In 2017, a team of German entomologists published a paper in PLOS ONE with a finding so large that several reviewers initially suspected methodological error. Over twenty-seven years of standardized trapping across sixty-three protected nature reserves, total flying insect biomass had declined seventy-five percent. Not species count. Not rare specimens. The total mass of every flying insect captured by identical traps in identical locations, measured in grams. Three-quarters of it was simply gone.

The Krefeld study, as it is now known, was a seismic event in ecology. It documented collapse inside legally protected areas where habitat destruction alone could not explain the decline. It forced the discipline and eventually the public to confront what longtime field naturalists had been describing for decades — the “windshield phenomenon,” the observation that summer drives no longer produce splatters of insects on car windshields the way they did a generation ago. What had been treated as nostalgia turned out to be a data point. The insects were gone.

01 /The Numbers Since Krefeld

The 2017 Krefeld findings have been extended, complicated, and broadly corroborated by nearly a decade of follow-on research. The picture is uneven — declines vary by region, taxon, and habitat — but the overall direction is unambiguous.

A 2019 review in Biological Conservation synthesized the available data and concluded that over forty percent of insect species are declining and a third are endangered — with insect extinction running roughly eight times faster than that of mammals, birds, or reptiles. A 2025 study by Keith Sockman at the University of North Carolina, published in Ecology, documented a 72.4% decline in montane insects across twenty years in remote high-altitude North American sites, associated directly with rising summer temperatures. The significance of Sockman’s finding is that it documents collapse in the kind of remote ecosystem previously assumed to be climate refugia. If mountain systems are losing insects this fast, there are no refugia.

A 2025 synthesis in Biological Conservation by Fang and colleagues framed the current consensus: insect population decline is predominantly driven by anthropogenic activities — habitat degradation, agricultural intensification, pesticide use — compounded by climate change through extreme weather events and shifting temperature regimes. The drivers interact. Climate change exacerbates the effects of habitat loss. Pesticide exposure weakens insect stress tolerance to climate shocks. Monocultures eliminate the refugia that would otherwise allow populations to persist through bad seasons. The result is not a single decline curve but multiple overlapping pressure vectors hitting the same populations at the same time.

02 /A Necessary Caveat

The science has one important internal dispute worth naming. A 2020 meta-analysis by Roel van Klink and colleagues, published in Science, found that terrestrial insect declines were real but slower than the Krefeld figures suggested, and that freshwater insects were actually increasing in some regions following water quality improvements. That finding was legitimate science; it was also quickly weaponized by agrochemical industry communications to argue the “insect apocalypse” narrative was overblown.

The scientific community has since broadly converged on a synthesis that incorporates both findings. Decline is real and severe, but spatially uneven. Temperate agricultural regions show the steepest losses. Tropical systems are poorly sampled and may show different patterns. Freshwater insects in some industrialized regions have recovered from twentieth-century pollution lows but remain below historical baselines and are now under new pressures from agricultural runoff and warming water. The honest description is that the “insect apocalypse” framing is broadly correct where the evidence is strongest, and that the evidence is strongest exactly where human food production depends on insects.

03 /What Insects Actually Do

The reason this matters enough to belong in a series about compounding crises is that insects are not one ecosystem service among many. They are the load-bearing layer of terrestrial ecology, and their functions cascade through the systems humans depend on in ways that most economic accounting never captures.

Pollination. Roughly seventy-five percent of leading global food crops depend to some degree on animal pollination. Not all of these would fail completely without insect pollinators — wind-pollinated staples like wheat and rice would not — but almost every fruit, vegetable, nut, oilseed, and stimulant crop in the human diet relies on insect pollinators. Coffee. Cocoa. Almonds. Apples. Stone fruit. Tomatoes. Squash. Most legumes. The diversity of the human diet collapses without them. Managed honeybees are a partial substitute for some crops but not for most, because honeybees are generalists and many crop plants have co-evolved with specific native pollinator species that are more efficient. Honeybee colonies are also themselves in decline — colony collapse disorder, Varroa mites, pesticide exposure, monoculture-induced nutritional stress.

Decomposition. Insects are the primary recyclers of organic matter on land. Dung beetles, carrion feeders, wood-boring beetles, termites, and the vast community of soil-dwelling insects convert dead organic material into the nutrients that plants can absorb. When these populations collapse, nutrient cycling slows. Soil fertility declines. Synthetic fertilizer substitutes exist but require energy-intensive industrial production that the fiscal and political order described in earlier parts of this series may not be able to sustain at current scales through a climate transition.

Food web support. Insects are the base of most terrestrial food webs. Bird populations in industrialized countries are collapsing in direct correlation with insect declines — European farmland birds have lost over half their abundance since 1980. Freshwater fish depend on aquatic insect stages. Amphibians depend on insects almost entirely. The downstream effects of insect collapse are biodiversity cascades that compound the original loss.

Pest control. Predatory and parasitic insects — ladybugs, parasitic wasps, ground beetles, lacewings — suppress the insect populations humans actually consider pests. Their loss forces increased pesticide use, which further damages the predators, which further forces pesticide escalation. This is a feedback loop in which industrial agriculture becomes progressively more dependent on chemical inputs to substitute for ecosystem services it is destroying.

04 /The Adaptation Scenario’s Hidden Premise

Here is where insect collapse compounds with the rest of this series. Every IPCC adaptation scenario, every climate-smart agriculture proposal, every food security projection, every humanitarian plan for climate-displaced populations, quietly assumes a functioning ecological substrate that is disappearing. The models assume pollinators will be there. They assume soil decomposer communities will continue to function. They assume pest control services will scale with changing climate zones. These assumptions are not tested in the scenarios because they are not usually visible as assumptions. They are the invisible floor the scenarios are built on.

The adaptation strategies that depend on this floor include most of the ones being actively planned. Moving crop zones poleward as climates warm requires pollinators that can follow or that already exist in the new zones. Many specialized pollinators cannot move fast enough or require specific vegetation that the crops do not bring with them. Shifting to drought-resistant crop varieties assumes those varieties remain pollinator-accessible. Agroforestry and regenerative agriculture explicitly depend on ecological community recovery, which insect collapse forecloses. Urban agriculture depends on pollinator access to city green spaces that are themselves contracting.

For humanitarian climate work specifically, the food security implications should already be visible in the data. Central American coffee production, which is heavily pollinator-dependent, has been declining for a decade under the combined pressure of warming, rust fungus, and pollinator loss. That decline feeds migration pressure. The people whose cases move through the Edward J. Schwartz Federal Building in downtown San Diego are, among many other things, the downstream consequence of agricultural systems whose ecological foundations are being eroded. Insect collapse, climate change, and the deportation pipeline are not separate stories; they are nodes in the same causal network.

05 /Why This Is the Hardest Part to Fix

The financial crisis of Part 01 is mechanically bad but operates on a short timeline and has conceivable policy responses. The imperial crisis of Part 02 is structurally severe but has historical precedent and diplomatic off-ramps. The climate crisis of Part 04 — still to come in this series — is civilizational in scope but within the reach of political mobilization if the window is captured.

Insect collapse is harder than any of these because it operates on biological timelines that do not correspond to political ones, and because the drivers are structurally entangled with the global food system. You cannot negotiate a ceasefire with neonicotinoids. You cannot monetize new biodiversity. You cannot rebuild pollinator populations on the ten-year horizon that political and financial crises operate on; even with immediate intervention, recovery requires decades, and in many cases requires habitat restoration at landscape scales that the fiscal capacity we are losing is needed to fund.

The policy tools that would slow it are known. Ban or severely restrict neonicotinoid and related systemic pesticides. Reduce monoculture acreage in favor of polyculture, hedgerows, and field margins. Restore wetlands. Reduce nitrogen deposition. Protect dark sky from light pollution that disrupts nocturnal insect populations. Fund IPBES and national pollinator protection plans. These are technically straightforward. They are politically opposed by the agrochemical industry and the agricultural commodity system built around high-input monoculture. In the United States specifically, the political coalition that would be needed to push through pollinator-protective regulation is the same coalition being fractured by the imperial and financial crises this series is tracing.

There is a version of the compounding argument that is easy to dismiss as catastrophism. Insect collapse makes it harder to dismiss, because the trajectory is documented, the timescales are not negotiable, and the downstream consequences for food systems and human populations are direct rather than speculative. The silent summer is not a metaphor. It is a measurement. And it is happening at the moment when the capacity to respond is being consumed by other crises that are themselves products of the same system that produced this one.

The next part of this series turns to the crisis this one implicates directly: the climate emergency itself, and the structural gap between the adaptation finance the world needs and what it is actually receiving. The UNEP 2024 Adaptation Gap Report puts the shortfall at ten to eighteen times current flows. Low-income countries pay more in debt service than they receive in climate finance. The fiscal capacity needed to adapt is exactly the capacity the financial and imperial crises are consuming. That is the engine of the compounding.