Dark field with fireflies. Photo: Peggy Campbell.
Story by Mark Banaszak. Photos by Peggy Campbell.
Imagine you’re 10 years old. It’s somewhere between late June and late July. You’ve been sent outside at dusk because it’s too nice to be inside. You think about nothing in particular as you run around with an old jar catching fireflies. It is best not to focus on any one thing in the landscape, so you can watch a larger area for flashes. You wait for one to light up — from its hind end. You’re close enough to scoop the insect’s body into the jar and cover it with your hand before the bug’s glow fades. But, if you don’t get there in time, you might find yourself squinting in the fading daylight at the darkened beetle as it hovers in the air, just out of reach.
Slow-flying insects, fireflies often stay near, but not at, the spot where they last lit up.
As an adult, you are more likely to be sitting on a deck or near a window when you notice the flashes spread across a field. At first, the field seems dark. After you see a few flashes, your eyes begin to adjust to the fading light and can focus on a wider expanse. Now you perceive many pinpricks of light across a large area. The effect is magical — floating winks of light, random and ephemeral, spread across a dark landscape.
How does it work that a creature can make light with its body? Why do they do it? Collecting specimens in jars or watching them from your deck is a fun pastime, but fireflies have significance beyond just being beautiful.
Fireflies make light, called bioluminescence, through a chemical reaction involving oxygen and other substances. This reaction is described in “How and Why Fireflies Light Up,” by Marc Branham, in Scientific American, Sept. 5, 2005. At the time of the article, Branham was an assistant professor in the University of Florida’s department of entomology and nematology. He described the resulting light as “cold,” that is, not emitting a lot of heat. If the chemical reaction producing the light gave off intense heat, the firefly would die.
Fireflies glow for a number of reasons, according to the same article. In its larval stage, the firefly’s light warns predators that they’re unpalatable. Adult species have different flash patterns, so they can find one another and discern males and females.
It’s important to know that there are many species of fireflies in the world. Two common species in Michigan are big dipper fireflies and spring tree-top flashers. The time of year they appear may overlap a bit, but the tree-top variety tends to be earlier in the spring, is seen high in the tree canopy, and has single, short, amber flashes every two or three seconds. The big dippers have a longer flash about every six seconds and fly upward in a distinct “J” shape. It is generally males you see hovering over fields; the females are usually down in the vegetation, safe from predators, and signal back with shorter, single flashes.
Biodiversity within a single insect family carries real ecological weight. Many species of fireflies naturally control pests and help keep ecosystems resilient. Fireflies eat the worms, slugs and snails, often plaguing gardeners’ plants and farmers’ crops. Multiple species with similar roles in an ecosystem mean that challenges like disease or climate change are less likely to wipe them out. There are an estimated 24 species of fireflies in Michigan. They have a variety of characteristics and fill a variety of roles — meaning that if one species fails, another may be able to step in and fill the gap.
Biologists widely consider them an indicator species, meaning the presence of fireflies signals a healthy ecosystem, and their absence signals problems. Their complex bioluminescent compounds have even found use in medical research, helping scientists pinpoint where and when specific biological processes are occurring, a kind of natural flare in the lab.
Most importantly, fireflies are vulnerable to change brought about by humans. Increased artificial light at night disrupts the lifecycle of many nighttime creatures, and fireflies are a prime example. They become disoriented by bright artificial lights and may fail to find mates, leading to documented population declines in heavily lit areas.
Some of us humans fled the city, in part to experience the benefits of nature. According to the American Association for the Advancement of Science, more than one-third of the world’s human population can no longer see the Milky Way in the night sky, and 80% live with some degree of light pollution. The fix, fortunately, is simple: Turn off lights when you don’t need them. The fireflies will appreciate it, and so will your neighbors.
Read more about the importance of darkness at night in the fascinating book, “Night Magic: Adventures Among Glowworms, Moon Gardens and Other Marvels of the Dark,” by New York Times bestselling author Leah Ann Henion. (Special thanks to Susan Schankin for donating copies of the book to community members.)
Mark Banaszak has spent more than 30 years as a public-school educator, urban community gardener, and outdoor enthusiast. He transplanted his city life to rural Manistee County. Peggy Campbell is an area photographer. Her work was recently exhibited at Oliver Art Center in Frankfort.
