Lights Out: The Effects of Light Pollution on Pollinators, the Indiana Bat, and other Threatened Species
By Saige Sentell, Education Director
Dust filled the air one evening in June as cars entered the Beanblossom Bottoms Nature Preserve parking lot. Dressed in various shades of brown and green, the Native Plant Nursery volunteers, Sycamore staff, and a few board members gathered for an enchanting night chasing fireflies. Dr. Sérgio Henriques, the invertebrate conservation coordinator for the Indianapolis Zoo, met everyone with a smiling face and a tale of the cyress firefly (Photuris walldoxeyi), one of the rarest of the 44 species of lightning bugs found in Indiana with only two documented locations, one of which being Beanblossom Bottoms Nature Preserve.
The sun fell as Sérgio explained how firefly flash patterns are unique to each species, and that the cypress firefly flash consists of “four to nine bright pulsing flashes followed by a prolonged one second glow” (Xerces Society). When a female sees a male firefly making her species’ signal, she flashes back with a species-appropriate flash of her own. The two signal back and forth as the male flies down to her.
Cypress firefly at Beanblossom Bottoms, Photo by Sérgio Henriques
According to Sérgio, the Myaamiaki (Miami People) name for firefly is “wa-wa-see-wa,” which probably refers to the flight and light pattern of the cypress firefly, leading scientists to believe that prior to the colonization of Indiana, this may have been one of the dominant species found in our state. This species, now listed as threatened, can be spotted by their flash at Beanblossom Bottoms from mid-May to mid-June in the evening hours before the preserve closes to the public at sunset.
As volunteers and staff walked through the wetlands on this special night hike, guided by the moon’s glow, our eyes adjusted to the darkness and allowed us to identify these little creatures. During our evening with Sérgio, which was near the end of their breeding season, we found a population dancing above the boardwalk. We counted their flashes, laughing with excitement, finding this rare firefly amongst the others. Under the cover of night and protected by the nature preserve, these unique and fascinating creatures are able to find each other. Cypress fireflies, Indiana bats, and other pollinators are able to thrive at Beanblossom Bottoms without the harmful effects of artificial light.
Light pollution, defined as the “excessive or inappropriate use of outdoor artificial light,” is a problem affecting human health and wildlife behavior, specifically migratory birds, pollinator insects, bats, and other mammals. It can be broken down into four categories: glare, sky glow, light trespass, and clutter. Glare refers to any light that causes visual discomfort. Sky glow is the overall brightening of the night sky due to urbanization. Light trespass is light falling where it should not, and clutter refers to bright, confusing, and excessive groupings of light sources.
According to Dark Sky International, 99% of the U.S. population lives under sky glow, meaning nearly all Americans can’t experience a natural night. Sadly in Indiana, there are no “dark sky” areas. However, Beanblossom Bottoms, which is nestled just far enough away from Bloomington, can offer spectacular views of the night sky and provides habitat for wildlife and pollinators, like the Indiana bat and the cypress firefly.
Little Brown Bat. Photo by Ann Froschauer, USFWS
Light pollution, especially clutter and light trespass, disrupts the natural rhythms of pollinators, like bats which rely on darkness for navigation and foraging. Light affects a bat’s ability to hunt in a myriad of ways. Although light does not directly impact echolocation, it does change insect behaviors by attracting them to bright light, making it harder for bats to locate prey. In a study conducted by Bat Conservation International, the hoary bat and the eastern red bat did not change their behaviors based on light pollution; however, their presence in these lit areas made them more vulnerable to predation. In contrast, little brown bat populations were reduced by 48-75% when light was introduced to their habitat.
It is important to record how varying species react to excessive light. Artificial light at night, or ALAN, can change the bat composition at a site, keeping some away while attracting others. When bats avoid an area due to light, it limits the habitat they can use for foraging, roosting, and mating (Pope). ALAN may reduce the already-limited habitat available to light-sensitive species, such as the Indiana bat which is already imperiled by white-nose syndrome. According to the U.S. Geological Survey, mortality rates of 95% were observed in some Indiana bat hibernacula. Light pollution and reduced habitat coupled with white-nose syndrome has landed this species on the endangered list. However, thanks to the shaggy bark of newly dead trees and the bountiful bugs that inhabit the bogs of Beanblossom, the Indiana bat has been found and monitored on our preserve.
Not only does artificial light impact pollinator behavior, but it also has cascading effects on ecological processes and the overall health of native ecosystems. Light pollution can lead to decreased rates of plant pollination, leading to reduced plant reproductive success, decreased seed germination, altered flowering times, and a decrease in biodiversity. These effects have significant impacts on ecosystem balances; changes in plant behavior and growth can ripple through the ecosystem, affecting herbivores and higher trophic levels that depend on native plants for food. In addition, light pollution can put even more stress on pollinators who have already reduced habitat due to fragmentation and loss.
How You Can Help
Luckily, there are a few steps that every Hoosier can take to reduce light pollution. In your home, choose outdoor lighting that directs light downwards, and install motion sensors to minimize unnecessary lighting. Select LED bulbs with low brightness and a warm color temperature while also minimizing glare. At night, turn indoor lights off or cover windows with blinds or curtains. With more people on the planet than ever before, there’s no doubt that one of the largest factors contributing to light pollution is urbanization. Encourage city planners and policymakers to choose lighting and initiate practices that favor natural light and reduce sky glow, light trespass, clutter, and glare. Artificial light at night disorients migrating birds like the black and white warbler and the yellow-bellied sapsucker, luring them toward and into urban centers. Once birds land near buildings, they are at increased risk of glass collisions, one of the most significant human-caused threats to birds in North America.
Cities across the U.S. like Chicago participate in “Lights Out” efforts during migration season, significantly reducing bird mortality. But cities can’t do this alone. Coordinated efforts at the local, regional, and national levels are needed to protect our pollinators from light pollution. Urban areas will continue to be developed and our birds, bats, and other pollinators will continue to pass through these spaces. It is up to us to make this journey as safe as possible through a reduction in artificial light.
For more information regarding the Indiana bat, the cypress firefly, birds, moths, and other pollinators, attend an educational workshop or hike with Sycamore!
This article is from the Fall 2024 issue of The Twig, “The Indiana Bat Issue.” Read the issue at sycamorelandtrust.org/twig
