Bats have a bad reputation, but they deserve better. The flying mammals are nature’s pest control, swooping over America’s farmland every night to feast on swarms of insects that would otherwise chew through crops.
But many of the country’s bat populations are on the decline, wiped out by a devastating fungus that attacks the insect eaters in their sleep.
Now, a new study suggests that decline in bats has come at a ghastly cost to human beings.
An analysis published Thursday in the journal Science suggests farmers have increased their use of pesticides on crops in response to the population collapse of bats, potentially leading to the deaths of more than 1,000 human infants through intoxication from the chemicals. Past research has linked exposure to pesticides with negative health outcomes, including childhood asthma and death.
The finding, though an indirect observation, is a potentially poignant demonstration of the benefits society derives from nature – and, in turn, of the deadly cost to humans when biodiversity is lost.
“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,” said Bard College biology professor Felicia Keesing, who was not involved in the study. “These results should motivate everyone, not just farmers and parents, to clamor for the protection and restoration of biodiversity.”
Around the world, nature – and by extension, people – are in trouble. Hundreds of thousands of plants and animals are at risk of vanishing forever due to habitat destruction, climate change and other human activities, an extinction crisis potentially on par with the asteroid that wiped out most dinosaurs. In response, nations have promised to protect roughly a third of land and oceans to maintain ecosystems essential to human society.
Over the past few years, researchers have revealed many of the hidden ways healthy ecosystems help people thrive. A surge in wolves in Wisconsin resulted in fewer cars colliding with deer, for instance, while a decline in amphibians in Central America led to an uptick in malaria cases.
AN ATTACK ON BATS
For bats, the trouble started about two decades ago, when biologists found a cave in Upstate New York littered with bat carcasses. Their noses were covered in white fuzz, as if each bat had done a line of cocaine. A fungus – one imported from Europe or Asia, perhaps on a hiker’s boot – was attacking the bats during their winter slumber.
The deadly disease was dubbed white-nose syndrome. It quickly spread across the country, reaching 40 states. The fungus doesn’t infect humans, but that doesn’t mean it is leaving them unscathed. While the damage to bats themselves is clear – the pathogen has wiped out more than 90% of some species – the broader effect of the loss of the voracious insectivores on the entire ecosystem was unclear.
To suss out that impact, Eyal Frank, an environmental economist at the University of Chicago, compared insecticide use and human infant mortality rates in U.S. counties where the fungus has been spotted to those where it has yet to be found.
Frank found that between 2006 and 2017, farmers increased their use of pesticides by about 31% in counties where bats were dropping dead due to disease.
Knowing that pest-killing compounds can spread through the air and water beyond farms and have negative health effects after they enter people’s bodies, he also analyzed infant mortality rates in each county and saw a nearly 8% spike in places where bats were hit by the disease. Frank tested to see if his results were somehow explained by other factors, including the opioid epidemic or unemployment, and saw no effects. “I kicked a lot of different tires.”
“Bats are a fantastic example of a species that we like to keep a distance from, but are really impactful in terms of the role they play in ecosystems.,” Frank said.
AN ‘EYE-POPPING’ EFFECT ON PEOPLE
Frederik Noack, an environmental economist at the University of British Columbia, found the findings credible and showed how technological solutions such as pesticides are often a poor substitute for the services that nature provides. The study estimated that white-nose syndrome cost farmers about $27 billion in total.
But he added that study still leaves unanswered questions for further research, including how babies are exposed to insecticides, where insect-eating bats are concentrated across the country and why the study found no effect on other health outcomes such as birth weight.
“Given the large effects, we should investigate the pathways through which pesticides affect birth outcomes. So far, it is unclear how people get exposed to pesticides,” said Noack, who co-wrote a policy analysis that accompanied Frank’s research.
Keesing, the Bard College biologist, noted the study didn’t directly measure changes in bat or insect populations and said she would like to see more field research.
“Without seeing the underlying data, I can’t evaluate the strength of the evidence supporting these linkages, but the impacts estimated here are eye-popping,” she said.
Other scientists are now racing to figure out a way to stop the spread of the fungus, deploying ultraviolet lights on cave walls and administering vaccines to bats themselves to snuff out the disease.
“It is not only the mega charismatic species that are warm and fuzzy and evoke a desire to hug and cuddle with them that provide value and benefit to us as people,” Frank said.
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