Save the Bats, Save the World: A Grim Natural Experiment Links Wildlife Disease to Human Infant Mortality

The scourge of North American bats known as white-nose syndrome first appeared on the scene in 2006, traced to a single site, upstate New York’s Howe Cavern. The disease is caused by a fungus, Geomyces destructans, which results in the white fuzz for which it is named. Even among the sorts of invasive diseases that humans help ferry around the planet all the time, it is a bad scene — and a new study shows just how bad not just for the bats, but for the farmers and people around them as well.

WNS causes hibernating bats to wake up — something many species do anyway at a few points over the winter, but not all that often. The irritation from the fungus has some bats waking up every few days instead of every few weeks, and the electrolyte imbalance it causes makes them thirsty as hell. One conservationist I spoke with when reporting on WNS way back in 2017 described finding bats outside in the dead of winter, trying to sip water from snow and ice. They don’t make it back into their caves.

WNS is so contagious among the bats, many species of which spend their winters cuddled as tightly together inside a warm cave as possible, that its spread basically cannot be stopped. Some hibernacula see lethality of 99 percent in a single year; some disappear entirely. The disease ballooned outward from New York, quickly inundating the New England states before spreading through the Midwest and eventually jumping all the way to Washington state, and then other mountainous regions of the West.

It is, undoubtedly, a wildlife tragedy of epic proportions. It does, however, provide a macabre sort of opportunity: the “ecosystems services” that bats provide could now be examined in a before-and-after framework — when WNS arrives, it is hard to miss, so the demarcation line between a healthy bat population and an unhealthy one is clear. This is just what Eyal Frank, an environmental economist at the University of Chicago, has done, publishing a paper last week in Science examining the effects of WNS on agricultural and economic outputs, as well as on human health. His findings are as dark as the canvas they’re drawn on.

“Disruption to biological pest control has a meaningful impact on human well-being,” Frank wrote. “I demonstrate how declines in insect-eating bat population levels induce farmers to substitute with insecticides, consequently resulting in a negative health shock to infant mortality.”

The numbers here are indeed shocking. In agricultural counties where WNS sent bat populations plummeting, he showed that farmers increased insecticide use to compensate for the decline in predation — an increase of more than 31 percent. In absolute numbers, the total volume of insecticide increase was not enormous — about 2.7 extra kilograms per square kilometer. But that seems to be enough: infant mortality in those regions also increased in the post-white nose period, by 0.54 deaths per 1,000 births. That’s an increase of almost eight percent.

In a separate commentary in Science, experts led by Ashley Larsen of UC Santa Barbara called the bump in both insecticide use and infant mortality “shockingly large.” To be clear, this is still just evidence of correlation, not of causation — but it isn’t so unreasonable to imagine that increasing the volume of chemicals used on crops might have negative health effects on the people around them. Other studies, including one published in February 2023, found increasing use of the common herbicide glyphosate was connected with a five percent increase in infant mortality in the surrounding area.

Further, Frank’s analysis separated out “internal” and “external” causes of infant mortality. External causes include accidents and homicides, deaths that would not logically be connected to a decline in bat populations and subsequent increase in pesticide use — and they weren’t, at all. In a further grim demonstration, those unchanged external causes, Frank wrote, act as a sort of placebo for comparison to the substantially increased internal death rate. He did not find any changes to birthweight, gestation, or other measures of newborn health, but Frank noted that other studies of environmental pollution have found similarly that mortality can go up even when those other metrics seem unchanged.

Beyond the heartbreaking health effects, the economic damages are significant. Frank estimated that the 2006 to 2017 period saw agricultural losses directly attributable to WNS of almost $27 billion; other estimates have offered similar orders of magnitude.

The study is bursting with obvious-but-quantified messages. Protect wildlife, protect economic output, protect human health — to almost absurd degrees, as it turns out. “If the costs of conserving bat populations are low and damages from our currently best-available substitutes for their biological pest control—pesticides—are high, then conserving bats can be beneficial for society,” Frank wrote. Stopping the spread of WNS is remarkably difficult, of course, if not impossible at this point; but trying to reduce the other pressures on bat populations, from deforestation and land use change to climate change, offers obvious benefits that likely extend to plenty of other types of wildlife out there.

And the human impulse to turn to a technological solution in the face of any problem — in this case, peppering the landscape with insecticides to replace the swirling predators above — is laid bare once more as a fool’s errand. “The technological race is rarely won,” wrote Larsen and her colleagues, noting that in this case the “solution” might result in pesticide-resistant bugs or otherwise altered crops, sparking yet another turn in the arms race. “Although it is near impossible to fully quantify the ecosystem and welfare losses of such widespread declines, stemming the biodiversity crisis is crucial to maintaining the many benefits that ecosystems provide for which technological substitutes cannot readily, or perhaps, ever replace.”