Dr. Francisco Sanchez-Bayo spent years working through 73 scientific studies from across the globe, searching for a pattern in the data on insect populations. What he found was not a pattern. It was a trend moving in a single direction. In 2019, he and co-author Dr. Kris Wyckhuys published their review in the journal Biological Conservation, and the number they presented stopped the scientific community: more than 40 percent of insect species are threatened with extinction. The rate of extinction, they found, is eight times faster than that of mammals, birds, and reptiles.
Insects comprise approximately two-thirds of all terrestrial species on Earth. They pollinate 75 percent of the world’s food crops. They are a food source for 60 percent of birds. They decompose organic matter, aerate soil, control pest populations, and form the base of food chains that reach from the ground to the top of the canopy. When Sanchez-Bayo described what losing them would mean, he did not reach for euphemism. “In about 100 years from now,” he said, “practically all the insects will be gone from the earth.”
The Number That Germany Proved First
The scientific debate about global insect decline began in earnest not with a model or a projection but with a jar. Specifically, tens of thousands of jars were collected by amateur entomologists in western Germany over more than three decades.
The Entomological Society Krefeld had been systematically trapping flying insects at 63 nature protection areas across Germany since 1989, using standardized malaise traps and preserving every specimen. The areas were protected. The methodology was consistent. The data accumulated for 27 years before Caspar Hallmann from Radboud University and colleagues subjected it to rigorous analysis. Their paper, published in PLOS ONE in October 2017, found that total flying insect biomass had declined by more than 76 percent over the course of the study, with mid-summer declines of up to 82 percent.
This was not a projection based on modeling. It was a direct measurement of weight. There was 76 percent less insect matter in these protected areas in 2016 than there had been in 1989. Protected areas. Places specifically designated to preserve biodiversity. The researchers tested weather, land use changes, and habitat characteristics as explanations. None of them accounted for the decline. The cause remains incompletely explained. The trend is not.
The German data was significant because it was long, consistent, and geographically diverse. It did not measure one species or one location. It measured the total mass of flying insects across dozens of sites over nearly three decades. When that number falls by 76 percent in protected nature areas, it is not a local anomaly. It is a signal.
What 75 Percent of Food Crops Depend On
The food chain consequence is not abstract. It is mathematical.
The Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services assessed pollinators, pollination, and food production in a two-year global study released in 2016, and found that between $235 billion and $577 billion worth of annual global food production relies on direct contributions by pollinators. Seventy-five percent of the world’s food crops depend at least in part on pollination by insects and other animals. That includes fruits, vegetables, seeds, nuts, and oils. It includes crops that provide vitamins and minerals that have no adequate substitute in caloric staples like wheat and rice, which are wind-pollinated and do not depend on insects directly.
What this means in practice: a world with drastically fewer insects is a world with drastically fewer options at the table. Not a world without food. But a world with far less variety, far lower nutritional density in the available diet, and far higher prices for the crops that remain because the free pollination service becomes expensive the moment it must be replaced. Chinese farmers in Sichuan Province have been hand-pollinating apple and pear trees with paintbrushes for years, following the local collapse of wild bee populations due to pesticide use. The task that billions of bees performed for free, in minutes, across vast areas, now requires human labor applied flower by flower.
The eastern population of the monarch butterfly has declined by approximately 80 percent in recent decades, according to population monitoring data. Some bumblebee species have declined in relative abundance by up to 96 percent in North America. These are not edge species, rare specialists that occupy narrow ecological niches. The monarch and the bumblebee are generalists. Their collapse is the point.
The Cascade Nobody Mapped
The food chain consequence of insect decline operates at multiple levels simultaneously, and the full scope of the cascade has not been adequately mapped. This is partly a data problem and partly a complexity problem.
Birds are the most immediately visible tier. Sixty percent of birds depend on insects as a food source at some point in their life cycle, including many that also eat seeds and berries. The decline in insectivorous bird populations across Europe and North America has tracked insect decline data closely. UK farmland bird populations fell by 56 percent between 1970 and 2015, according to government monitoring data. Swifts, swallows, flycatchers, and nightjars, birds defined by their dependence on flying insects, have declined across the continent. Their disappearance is not merely an aesthetic loss. Birds control insect pest populations, disperse seeds, and cycle nutrients in ways that sustain the plant communities that insects themselves depend on.
Below the birds, the consequences extend further and faster. Ground beetles, parasitic wasps, and predatory flies that control agricultural pests are themselves insects. The decline of beneficial insect predators is one reason pesticide use tends to escalate rather than decrease over time: remove the natural controllers, and the pests return at higher densities, requiring more intervention, which removes more of the natural controllers in a cycle that is difficult to interrupt.
Soil decomposition is the least visible consequence and possibly the most consequential. Dung beetles, burying beetles, and the countless smaller decomposers that break down organic matter and return nutrients to soil perform a service that the agricultural system has no substitute for. The same soil degradation that researchers tracking climate migration identify as a driver of displacement begins, in part, with the collapse of the invertebrate communities that maintain soil structure and fertility.
Why the Data Is Contested and Why That Does Not Make It Better
The 40 percent extinction figure from the Sanchez-Bayo and Wyckhuys study was challenged by multiple researchers in 2019, and those challenges deserve honest treatment.
The critics argued that the study searched the scientific literature using search terms related to “decline,” which biased the results toward papers documenting decreases and excluded papers documenting stability or recovery. At least seven peer-reviewed responses raised methodological concerns. The estimates across major global assessments, including those from IPBES, range from 10 to 40 percent of species at risk, not a single confirmed number.
The German biomass study, widely regarded as the strongest available data, is also geographically limited. It measured insects in 63 sites in western Germany. As of 2021, nearly all studies on regional insect population trends came from Europe and the United States, which account for less than 20 percent of insect species worldwide. Data from Africa, Asia, and South America are too sparse for comparable long-term analysis.
These limitations are real. They are also not a reason for comfort. The available data from the regions with the best monitoring shows a decline. The areas without monitoring are not being monitored precisely because they lack the research infrastructure and funding that the problem demands. Absence of evidence from most of the world is not evidence of absence of decline.
The same resource allocation gap that leaves Africa receiving under 3 percent of global clean energy investment despite hosting 60 percent of the world’s best solar resources also characterizes insect monitoring: the places with the most biodiversity have the least capacity to track what is happening to it.
What Is Killing Them
University of Sydney research by Dr. Sanchez-Bayo identified habitat loss through intensive agriculture as the primary driver, followed by agro-chemical pollutants, invasive species, and climate change.
The habitat loss mechanism is the most straightforward. Insects evolved in relationship with specific plant communities. Intensive agriculture replaces those communities with monocultures. A field of wheat or maize supports a fraction of the insect diversity that a mixed meadow or hedgerow supports. As intensively farmed land has expanded globally, the complex vegetative structure that most insect communities require has contracted. The insects that cannot adapt to the new landscape decline.
Neonicotinoid pesticides are the most studied of the chemical drivers. These systemic insecticides are absorbed by plants and expressed in pollen and nectar, which means that bees and other pollinators are exposed not through direct application but through normal foraging behavior. Sub-lethal effects on navigation, memory, and reproductive capacity have been documented in controlled studies. The European Union banned the outdoor use of three neonicotinoids in 2018. The United States has not imposed equivalent restrictions.
Climate change adds a timing dimension that compounds the other pressures. Many insects have evolved to emerge at specific times of year that synchronize with plant flowering or prey availability. As temperatures shift, these timing relationships break down. A bee that emerges three weeks earlier than a flower it depends on finds nothing to eat. The phenological mismatch that results is not fatal to a single individual. Repeated across enough species and enough years, it restructures ecosystems.
The Cascade Has Already Started
The swallows that once filled European summer skies in thousands are now counted in hundreds in many locations. Barn swallows across North America have declined by an estimated 30 percent since the 1960s. The nightjar, whose entire diet is flying insects, has become rare across habitats where it was once common. These birds did not disappear because of hunting or habitat destruction targeted at birds. They disappeared because the insects they depended on became scarce.
This is what a cascade looks like from the outside. Not a sudden collapse, but a progressive thinning that starts at the base and works upward through the food web in ways that are slow enough to miss year by year and shocking enough to be unmistakable across decades. The 76 percent biomass decline in German protected areas did not happen overnight. It happened over 27 years in the background, while the fields around those protected areas were managed as they had always been managed, and the assumption was that the insects were simply where they had always been.
The pace at which scientific discoveries are revealing consequences nobody anticipated suggests that the full downstream effects of insect decline on human health, food security, and ecosystem stability have not yet been fully characterized. The food chain consequence is not one that scientists say nobody is prepared for, because the data is uncertain. It is one nobody is prepared for because the scale of the response it requires has not been seriously contemplated by the institutions responsible for agricultural policy, land use regulation, or chemical safety assessment.
Dr. Sanchez-Bayo’s review found that 40 percent of insect species face extinction. Several researchers challenged the methodology. The German biomass data found that 76 percent of flying insect weight had already disappeared from protected areas in 27 years. Nobody challenged those jars. They were just jars. They held insects. Every year, for 27 years, there were fewer insects in them. The cascade does not wait for the methodology debate to resolve.
