Bats are considered a natural pesticide, and farmers widely rely on them as an alternative to chemical pesticides to protect their crops from insects. But since 2006, many bat populations have collapsed in North American counties due to an invasive fungus found in the caves bats use during the day and winter that causes what is known as white-nose syndrome. A new study in Science It uses the sudden collapse of crops to investigate whether farmers resorted to chemical pesticides and whether this affected human health. The study concludes that farmers increased their use of pesticides, leading to the deaths of more than 1,000 children.
“Bats have gotten a bad reputation as something to be feared, especially after reports of a possible link to the origins of COVID-19,” says study author Eyal Frank, an adjunct professor at the Harris School of Public Policy. “But bats do add value to society in their role as natural pesticides, and this study shows that their decline may be harmful to humans.”
Frank compared the effect of bat die-offs on pesticide use in counties that experienced those bat population declines to counties that were likely not affected by the wildlife disease. He found that when bat populations declined, farmers increased their pesticide use by about 31 percent. Since pesticides have been linked to negative health impacts, Frank tested to see if increased pesticide use corresponded with an increase in infant mortality, a common marker for studying the health impacts of environmental pollution. Indeed, when farmers increased their pesticide use, the infant mortality rate increased by nearly 8 percent. This corresponds to 1,334 additional infant deaths. Or, for every 1 percent increase in pesticides, there was a 0.25 percent increase in the infant mortality rate.
The study also found that pesticides are not as good at preventing pests as bats. Crop quality likely declined, as farmers’ income from crop sales dropped by nearly 29 percent. Combining this loss of income with pesticide spending, farmers in communities that experienced mass bat die-offs lost $26.9 billion between 2006 and 2017. Adding to those losses the $12.4 billion in damages from child mortality, the total societal cost of mass bat die-offs in these communities rose to $39.6 billion.
“When bats are no longer there to do their job of controlling insects, the costs to society are very high, but the cost of conserving bat populations is likely lower,” Frank says. “More broadly, this study shows that wildlife adds value to society and we need to better understand that value so we can inform policies to protect them.”