve tending one’s own garden—for instance, trying “to reimagine ‘weeds’ such as dandelion as ‘wildflowers.’ ” Others are regional or national in scope: “plant streets and parks with flowering, native trees” or “introduce pesticide and fertilizer taxes.” The list is long enough that nearly everyone who wants to can find some recommendation to follow, but it’s heavily tilted toward reducing the use of pesticides, which, as “Silent Earth” makes clear, is just one of the many hazards insects are facing.

Wilson, who’s been called the “father of biodiversity,” has a bigger idea. In “Half-Earth: Our Planet’s Fight for Life” (2016), he argues that the only way to preserve the world’s insects—and, for that matter, everything else—is to set aside fifty per cent of it in “inviolable reserves.” He arrived at the figure, he explains, using the principles of island biogeography; on fifty per cent of the globe, he calculates, roughly eighty-five per cent of the planet’s species could be saved. The task of preserving—or, in many places, restoring—half the world’s habitat is, he acknowledges, daunting. The alternative, though, is to grow dandelions while the world burns: “The only hope for the species still living is a human effort commensurate with the magnitude of the problem.” ♦

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