Claims that insects will disappear within a century are absurd, but the reality isn’t reassuring either.
The drumbeats of doom began in late 2017, after a German study showed that the total mass of local flying insects had fallen by 80 percent in three decades. The alarms intensified after The New York Times Magazine published a masterful feature on the decline of insect life late last year. And panic truly set in this month when the researchers Francisco Sánchez-Bayo and Kris Wyckhuys, having reviewed dozens of studies, claimed that “insects as a whole will go down the path of extinction in a few decades.” The Guardian, in covering the duo’s review, wrote that “insects could vanish within a century”—a crisis that Sánchez-Bayo and Wyckhuys believe could lead to a “catastrophic collapse of nature’s ecosystems.”
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?
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 Warefrom 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.”