Grams in the Mesh

The Jars of Krefeld

Mara: At five or six, Dave Goulson found stripy yellow-and-black caterpillars on weeds in his school playground. He put them in his empty lunchbox and took them home. In 2015, by then a researcher at the University of Sussex, he heard from the Krefeld Society, a group of German entomologists. As he later wrote in the Guardian, they'd been trapping flying insects on nature reserves since the late 1980s. Fifty-three kilos of insects, from decades of trapping. They sent him the data and asked for help getting it into a scientific journal.

Eli: That pile of insects is where the listener's question starts: what would happen if all the insects disappeared? Today's angle is a paradox of steep flying insect biomass losses alongside freshwater recoveries.

Mara: Dave Goulson had the trap data.

Eli: They were Malaise traps. It's basically a tent of fine mesh standing in a meadow. Flying insects hit the wall and get funnelled up into a collecting bottle. Krefeld volunteers ran the same standardized traps across 63 protected sites, from 1989 to 2016. Which is why the numbers bite. In 1989 the average trap caught about 1.6 kilos of insects between May and October. By 2014, it was about 300 grams.

Mara: Inside nature reserves. The land that was meant to be safe.

Eli: Over the 27 years, flying-insect biomass fell by roughly three-quarters. In midsummer, closer to 82 percent.

Mara: That's what Dave Goulson had in front of him. Whether a crash in protected land means insects everywhere are going is the open part, and Eli has the version where they're all gone.

The Thought Experiment

Eli: Once that analysis was out, Dave Goulson put it bluntly: 'If we lose the insects then everything is going to collapse.'

Mara: Everything is a big word for a scientist to use.

Eli: He meant it in sequence. Without pollination, he wrote later, wild flowers would not set seed, and most would eventually disappear. Then go the animals that eat insects, and the animals that eat those. That's trophic collapse: when the bottom floor of a food web goes, the floors above come down with it.

Mara: And the bottom floor is wide. In 2016, an alliance of British research institutions said over three-quarters of wild flowering plants in temperate regions need animals like insects to fully develop fruit and seed. Without those visits, that's pollination failure: the flower opens, nobody comes, no seed forms. And it reaches the farm. Researchers at Cambridge count coffee, rapeseed and most fruits among the crops that rely on pollinators.

Eli: So that's the coffee and the fruit bowl.

Mara: Then the eaters. Lynn Dicks, a Cambridge zoologist, lists 'birds, bats, some mammals, fish, reptiles and amphibians.' Hans de Kroon calls insects a main food source for most birds, mammals and amphibians. Take the insects away and those animals starve.

Eli: Plants have had a very long time to find workarounds, though.

Mara: Researchers in the Paris region tested what's happening right now. They grew field pansies from seeds collected in the same spots between 1992 and 2001, next to today's pansies. Today's had smaller flowers and about 20 percent less nectar, and pollinators visited them less.

Eli: So the pansies are already backing out of the deal, long before any insect is gone for good. What's emptying those protected reserves in the first place, the traps alone can't say.

Soils and Monocultures

Mara: Those pansies are a small warning for all the wild flowers that depend on insects. And the insects' work doesn't stop at flowers.

Eli: Much of it is underground, or face down in dung. Dicks says flies, beetles and wasps are 'predators and decomposers, controlling pests and cleaning up the place generally.' That cleaning is nutrient cycling: dung and dead things broken back down into plant food. Dung beetles bury droppings, which clears pastures and keeps grassland soil fertile. Ecologists once valued that burial at over 380 million dollars a year to American ranchers.

Mara: Which is the part nobody pictures when they picture insects.

Eli: And there's a human cost before any famine. Goulson notes that wind-pollinated crops like wheat, rice and maize could still supply the calories. But living on bread, rice and porridge would, in his words, 'quickly see us succumb to deficiencies of essential vitamins and minerals.' Nutritional analyses point the same way: vitamin and mineral gaps would show up long before the calories ran out.

Mara: Which brings Goulson back to the farm. 'Farmland has very little to offer for any wild creature,' he said in 2017. Big arable fields mean agricultural homogenization: a varied patchwork gives way to one crop to the horizon, and there's far less habitat for insects. Scientists add pesticides, monocultures like corn and soybeans, urbanization and outright habitat destruction to the list.

Eli: A list long enough to make blaming one thing hard.

Mara: Rodolfo Dirzo, a Stanford ecologist, suspects 'a multiplicity of factors,' with habitat destruction, fragmentation, urbanization and agricultural conversion leading.

Eli: So the suspects live on and around the farm. That sharpens what this story keeps circling: whether a collapse of flying insects means Earth is losing all its insects, or the real crisis lies somewhere else. Some serious people were about to answer with the bleakest word available, Mara.

The Apocalypse Narrative

Mara: One of them had come at it from the birds. In 2014, Hans de Kroon and his PhD student at Nijmegen had published a paper in Nature linking falling numbers of insect-eating songbirds, skylarks, barn swallows, yellow wagtails, to pesticides. The thought experiment's starving birds, showing up for real. But a link was missing. De Kroon: 'We already assumed there had to be fewer insects available as food for those birds, but we couldn't prove it. Until suddenly the Germans turned up on our doorstep.'

Eli: So Krefeld's traps held the proof they'd been missing.

Mara: Proof of the shortage, yes. The cause was harder. The reserves were small, and 94 percent of the trap sites were hemmed in by farm fields. Thomas Hörren, who works on the Krefeld surveys, reads that as pointing at farming, its chemicals above all.

Eli: Yet the drivers the team tested, from more arable land to warming, explained only about a fifth of the decline.

Mara: That's a lot of crash with no culprit. Most of the year-to-year swings, around 80 percent, stayed unexplained. Pesticides were among the suspects, he says, 'but we're ten years on now and we know there isn't a single cause.' So the crash was real, the birds felt it, and what caused it was still open.

Eli: Into that gap came the bleak version. In 2019, a review of reports from around the world estimated that about 40 percent of insect species were declining and could face extinction within decades.

Mara: Krefeld's alarm, scaled up to the whole planet.

Eli: Scaled up is exactly it. That's an insect apocalypse projection: decline rates measured in particular places, stretched into extinction across the planet. Dave Goulson's warning about everything collapsing sat neatly beside it.

Mara: Other reviewers cautioned that it shouldn't be used as evidence of global insect trends. So the sharper issue isn't whether Krefeld was real. It's whether anyone had measured enough of the world to say all insects were going.

A Complex Reality

Eli: The Krefeld archive Goulson examined held something narrower than that. It's regional biomass. It isn't a count of every insect species on Earth, and it never projected that they'd all disappear. Even Hans de Kroon's fear was about the trend continuing: he said it's hard to imagine what happens if another three-quarters of what's left is lost too. A world with no insects at all is a thought experiment. Nobody has watched it happen, so its consequences can only be estimated.

Mara: A regional alarm, then, not a planetary death count.

Eli: And when Roel van Klink's team pooled studies worldwide, the picture split. Land insects declined. Freshwater insects increased, possibly as rivers and lakes recovered from pollution. Even neighbouring sites showed opposite trends. That's taxonomic heterogeneity: different groups going down, holding steady or rising, all at once.

Mara: Ann Swengel, after 34 years watching butterflies, saw both: 'We've seen so much decline, including on many protected sites. But we've also observed some sites where butterflies are continuing to do well.'

Eli: So two readings stand. Dave Goulson and Francisco Sánchez-Bayo see a broad collapse across species and habitats. Van Klink and Swengel see a patchwork: steep losses in some settings, stability or gains in others.

Mara: And for van Klink and Swengel, the patchwork has winners. They note a handful of species increasing, all adaptable generalists moving into the spaces the declining ones left. Then there's where the counting happens. The long-term data come mostly from temperate Europe and North America. That's monitoring geographic bias: the surveys cluster in a few well-studied regions, and much of the world goes barely counted.

Eli: Van Klink's team found no clear trend elsewhere. The data there were too thin.

Mara: Rodolfo Dirzo said as much back in 2016: 'Unfortunately, information on invertebrates in general, including insects, is very limited, restricted to a few groups and a few localities.' What's documented is heavy loss.

Eli: That leaves the trajectory in the places where losses are measured: whether they're easing, holding, or still falling.

The Road Ahead

Mara: One measure comes off the front of cars. In November 2025, Buglife published its latest Bugs Matter results. It's a windscreen splat survey: motorists across the UK count the insects squashed on their number plates after journeys. Over five years, that count fell by 59 percent. Rosie Bleet, presenting the findings, added a caveat: 'These results are extremely concerning, particularly if insect splats serve as an accurate measure of insect populations.'

Eli: Organizers and Dave Goulson read it as the same loss the reserve traps measured.

Mara: And the German reserve work kept going. In March 2025, Thomas Hörren said there was no sign of recovery in recent years. On the contrary, the collapse of many populations was continuing. His group had also found dozens of pesticide ingredients from neighbouring farms reaching the core zones of nature reserves, with consequences, he said, for birds, plants and soils.

Eli: So the farmland that hems the reserves in is reaching inside them.

Mara: Which splits the listener's question in two: the imagined world, and the measured one.

Eli: The imagined one first: lose every insect. The science explainer site WhatIfLab adds two wrinkles. Insects don't do all the pollinating or all the decomposing, so the damage would be severe but uneven across ecosystems. And insect-eaters wouldn't fare alike. Some could switch to other prey. Specialists couldn't. That's dietary vulnerability: the narrower the menu, the harder the fall.

Mara: So: all insects gone is catastrophe. What's measured is deep, regional loss, worst around farmland.

Eli: And regional loss can be worked on. In the Dutch Ooijpolder, farmers and researchers planted hedgerows and flower borders. De Kroon: 'Here in the Ooijpolder we can see that when you make room for nature again, insect numbers bounce straight back.' That's the restoration rebound. Locals even told researchers, 'You say things are going so badly, but we think we are doing quite well here.' The Paris pansies showed plants drifting away from missing insects. This is the reverse: 'You can really get it back quite rapidly,' de Kroon says, 'but you have to help it a little bit.'

Mara: Dave Goulson saw a crash, and it's still being measured. Two things to watch. Whether new standardized trap networks in tropical forests and the Southern Hemisphere start publishing years of baseline data. And whether landscape experiments can finally pull apart pesticides, local climate shifts and habitat fragmentation as causes inside reserves.

Eli: Dig into Malaise trap.

Mara: And keep following science with us.

Eli: That's it for today. I'm Eli.

Mara: And I'm Mara. Thanks for listening, and until next time on Angle.