There have long been signs of such a decline. Studies have also shown that populations of European butterflies have halved since 1990, honeybee colonies have fallen by 59 percent in North American since World War II, and populations of British moths have dropped by 30 percent per decade. But most of these surveys focused on particular groups, whereas Hallmann’s group looked at the entire spectrum of flying insects. “It confirms the widespread, windscreen phenomenon,” he says. “Any truck driver in the developed world will tell you that they used to squash a lot of insects on the windscreen. Now the windscreens stay clean.”
“The study makes visible what otherwise has been an invisible decline in insect abundance,” says Michelle Trautwein, from the California Academy of Sciences. “Our mistreatment of the planet has been recognizably bad for elephants and coral reefs, but it seems likely that it has also been just as bad for flies, moths, beetles.”
This is, to put it mildly, a huge problem.
Insects are the lynchpins of many ecosystems. Around 60 percent of birds rely on them for food. Around 80 percent of wild plants depend on them for pollination. If they disappear, ecosystems everywhere will collapse. But also, insects are the most diverse and numerous group of animals on the planet. If they’re in trouble, we’re all in trouble.
There’s a debate about whether the Earth is in the middle of a sixth extinction—an exceptionally severe period of biological annihilation of the kind that has only happened five times before. One of the talking points in this debate is that, as Peter Brannen recently wrote, “when mass extinctions hit, they don’t just take out big charismatic megafauna, like elephants ... They take out hardy and ubiquitous organisms as well—things like clams and plants and insects.”
But remember that the German study only looked at one particular region. And it raises a question: If insects have disappeared by such a large degree, wouldn’t other species that depend on them be in much worse shape? Wouldn’t Germany’s flowers, birds, spiders, and reptiles also be plummeting? “We see great declines of insectivorous species—but not to this extent in most cases,” de Kroon acknowledges. “Some species could switch food sources, but we don’t really know what’s going on. We do know that we see declines in even common species, like blackbirds, starlings, and sparrows.”
Another unanswered question: Are all groups declining equally? “It would be interesting to see the list of species they collected, as Malaise traps are very good at collecting certain species and poor at collecting others, like dragonflies,” says Jessica Ware, from Rutgers University. “If insect [groups] vary in their response to climate change, temperature, habitat change, or other factors,” that could change the implications of the study’s stark percentages. (Hallmann notes that identifying the thousands of individuals in a single trap, let alone all 1,503, would mean months of work for a team of specialists. That’s why they focused on total weight.)