Be very afraid of a plague without locusts

People rely on healthy ecosystems for everything from nutrient cycling to local weather, and the more species make up an ecosystem the more stable it is likely to be.

“Be afraid. Be very afraid,” says a character in The Fly, a film about a man who turns into an enormous insect. It captures the unease and disgust people often feel for the kingdom of cockroaches, zika-carrying mosquitoes and creepy-crawlies of all kinds.

However, ecologists increasingly see the insect world as something to be frightened for, not frightened of.

In the past two years scores of scientific studies have suggested that trillions of murmuring, droning, susurrating honeybees, butterflies, caddisflies, damselflies and beetles are dying off.

“If all mankind were to disappear,” wrote EO Wilson, the doyen of entomologists, “the world would regenerate … If insects were to vanish the environment would collapse into chaos.”

Most describe declines of 50 per cent and more over decades in different measures of insect health. The immediate reaction is consternation. Because insects enable plants to reproduce through pollination, and are food for other animals, a collapse in their numbers would be catastrophic. “The insect apocalypse is here,” trumpeted The New York Times last year.

But a second look leads to a different assessment. Rather than causing a panic, the studies should act as a timely warning and a reason to take precautions.

The movie poster for the original 1958 movie The Fly, which played on humans’ fear of creepy-crawlies.

That is because the worst fears are unproven. Only a handful of databases record the abundance of insects over a long time — and not enough to judge long-term population trends accurately. There are no studies at all of wild insect numbers in most of the world, including China, India, the Middle East, Australia and most of South America, South-East Asia and Africa. Reliable data are too scarce to declare a global emergency.

Moreover, where the evidence does show a collapse — in Europe and America — agricultural and rural ecosystems are holding up. Although insect-eating birds are disappearing from European farmlands, plants still grow, ­attract pollinators and reproduce. Farm yields remain high. As some insect species die out, others seem to move into the niches left, keeping ecosystems going, albeit with less biodiversity. It is hard to argue that insect decline is yet wreaking significant economic damage.

But there are complications. Agricultural productivity is not the only measure of environmental health. Animals have value, independent of any direct economic contribution they may make.

People rely on healthy ecosystems for everything from nutrient cycling to local weather, and the more species make up an ecosystem the more stable it is likely to be. The extinction of a few insect species among so many might not make a big difference. The loss of hundreds of thousands would.

And the scale of the observed decline raises doubts about how long ecosystems can remain resilient. An experiment in which researchers gradually plucked out insect pollinators from fields found plant diversity held up well until about 90 per cent of insects had been removed. Then it collapsed. In Krefeld, in western Germany, the mass of aerial insects declined by more than 75 per cent between 1989 and 2016. As one character in a novel by Ernest Hemi ngway says, bankruptcy came in two ways: “gradually, then suddenly”. Given the paucity of data, it is impossible to know how close Europe and America are to an ecosystem collapse. But it would be reckless to find out by actually triggering one.

Insects can be protected in two broad ways, dubbed sharing and sparing. Sharing means nudging farmers and consumers to adopt more organic habits, which do less damage to wildlife. That might have local benefits, but organic yields are often lower than intensive ones. With the world’s population rising, more land would go under the plough, reducing insect diversity further. So sparing is needed, too. This means going hell for leather with every high-yield technique you can think of, including insecticide-reducing genetically modified organisms, and then setting land aside for wildlife.

Insects are indicators of ecosystem health. Their decline is a warning to pay attention to it — before it really is too late.