BY ED YONG
Claims that insects will disappear within a century are absurd, but the reality isn’t reassuring either.
In 1828, a teenager named Charles Darwin opened a letter to his cousin with “I am dying by inches, from not having anybody to talk to about insects.” Almost two centuries on, Darwin would probably be thrilled and horrified: People are abuzz about insects, but their discussions are flecked with words such as apocalypse and Armageddon.
I spoke with several entomologists about whether these claims are valid, and what I found was complicated. The data on insect declines are too patchy, unrepresentative, and piecemeal to justify some of the more hyperbolic alarms. At the same time, what little information we have tends to point in the same worrying direction. How, then, should we act on that imperfect knowledge? It’s a question that goes beyond the fate of insects: How do we preserve our rapidly changing world when the unknowns are vast and the cost of inaction is potentially high?
The sheer diversity of insects makes them, as a group, resilient—but also impossible to fully comprehend. There are more species of ladybugs than mammals, of ants than birds, of weevils than fish. There are probably more species of parasitic wasps than of any other group of animal. In total, about 1 million insect species have been described, and untold millions await discovery. And having learned of a creature’s existence is very different from actually knowing it: Most of the identified species are still mysterious in their habits, their proclivities, and—crucially for this discussion—their numbers.
Few researchers have kept running tallies on insect populations, aside from a smattering of species that are charismatic (monarch butterflies), commercially important (domesticated honeybees), or medically relevant (some mosquitoes). Society still has a lingering aversion toward creepy crawlies, and entomological research has long been underfunded. Where funds exist, they’ve been disproportionately channeled toward ways of controlling agricultural pests. The basic business of documenting insect diversity has been comparatively neglected, a situation made worse by the decline of taxonomists—species-spotting scientists who, ironically, have undergone their own mass extinction.
When scientists have collected long-term data on insects, they’ve usually done so in a piecemeal way. The 2017 German study, for example, collated data from traps that had been laid in different parts of the country over time, rather than from concerted attempts to systematically sample the same sites. Haphazard though such studies might be, many of them point in the same dispiriting direction. In their review, Sánchez-Bayo and Wyckhuys found 73 studies showing insect declines.
But that’s what they went looking for! They searched a database using the keywords insect and decline, and so wouldn’t have considered research showing stability or increases. The studies they found aren’t representative either: Most were done in Europe and North America, and the majority of insects live in the tropics. This spotty geographical spread makes it hard to know if insects are disappearing from some areas but recovering or surging in others. And without “good baselines for population sizes,” says Jessica Ware from Rutgers University, “when we see declines, it’s hard to know if this is something that happens all the time.”
For those reasons, it’s hard to take the widely quoted numbers from Sánchez-Bayo and Wyckhuys’s review as gospel. They say that 41 percent of insect species are declining and that global numbers are falling by 2.5 percent a year, but “they’re trying to quantify things that we really can’t quantify at this point,” says Michelle Trautwein from the California Academy of Sciences. “I understand the desire to put numbers to these things to facilitate the conversation, but I would say all of those are built on mountains of unknown facts.”
Still, “our approach shouldn’t be to downplay these findings to console ourselves,” Trautwein adds. “I don’t see real danger in overstating the possible severity of insect decline, but there is real danger in underestimating how bad things really are. These studies aren’t perfect, but we’d be wise to heed this warning now instead of waiting for cleaner studies.”
After all, the factors that are probably killing off insects in Europe and North America, such as the transformation of wild spaces into agricultural land, are global problems. “I don’t see how those drivers would have a different outcome in a different area, whether we know the fauna there well or not,” says Jennifer Zaspel from the Milwaukee Public Museum.
Insects, though diverse, are also particularly vulnerable to such changes because many of them are so specialized, says May Berenbaum from the University of Illinois at Urbana-Champaign. “There’s a fly that lives in the gills of a crab on one Caribbean island,” she says. “So what happens if the island goes, or the crab goes? That’s the kind of danger that insects face. Very few of them can opportunistically exploit a broad diversity of habitats and supplies.” (That said, Sánchez-Bayo and Wyckhuys concluded that several once-common generalist species are declining, too.)
The loss of even a small percent of insects might also be disproportionately consequential. They sit at the base of the food web; if they go down, so will many birds, bats, spiders, and other predators. They aerate soils, pollinate plants, and remove dung and cadavers; if they disappear, entire landscapes will change. Given these risks, “do we wait to have definitive evidence that species are disappearing before we do something?” Berenbaum asks.
Doing something is hard, though, because insect declines have so many factors, and most studies struggle to tease them apart. In their review, Sánchez-Bayo and Wyckhuys point the finger at habitat loss above all else, followed by pesticides and other pollutants, introduced species, and climate change, in that order. “If it was one thing, we’d know what to do,” says Moreau from Cornell. Instead, we are stuck trying to tend to 1 million smaller cuts.
Youngsteadt of North Carolina State is also confused by the sudden flux of interest, but it has meant a lot of invitations from community groups that want her to talk about the declines. She advises them to plant their gardens with native flowers, which promote a wider diversity of insects than neatly manicured lawns. Many people heed that advice to save beautiful species such as monarchs, “but are shocked by all the bugs that come over,” Moreau says. “They’ll see flies, bees, other caterpillars. They start appreciating the whole realm of insects out there. Going from ‘Ew!’ to ‘I’ve heard they’re in trouble; what can I do?’ is a good thing.”
She and others hope that this newfound attention will finally persuade funding agencies to support the kind of research that has been sorely lacking—systematic, long-term, widespread censuses of all the major insect groups. “Now more than ever, we should be trying to collect baseline data,” Ware says. “That would allow us to see patterns if there really are any, and make better predictions.” Zaspel would also love to see more support for natural-history museums: The specimens pinned within their drawers can provide irreplaceable information about historical populations, but digitizing that information is expensive and laborious.
“We should get serious about figuring out how bad the situation really is,” Trautwein says. “This should be a huge wake-up call, and we should get on the ball instead of quibbling.”