Bat die-offs in the U.S. led to increased use of insecticides, which in turn led to greater infant mortality, according to a “seminal” study published Thursday that shows the effects of biodiversity loss on human beings.
Eyal Frank, an environmental economist at the University of Chicago, authored the study, which was published by Science, a leading peer-reviewed journal.
Bats can eat thousands of insects per night and act as a natural pest control for farmers, so when a fungal disease began killing off bat populations in the U.S. after being introduced in 2006, farmers in affected counties used more insecticides, Frank found. Those same counties saw more infant deaths, which Frank linked to increased use of insecticide that is harmful to human health, especially for babies and fetuses.
The study was greeted by an outpouring of praise from unaffiliated scientists for its methodology and the important takeaways it offers.
“[Frank] uses simple statistical methods to the most cutting-edge techniques, and the takeaway is the same,” Eli Fenichel, an environmental economist at Yale University, told The New York Times. “Fungal disease killed bats, bats stopped eating enough insects, farmers applied more pesticide to maximize profit and keep food plentiful and cheap, the extra pesticide use led to more babies dying. It is a sobering result.”
Carmen Messerlian, an environmental epidemiologist at Harvard University, told the Times the study “seminal” and “groundbreaking.”
The study shows the need for a broader understanding of human health that includes consideration of entire ecosystems, said Roel Vermeulen, an environmental epidemiologist at Utrecht University in the Netherlands. “It emphasizes the need to move from a human-centric health impact analysis, which only considers the direct effects of pollution on human health, to a planetary health impact assessment,” he told New Scientist.
Reporter Benji Jones echoed that sentiment in Vox, calling Frank’s findings “astonishing” and writing that such studies could help us fight chemical pollution by corporations.
“When the link between human and environmental health is overlooked, industries enabled by short-sighted policies can destroy wildlife habitats without a full understanding of what we lose in the process,” Jones said. “This is precisely why studies like this are so critical: They reveal, in terms most people can relate to, how the ongoing destruction of biodiversity affects us all.”
Frank, who said he started the work after stumbling on an article about bat population loss while procrastinating, happened upon an excellent natural experiment. The spread of white-nose syndrome, the fungal disease, was well tracked on a county-by-county level, leaving him with high-quality data that is hard to find for researchers who study the intersection of human and animal life.
The benefits of biodiversity on humans, and the drawbacks to its loss, are normally very difficult to quantify.
“That’s just quite rare—to get good, empirical, grounded estimates of how much value the species is providing,” Charles Taylor, an environmental economist at Harvard Kennedy School, told The Guardian. “Putting actual numbers to it in a credible way is tough.”
Taylor himself is the author of a somewhat similar study that showed that pesticide use and infant mortality rose during years in which cicadas appeared; the insects do so at 13-17 year intervals.
David Rosner, a historian based at Columbia University, said the new bat study joins a large body of evidence dating back to the 1960s that links pesticide use with negative human health outcomes. “We’re dumping these synthetic materials into our environment, not knowing anything about what their impacts are going to be,” he said. “It’s not surprising—it’s just kind of shocking that we discover it every year.”
Frank’s claim about the cause of increased infant mortality should be taken with some caution, said Vermeulen, the Dutch researcher. He said the loss of agricultural income caused by bat die-offs could be connected to the increased deaths in complex ways.
The exact causal mechanism isn’t known, Frank told media outlets, but the data shows the rise of infant mortality didn’t come from food contamination by insecticides—rather, it’s more likely it came via the water supply or contact with the chemicals.
Frank’s other research extends beyond pesticide use. He and another researcher recently estimated that hundreds of thousands of human beings have died in India due to the collapse of the country’s vulture population, as rotting meat increased the spread of diseases such as rabies.
Frank is not the first to study the impacts of white-nose syndrome on humans. Other studies have shown a reduction in land rents in counties hit by the bat plague and documented the billions of dollars that farmers have lost as their natural pest control disappeared.
The syndrome attacks bats while they hibernate. It was first identified in New York in 2006 and has since spread to much of North America. It’s believed to have been brought over from Europe. It doesn’t affect all bat species, but it’s killed more than 90% of three key species, and bats also face a myriad of other threats, including habitat loss, climate change, and the dangerous churn of wind turbines.
Frank’s bracing study should be a call to arms, experts said.
“This study estimates just a few of the consequences we suffer from the disappearance of bats, and they are just one of the species we’re losing,” Felicia Keesing, a biologist at Bard College, told The Washington Post. “These results should motivate everyone, not just farmers and parents, to clamor for the protection and restoration of biodiversity.”
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