Lethal White-Nose Syndrome Reaches Canada’s Northernmost Bat

Scientists crawling through a narrow cave passage beneath a boreal forest near Fort Smith in Canada’s Northwest Territories in May discovered evidence that a deadly fungal disease has reached the northernmost-known bat hibernation site in North America. Two biologists spotted a lifeless bat on a limestone ledge, its body covered in spindly white fungus, marking a grim milestone in the spread of white-nose syndrome.

Jesika Reimer, an ecologist specializing in bat populations in northern Canada and Alaska, confirmed the diagnosis after seeing another bat with fungus on its forearms in the same cave. “It hissed at us and crawled back into a crack,” Reimer says. The discovery came as a shock to researchers who had hoped to complete baseline surveys of healthy populations before the fungus arrived. Fort Smith sits approximately 450 miles south of the Arctic Circle, and scientists thought they had at least one or two more years before the disease reached this far north.

White-nose syndrome, caused by the fungus Pseudogymnoascus destructans (known as Pd), has swept westward across North America for 20 years, spreading from bat to bat and cave to cave. The disease has killed more than 6.7 million bats since it began its deadly march across the continent, and now scientists face urgent questions about its potential impact on bat populations in Canada and Alaska.

How the Fungus Kills Bats

The fungus attacks bats’ faces, wings, and arms while they hibernate in winter caves. Infected bats stir from rest and groom themselves, burning through the fat and energy reserves they need to survive the winter. The animals eventually die from dehydration or starvation, with smaller bats facing particularly high risk due to their lesser fat reserves. The disease strikes when bats are most vulnerable, disrupting the natural hibernation cycle that allows them to survive harsh winter conditions.

“For 20 years, we’ve been tracking the spread of white-nose syndrome across the continent,” says Joanna Wilson, a biologist for the Northwest Territories government and colleague of Reimer. “We always knew it would eventually get here.” In 2025, white-nose syndrome appeared in a cave in Fort McKay, Alberta, nearly 200 miles south of the Fort Smith location. “We thought we’d have a year or two,” Reimer adds.

Discovery of Northern Bat Caves

The caves near Fort Smith where scientists made their grim discovery were first identified in 2010, when a wildlife technician flying over the area noticed a distinctive karst feature below. A karst landscape forms when bedrock such as limestone or dolomite dissolves, creating underground caves and sinkholes that provide ideal habitat for wintering bats. The technician later hiked back on foot and confirmed the site was indeed a hibernaculum, a shelter where bats spend the North American winter. Scientists subsequently found two additional caves in the region.

Until that discovery, biologists did not know where the Northwest Territories’ hibernating bat species-including little brown bats-spent their winters. The identification of these northern hibernation sites represented a significant breakthrough in understanding bat ecology in subarctic regions. Fort Smith now holds the distinction of hosting the northernmost-known hibernaculum in North America, making the arrival of white-nose syndrome at this location particularly significant for researchers tracking the disease’s spread.

Racing Against Disease Spread

The discovery underscores the challenge scientists face in studying and protecting bat populations ahead of the fungus’s relentless advance. Researchers had planned to conduct thorough baseline surveys of healthy, stable bat populations before white-nose syndrome arrived in the region. These surveys would have provided crucial data for measuring the disease’s impact on northern bat colonies. The unexpectedly rapid arrival of the fungus in Fort Smith caves eliminated this opportunity, forcing scientists to adapt their research strategies on the fly.

The fungus spreads through direct bat-to-bat contact and environmental contamination in caves where infected bats hibernate. Once Pd establishes itself in a hibernaculum, it persists in the environment, threatening successive generations of bats that return to the same winter shelter. The disease has devastated bat populations across eastern and central North America, with some species experiencing population declines exceeding 90 percent in affected regions.

Implications for Northern Ecosystems

Bats play essential roles in northern ecosystems, consuming vast quantities of insects during warmer months. A single little brown bat can eat up to half its body weight in insects each night, providing natural pest control for forests and agricultural areas. The loss of bat populations to white-nose syndrome carries cascading effects throughout ecosystems, potentially leading to increased insect populations and reduced forest health. Scientists worry that the disease’s arrival in these northern hibernacula could devastate bat colonies that have no previous exposure to the fungus and therefore lack any evolved resistance.

The confirmation of white-nose syndrome at Fort Smith marks a turning point in the disease’s expansion. With the fungus now established at the northernmost hibernation sites, researchers face the sobering reality that few, if any, North American bat populations remain beyond its reach. The race to understand and potentially mitigate the disease’s impact becomes more urgent as it advances into previously untouched regions.