Scientists Identify Surprising Link Between Infant Mortality Rates and Bat Populations

Searching for an explanation for a rise in infant mortality led scientists to a unexpected answer

Hiya!

“Everything is connected" is a phrase we’ve heard repeatedly from philosophers and hipsters to mystics and poets. It’s usually linked to things like karma and relationships, and especially to nature. Yet, despite the undeniable, albeit subtle, seed of Truth in the phrase, this wisdom is often ignored or dismissed as mystical nonsense with minimal real-world applications.

But, as with so many other things discussed in this newsletter, scientific advancements now allow scientists to investigate some of our long-dismissed ancient teachings, and they’re discovering many hold more Truths than we realized.

Today’s topic is a prime example. A scientist linked a rise in infant mortality in the United States to the decline of bat populations. This is just the most recent research revealing the intricacies of our connection with Nature and how crucial healthy ecosystems are for our well-being.

White-Nose Syndrome

Let’s start from the beginning. In 2006, Pseudogymnoascus destructans, a fungus nicknamed White-Nose Syndrome, caught a ride from Europe to the United States via Albany, New York.

As you can see in the image below, the fungus grows as a white fuzz on bats' exposed skin, especially around the nose (hence the nickname), as they hibernate in winter.

Image Credit: Marvin Moriarty/USFWS — Source: WikiCommons

White-nose syndrome disrupts bats’ sleep, waking them when they should be resting. Fighting the fungus requires enormous energy, which is needed to keep the bat alive during the winter. With their energy levels depleted, infected bats typically end up starving or freezing to death.

The fungus has already killed millions of bats and can wipe out an entire colony in just five years. Conservationists report that some bat species, including the northern long-eared bat, the little brown bat seen in the image above, and the tri-colored bat populations, have declined by over 90 percent within the last decade.

Unfortunately, the fungus has continued spreading across North America since arriving in 2006. As of 2024, white-nose syndrome has been found in at least 40 U.S. states and nine Canadian provinces. As terrible and heart-wrenching as white-nose syndrome is for bats, Eyal Frank, an assistant professor at the University of Chicago, linked the fungus to another string of devastating fatalities — human infants.

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Initial Curiosity

When Frank, an environmental economist, learned about white-nose syndrome, he saw an opportunity to demonstrate the value of bats. Frank told Catrin Einhorn of the New York Times:

“Reading how this disease is spreading from county to county, decimating bat populations, made my economist senses go, ‘Oh, this is probably the best natural experiment you can have,’ It’s the closest we’re going to get to just going out there into the wild and randomly manipulating bat population levels to see what happens at a large, meaningful spatial scale.”

See, every night, bats consume 40 percent or more of their body weight in insects. This means a single bat can eat thousands of insects every night — several hundred in an hour. Crucially, much of their diet includes crop pests. So, Frank wondered, what might happen if bats disappear?

He reasoned that if bat populations fade in agricultural areas, farmers might use more insecticides on their crops. Frank jumped on the opportunity to investigate his curiosity and then published his findings in Science on September 06, 2024.

Initial Analysis

To search for answers, Frank, the study’s sole author, analyzed data from agricultural censuses in the United States and compared counties where white-nose syndrome had been detected with counties it hadn’t yet presented up to 2017, which is when the census data stopped as it’s released only every few years.

Analysis Results

Frank discovered that farmers in infected areas compensated for the drop in bat populations by significantly increasing their insecticide use by an average of 31.1 percent.

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Delving Deeper

These results supported Frank’s suspicions, but instead of satisfying his curiosity, the information deepened it. What large-scale effects might result from farmers significantly increasing their use of insecticides to compensate for the loss of bats?

One of the most obvious starting points is the financial outcome, as farmers would need to spend more money to buy more insecticides.

Financial Cost

To learn more, Frank evaluated the losses attributed to declines in bat populations in infected counties and estimated the total agricultural losses, including crop revenue and chemical expenditures.

Frank writes in the study that between 2006 and 2017, the counties with bats infected with white-nose syndrome lost “$26.9 billion (2017 dollars)” due to lower crop sales and increased insecticide costs. [Fun fact: $26.9 billion in 2017 is over $35.8 billion in 2024.]

The costs related to buying more insecticides when they’re using more makes sense, but the loss of crop sales is less clear. Frank hypothesizes that crops without bats and with increased insecticide use may produce lower-quality produce that doesn’t sell as well.

Frank’s findings are supported by another study, one from 2022, which linked a drop in farmland rental prices to the spread of white-nose syndrome in bats. The researchers’ theory is that without bats providing free pest control, farmers have to spend more money to grow their crops or have lower yields, making the land less valuable.

Cost of Life

Unfortunately, Frank found that the financial cost isn’t the only cost of increased insecticide use. He decided to examine infant mortality rates since plenty of research (which I’ll tell you about later) links adverse human health effects to insecticides and pesticides.

It might seem a strange statistic to jump to, but infant mortality rates (excluding deaths due to accidents and murders) are often used to estimate the impact of environmental toxins.

Results

After analyzing the data, Frank discovered that infant mortality rates in infected counties were an average of 7.9 percent higher than in counties with healthy bats — even though the increased insecticide use was within federal regulatory limits. More specifically, he calculated that an additional 1,334 infants died by 2017 within the infected counties.

Despite the connection between higher insecticide use and increased infant mortalities, Frank is unable to explain how, exactly, the insecticides might cause the deaths. He told Michael le Page of New Scientist:

“I can’t say anything about the direct exposure mechanism, only that my results are not consistent with the idea of exposure through food.”

If infants aren’t consuming the insecticides through their food, they might be drinking it via contaminated water or breathing it in from the air.

Still, it’s important to consider other possible explanations, even when the evidence suggests you’re right, which is why Frank tested for other potential factors that might plausibly explain the spike in infant deaths.

He looked at any new genetically modified crops in the infected areas, unemployment rates, the opioid epidemic, and even the weather conditions around the mothers during their pregnancies. Still, none of them explained the rise in insecticide use or infant mortality rates.

Frank told Rebekah White of The Guardian that he spent a year “kicking the tyres on the study,” but the results held. His research, he explained, provides:

“compelling evidence that farmers did respond to the decline in insect-eating bats, and that response had an adverse health impact on human infants”.

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Convincing Link

As astonishing and explicit as Frank’s research is, it isn’t all that surprising. Researchers have been sounding the alarm over the harmful effects agricultural chemicals have on human health for years.

That said, Frank’s study stands apart from previous research by providing not just a correlation but also a causation between a rise in insecticide use and infant mortality, according to Charles Taylor, an environmental economist at the Harvard Kennedy School, who was not involved in the study. Taylor explained to White how,

“A lot of papers that try to link pesticides to outcomes are correlational in nature. People who are exposed to more pesticides, for example, might have other risk factors – like, farm workers are exposed to a whole host of other socioeconomic risks that could explain why there might be different health outcomes.”

But this is why Taylor thinks Frank’s findings are “quite rare.” He goes on to say:

“[T]o get good, empirical, grounded estimates of how much value the species is providing, putting actual numbers to it in a credible way is tough.”

Frank’s study might be the most convincing link between a rise in insecticide usage and infant mortalities due to a decrease in bat populations, but it’s far from the first to suggest connections between collapsing wildlife populations and the unexpected domino effect for humans.

I considered tossing a few links to some of the studies I’m referring to in the last paragraph since discussing them will only make this already lengthy article longer. But I’m me, and this is my newsletter, so I decided to talk about four in particular. Feel free to skip ahead if you’d rather though.

Supporting Evidence

While not quite as clear-cut as Frank’s analysis, previous research — including Frank's own prior work — has discovered an array of surprising outcomes a decrease in wildlife populations has on human health.

One

In June 2024, just a few months before his white-nose syndrome study, Frank and Anant Sudarshan, an associate professor at the Department of Economics at the University of Warwick and a Senior Fellow at the Energy Policy Institute at the University of Chicago (EPIC), published a study in the American Economic Association.

The duo linked the collapse of India’s vulture population to a 4 percent rise in human mortality — an estimated 500,000 human deaths — and calculated the cost of related damages to a staggering $69.4 billion per year. Frank and Sudarshan believe that infections like rabies increased without vultures to eat rotting meat.

Two

Besides Frank, other researchers discovered evidence in 2021 that wolves’ hunting habits help keep deer off roads and thus help limit car accidents.

Three

Also in 2021, Taylor published a study on cicadas, a flying grasshopper-like insect that remains mostly underground except for emerging en masse every 13 to 17 years. He discovered that farmers increased their pesticide use during cicada seasons when they emerged from below ground — and that infant mortality rates rose in the same years.

Remarkably, Taylor also found that people born during the cicada years had lower test scores in school and were more likely to drop out before graduating high school.

Four

Lastly, David Rosner, a history professor at Columbia University who has spent decades investigating environmental toxins, told White of The Guardian that Frank’s research is the latest in many studies going back to the 1960s showing adverse effects of pesticide use on human health. He said:

“We’re dumping these synthetic materials into our environment, not knowing anything about what their impacts are going to be. It’s not surprising – it’s just kind of shocking that we discover it every year.”

And yet, little to nothing is done to address it.

Perspective Shift

We’ve spent millennia forgetting our connections with Nature as we progressively isolated ourselves within concrete jungles. For many, Nature is an attraction to visit or has been shrunk down and contained within a personal garden that we manicure and manipulate to our liking.

But with climate change, Nature is forcing us to remember that we are not in control of Her, nor are we an isolated species on this planet excluded from responsibility or the repercussions of our choices. After all, we may not be directly responsible for the white-nose fungus decimating bat populations, but our chemicals are responsible for the rise in infant mortality rates.

Perhaps a shift in perspective, especially in the West, is needed in addition to studying the domino effects of wildlife collapse. Much of the research focuses on how we’re affected by the demise of another species, but maybe we should also focus on our role in all of it.

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Photo by Zdeněk Macháček on Unsplash