When bats were wiped out, more human babies died, a study found. Here's why

A deadly pandemic has decimated bats in North America — and that has ultimately had harmful effects on humans, including higher rates of infant mortality, according to a new study.

The research is part of growing evidence that humans rely on the animal and plant species around them, and are harmed when those species decline or go extinct.

White-nose syndrome is a deadly fungal disease that kills an average of 70 per cent of bats it infects, and has been spreading to new areas since it was first reported on the continent in 2006.

The disease wakes bats during their hibernation, often causing them to freeze and starve to death.

Ecologists know that bats play a crucial role in eating up and controlling insect pests.

Because of that, Eyal Frank, an environmental economist at the University of Chicago, decided to look at what happened when white-nose syndrome spread into new counties in the eastern U.S., decimating bat populations.

He found that farmers responded to the resulting insect outbreaks by increasing their pesticide use 31 per cent. Pesticides are toxic, and often associated with human health impacts such as increases in infant deaths.

Frank found that infant mortality went up eight per cent after the arrival of white-nose syndrome in a county, according to his study published today in the journal Science.

"At first I was surprised," Frank said, noting those increases are "big effects."

But he noted that in regions affected by white-nose syndrome, bat populations don't just decline, but plummet, and are often wiped out altogether.

"This is really turning off the switch on biological pest control in some of these counties," he said.

That forces farmers to compensate with "a lot more insecticides," which he notes are toxic by design.

Frank also found evidence that not only were the pesticides expensive, but they weren't as good as the bats at controlling insects — farmers' revenue from crop sales fell 29 per cent in areas hit by the bat pandemic.

He estimates that in total, farmers in communities with bat die-offs lost $26.9 billion between 2006 and 2017. Putting a number to damages from infant mortality resulted in a societal cost of $39.6 billion from the loss of bats.