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Nov 09, 2023

Fireflies thrive in Colorado wetlands. Scientists shed light on why.

On a recent trip to Illinois, Charley LeCrone took his wife and two young daughters to see the fireflies he remembered fondly from childhood. But when dusk fell, the fireflies’ blinking yellow-green

On a recent trip to Illinois, Charley LeCrone took his wife and two young daughters to see the fireflies he remembered fondly from childhood. But when dusk fell, the fireflies’ blinking yellow-green lights failed to appear.

Fireflies don’t live there anymore.

Fireflies need a fresh, moist environment to thrive, which is why they are widespread — but also under threat — across much of the eastern United States. But unbeknownst to many, fireflies also thrive in scattered oases across Colorado and can be seen flashing their mating calls in wetlands for a few short weeks in June and July.

LeCrone and his family got a second chance in Colorado, catching a glimpse of flashing fireflies as they floated across the landscape on a recent summer night at Riverbend Ponds Natural Area on the outskirts of Fort Collins.

“A lot of native Coloradans have never seen a firefly, don’t even know they exist out here,” Beth Kittrell, a volunteer for Fort Collins Natural Areas, said as she led a firefly tour through a maze of reclaimed gravel pits north of Prospect Avenue.

Fort Collins Natural Areas started its “Light Up the Night” tours three years ago. They are now one of its most popular activities, with a long waitlist. Fireflies were identified in 2018 near Loveland and the city now has its own “Fireflies in the Meadow” programs in July, although visitors can try their luck alone at the Morey Wildlife Reserve at the western edge of the Mariana Butte golf course.

Other reported sightings in recent years range from Greeley to Pueblo on the Front Range, and in several mountain valleys near Moffat, Divide, Durango and Carbondale. Two research programs are studying fireflies in Colorado, and several community-science projects are discovering fireflies at more and more locations.

As lightning flashed from thunderheads on the horizon, volunteer Kittrell explained to the 20 or so participants that fireflies are not flies, but beetles with a complex life cycle that progresses over one or two years from egg to larva, pupa and adult firefly, which lives for only a few weeks. The fireflies flashing a few feet above the ground are males signaling prospective mates lingering on the ground.

There are about 165 species of fireflies in the United States and Canada, each with its own species-specific flashing pattern. When a receptive female recognizes the flash pattern of her own species, she flashes back to the eager male. But male fireflies, beware! Females of some species are known to flash patterns of other species to attract those males, which they then kill and eat.

From a parking lot near the Cache La Poudre River, the group headed out on a gravel path between the ponds, then onto a boardwalk that traverses a rich, open wetland of tall grasses, rushes and other water-loving plants. As darkness descended, the first flash appeared just off the boardwalk. Soon dozens of fireflies were flashing across the wetland.

“Best day ever!” exclaimed Hannah Brown, a member of a Butterfly Pavilion team that had come to collect fireflies for an ongoing research project. She was thrilled to see the magical fireflies she first saw as a college student in New York. She was also happy to know that the research team would be able to collect its allotment of 50 fireflies on its only collecting expedition of the summer.

Led by Lorna McCallister, the Butterfly Pavilion team seeks to understand the lifecycle of the Colorado fireflies and to breed and raise them. As LeCrone discovered in Illinois, fireflies are disappearing from many of their traditional breeding grounds. In fact, a population that once lived in the Reservoir Ridge Natural Area, west of Fort Collins, has not been seen for several years. McCallister and her colleagues hope their work will aid conservation efforts and possibly lead to reintroduction in some areas. They also hope to have them on display when the new, larger Butterfly Pavilion opens in Broomfield in 2027.

The Butterfly Pavilion researchers set up on the boardwalk, then stepped off into the wetland (not allowed for nonresearchers), butterfly nets in hand and headlamps on their foreheads to capture males and females. After collecting, the researchers took the fireflies back to the zoo where they breed and lay eggs. As larvae emerge, the researchers place them in separate containers in varying substrates, temperatures and other conditions to figure out what works best for the insects. They have learned that the larvae seem to prefer eating an apple and snail slushy. Just recently, the first adult firefly emerged from fireflies collected in 2021, the first time that has been done in Colorado they believe.

Out on the boardwalk, another researcher, University of Colorado Ph.D. student Kit Lewers, had set up two GoPro cameras to film the firefly display. Lewers is working in the lab of Orit Peleg, an associate professor in the BioFrontiers Institute at CU. Peleg is trying to learn how fireflies evolved their species-specific flashing patterns. She believes that the flash patterns, which developed over millions of years, might have something to teach us about effective and efficient communication. But it is more than just that.

“At heart, I am fascinated by these creatures and want to understand them,” Peleg said. “They are so beautiful and captivating.”

Lewers used two cameras to create a three-dimensional map of the fireflies that helps Peleg and her team track individual fireflies and their flashes. Peleg and Ph.D. student Owen Martin are crowdsourcing their firefly efforts, with the Colorado Firefly project. On the webpage is a form to gather information about where and when people have seen fireflies in Colorado. For those willing to revisit the location of their sightings, Martin will send two GoPros and a hard drive to film the swarm. Last summer they enlisted about 10 people to film the fireflies, and more have signed up this year.

“There are spots all over Colorado,” Peleg said.

McCallister and the Butterfly Pavilion are also enlisting volunteers to record and share their sightings of fireflies through the Colorado Firefly Watch. On that page, they list several public locations where fireflies can be seen in Colorado. The Western Firefly Project, run by the Natural History Museum of Utah, seeks information about sightings in Utah, New Mexico, Wyoming, Idaho, Nevada and Colorado.

As the researchers and their headlamps departed Fort Collins with fireflies in plastic containers, and the Light Up the Night participants headed back to the parking lot, a peaceful silence settled on the wetland, as the beautiful fireflies floated and flashed silently across the landscape.

After more than three decades’ experience in journalism, science writing, editing, book publishing, corporate communications and video production, William is happy to be freelancing once again about science, skiing or any good story.Twitter: @Allstetter More by William Allstetter