Fireflies and the allure of light

By R. Gary Raham:

As sunlight fades on a warm summer evening, there is something magical about lights floating through the air blinking secret messages. As a kid growing up in Michigan, I soon discovered that flying beetles called fireflies (or lightning bugs) produced those pulsing lights and, better yet, that I could capture them in an empty glass jar! Heady stuff for a nerdy kid fascinated enough with nature that he would eventually become a biologist.

I thought I had left these fascinating creatures behind when I moved to Colorado as a young adult in 1969. Not so. Colorado does harbor populations of fireflies, although scientists still don’t have a clear picture of all the species that live in our state. One has to seek out the wet habitats fireflies like and visit them between late June and early July. That’s when they flash light messages back and forth to each other—announcing a mixture of danger, desire, and deceit. But before exploring these “3-Ds,” it helps to know more about this insect’s body plan and how it uses light to communicate. Someday you may want to find Colorado fireflies for yourself, if chasing floating lights captures your imagination as it does mine.

Misnamed flies, fireflies are really beetles—an ancient form of insect that accounts for 40% of ALL insects and 25% of ALL animals. Beetles have two pair of wings, but the outer most wings (elytra) are hard and fold up to cover the back of the creature like the hood of a car engine. When beetles fly, the elytra lift up to let the delicate underwings do all the aerodynamic work. Beetles navigate like flying tanks, which allows kids to capture them in glass jars. Beetles have three body parts, like all insects: Head, thorax (to which six legs attach), and abdomen (divided into segments). Typically, the last one or two abdominal segments of a firefly are called the lantern, and that is the organ that produces the firefly’s bioluminescent (and 100% energy efficient) glow.

Beetle eggs hatch into hungry, worm-like larvae. All firefly larvae can glow with bioluminescence, but not all species of adult do. This may reflect the fact that light emission may have started as a warning to would be predators that “DANGER: I don’t taste good. I might even kill you, if you eat me.” When larvae have eaten their fill, they transform into an overwintering dormant phase called a pupa. Pupae metamorphose into adults, who need to find suitable mates to complete the cycle. Over the course of time, many species of adult fireflies co-opted light emission as a signaling device between males and females.  (The DESIRE part of the 3-Ds)

Some female fireflies used their light flashing skills for DECEIT. What better way to get a good meal than to attract the male of an alien firefly species using his own species’ “love language” as a lure?  For example, in the Midwest, female Photuris pennsylvanica lure male Photinus pyralis males into their clutches. Other firefly species are content to eat snails, worms, or slugs, injecting them with numbing chemicals from their metabolic arsenals to subdue them. A few species eat nectar or pollen or forego food altogether in the pursuit of amore.

Just as scientists learn more about Colorado fireflies, they are dwindling because of habitat loss and light pollution (which muddies their ability to communicate). Fortunately, The Butterfly Pavilion (located at 6252 W. 104th Ave., Westminster, CO) has initiated a project to rear fireflies in their lab. They are also looking for citizen scientists to add to their database about fireflies (See https://butterflies.org/firefly-rearing/).

Scientists from the Butterfly Pavilion captured some fireflies for their breeding program last year at a City of Fort Collins Natural Area program called “Light up the Night,” first initiated by volunteer naturalist, Elizabeth Kittrell in 2020. The City has two of these programs this year at Riverbend Ponds in Fort Collins on Thursday, June 27 and Tuesday, July 2. Contact Samantha Troi (stroi@fcgov.com) for more details or check out all the programs the city offers at https://www.fcgov.com/naturalareas/. I’ve been a volunteer for the natural areas myself since 1995, but somehow missed this new program. Not this year. I plan to admire the light show these amazing beetles perform and perhaps relive some of the fascination with the allure of light that I experienced so long ago.

Gary Raham is a biologist who writes both science fact and science fiction. Not Quite Dead Geniuses at Large on an Angry Planet is a 2024 Colorado Book Award Finalist.