Blinded by the light – Protecting Minnesota’s natural pest control
– Dawn Ryan
You might not see them working, but bats are busy every night keeping Minnesota’s insect population in check—if we let them.
Artificial Light at Night (ALAN) – what humans are doing to light up the planet at night - is considered a threat to biodiversity very broadly; it impacts plants, insects, and animals including humans. Not surprisingly, bats, are included in this list of affected animals. Bats are adapted for the dark, using special senses and nighttime habits to survive—but artificial light at night can throw off their routines, weaken their health, and make it harder for them to survive. Recent research showed that white LED lights commonly used in residential areas can disturb two bat species found in Minnesota, the little brown bat and the big brown bat, already struggling with white-nose syndrome. These lights don’t just affect the area they directly illuminate—they cause bats to avoid much larger surrounding areas, leading to noticeable changes in which bat species are present in those habitats. Bats can eat nearly their body weight in mosquitoes and agricultural pests each night. Fewer bats mean more insects, increased insecticide use, and a less balanced ecosystem, which can affect everything from crop health to summer evenings outdoors.
Because bats must build up all their fat reserves before hibernation, anything that limits their feeding time—like avoiding brightly lit areas—can leave them with less energy to survive the winter.
Bats face more than bright lights
As if artificial light weren’t enough, bats are also battling a deadly disease. Since it arrived in the U.S. around 2005, white-nose syndrome (WNS) —a deadly fungus—has been devastating bat populations across the country. The fungus appears on the bats’ muzzle and wings and interferes with their hibernation, causing them to wake up when they should be conserving energy. Even a single disturbance during winter can burn through a bat’s fat reserves, leaving it without enough fuel to survive until spring. WNS arrived in Minnesota in 2015 and by 2016 to Mystery Cave in Forestville/Mystery Cave State Park. This cave serves as a major hibernaculum for four species of Minnesota bats. At peak, hibernating bat counts in Mystery Cave produced about 2,400 bats. Within the two years the fungus appeared in the cave, nearly 95% of the caves hibernating bat population disappeared. Similar die-offs were observed at other Minnesota hibernaculum such as Soudan Underground Mine State Park. Artificial lights cut into bats’ feeding time, and White-nose Syndrome drains their energy—together, these threats leave bats with too little to survive the winter.
Hope in the night
While the challenges remain, ongoing conservation work and growing community support are helping bats recover in some areas. After years of decline, bats may finally be turning a corner—thanks to the combined efforts of scientists, land managers, and public stewards. Recent projects on public lands across Minnesota—including the installation of a variety of bat boxes, allowing standing dead trees to remain, and changes in timber harvests—have been improving habitat options for bats. Local advocates and communities can help too. Small changes—particularly dimming yard lights—add up when entire communities get involved.
A darker night for us means a brighter future for bats. Take a small step today—dim the lights, protect their roosts, and help bats thrive in your corner of Minnesota. Together, we can help protect Minnesota’s dark skies and its bats flying strong.
Dawn Ryan
Mystery Cave Manager 🦇
Forestville/Mystery Cave State Park
21071 County 118
Preston, MN, 55965
Phone: 507-808-8010