Just past 9 p.m., near the Lakefill’s edge, small points of yellow light hover and blink above the damp grass. The firefly flashes continue, steady and silent, long after most people have gone home.
It’s a sight more common this July than in previous years, and one that University of Illinois entomology professor May Berenbaum said is worth paying attention to.
Fireflies can function as an environmental barometer, she explained. If they are flashing, something in the ecosystem is working. This summer’s abundance might be rooted in something straightforward: rainfall.
“They thrive in moist environments,” Berenbaum said. “Many of them feed on slugs and snails, which also do well when it’s wet. Some species are even semi-aquatic.”
In July 2025, Evanston received about 4.5 inches of precipitation, which was about two inches above the average, according to the Old Farmer’s Almanac July 2025 forecast summary. That water may have created ideal conditions for the fireflies currently winking around at Northwestern.
Richard Joyce, a researcher at Tufts University’s Firefly Watch project, said fluctuations in firefly numbers are often natural.
“Insect populations aren’t consistent year to year,” he said. “Some firefly species are incredibly adaptable. But they still face persistent stressors – pesticides, habitat loss and light pollution, especially in urban and suburban areas.”
Northwestern’s campus, though, may offer the insects a pocket of more favorable terrain. Emily Paschall of California, a student attending the Medill-Northwestern Journalism Institute, said she had never seen fireflies in real life before coming to campus.
“I’d only seen them in kids’ shows,” Paschall said. “But they were everywhere here, and they would even fly up really close to people.”
Firefly activity has been especially noticeable around areas like the Lakefill and South Campus, where low lighting and water-retaining soil create ideal conditions for their mating displays, which are known to be disrupted by artificial light.
That communication, Berenbaum explained, is tightly coded. Each species has its own flash pattern, in which males signal in flight and females respond. Interruption to this process can prevent successful mating.
“My guess is that campuses avoid some of the landscaping practices that make other urban areas harder for fireflies to survive,” Berenbaum said. “They’re not spraying pesticides as aggressively, and they tend to maintain green space.”
Evanston residents are also working to preserve insect-friendly spaces. Natural Habitat Evanston, a Climate Action Evanston program, encourages residents to plant native species, reduce lawn mowing and cut back on artificial lighting.
“We run a program called the Pollinator Pledge,” said steering committee member Tim Sonder (Medill ’83). “We ask people to pledge to do things that improve habitat such as reduce lighting, don’t use pesticides, leave the leaves, reduce mowing and turf.”
The program’s signage system also helps raise awareness. The small yard signs often staked near native gardens or low-mowed lawns, let passersby know that the area supports pollinators and other insects.
“As you walk around Evanston, you’ll see quite a few of these Pollinator Pledge signs that I designed,” Sonder said. “The idea is to change the culture, to make it more acceptable and understandable and something that people want to do.”
Even so, Berenbaum warned that the current uptick in firefly activity doesn’t guarantee long-term health.
“Insects respond quickly to change,” Berenbaum said. “Populations can drop just as fast as they appear.”
That rapid responsiveness is exactly what makes fireflies important to watch. Each flashing insect, she said, is a glimpse into an ecosystem holding together, one flicker at a time.
