In recent years, you may have heard a familiar refrain: “I don’t see fireflies like I used to.”
The intermittent yellow glow of fireflies that once illuminated summer evenings can feel like it’s fading.
Whether that’s true, however, is more complicated than it seems.
“Unfortunately, there’s just not really good data on that,” said Chelse Prather, insect ecologist and associate professor at the University of Dayton. “Nobody has been systematically studying the fireflies in Ohio. There’s just not good long-term data on them.”
That doesn’t mean fireflies are free from the pressures affecting insects worldwide. Scientists have documented declines among many insect species globally, and many of the same threats — habitat loss, pesticide use, light pollution and climate change — are also known to affect fireflies. Because firefly larvae develop in soil and leaf litter, the removal of those habitats through intensive landscaping and development is expected to reduce suitable places for them to survive.
The lack of long-term monitoring is one reason projects like the Firefly Atlas, launched in 2022, have become increasingly important. The community science initiative encourages people across North America to document firefly sightings, helping researchers better understand species distributions, phenology and habitat associations.
Although data about Ohio is lacking, residents can still make their yards more hospitable to fireflies by reducing outdoor lighting, leaving leaf litter in place and planting native vegetation.
There are about 120 species of fireflies in North America, roughly 10 of which occur in southwest Ohio. While most produce light as adults, some do not. Many are dark in color, with some bearing orange or yellow markings. Other species, like the little gray firefly, are lighter in appearance.
The glowing adults typically live only a few weeks; fireflies spend most of their lives as larvae in soil and leaf litter — undisturbed dead organic material that has fallen to the ground — before emerging to mate.
In late May through the end of July, larvae pupate into adults, beginning the brief mating season familiar to backyard observers.
Fireflies produce light through a biochemical reaction involving the enzyme luciferase. They use the light either to attract mates or, in some species, to lure prey.
One example is the predaceous Photuris firefly, sometimes called the “femme fatale” firefly because females mimic the flash patterns of other species to lure unsuspecting males close enough to eat.
Female fireflies lay eggs in leaf litter during mating season. The eggs hatch into larvae, which spend months or even years in soil or leaf litter. The larvae resemble tiny armored insects, often compared to miniature trilobites.
They eat snails and other insects also living in the leaf litter. Once they metamorphose into the winged, bioluminescent stage, they’re solely focused on mating.
Some years produce especially large numbers of fireflies. Prather said weather, particularly rainfall and temperature, can have a noticeable effect. Warm, wet springs generally benefit both firefly larvae and the prey they feed on.
But if one yard has fireflies and its neighbor doesn’t, it may be because of how homeowners manage their landscapes.
“Things that homeowners could do to encourage fireflies would be to have certain areas of yards that you do not rake,” Prather said. “If you have no leaf litter, you’re probably not going to have any fireflies. If you’re spraying pesticides or lots of fertilizers, herbicides, those types of chemicals are not necessarily good for them.”
Light pollution is another deterrent. Bright outdoor lighting can drown out the fireflies’ bioluminescence.
“Imagine you’re trying to attract a mate by flashing,” Prather said. “If there are bright lights around, your mate is not going to be able to see you, and so populations are going to go down.”
Prather traveled to see synchronous fireflies at Great Smoky Mountains National Park, a different species than those found in Ohio. The insects flash in unison several times before going dark, creating one of nature’s most remarkable light shows. Even the glow from a cellphone or headlamp can interrupt the display, throwing the insects out of sync.
Fireflies also spend time in grasses before becoming active at night. Frequent mowing can reduce shelter and breeding habitat. While most homeowners aren’t likely to stop mowing altogether, leaving portions of a yard unmowed can help.
Unlike some insects, Prather said fireflies don’t depend on a single native plant species. However, many of the animals their larvae eat do. Planting native vegetation supports those prey species, creating a healthier food web for fireflies. Beyond summer aesthetics, that role is central to the firefly’s place in the ecosystem.
“Their big ecological role would be that larval stage as predators, keeping populations of other organisms in check,” Prather said. “Another would be a food source for other predaceous insects or birds. When you remove them, you’re removing a major predator from the leaf litter ecosystem, and you’re also removing a food source that lots of things depend on.”
The predaceous firefly, for example, is completely dependent on luring in another species of firefly for sustenance. If the common prey species is gone, there is nothing else around to survive on.
“Pretty much all species of insects will have different insects that specialize just on eating them,” Prather said. “Undoubtedly, when you lose just one species, it has a cascading effect on other species in the ecosystem.”
Less-intensive landscape management, as counterintuitive as it sounds, is often one of the best ways to support insect populations. Broad spectrum pesticides, which are often used to kill off hordes of mosquitoes, affect all insects, not just the bad ones.
When Prather moved into the house she lives in now, the landscaping was tightly managed. Chemicals were sprayed. Now, she practices what she preaches: she plants native plants and doesn’t rake all the leaves. Fireflies flash all around her yard. Nearby yards remain noticeably darker.
“The more people that adopt this more hands-off approach to their landscaping, the better it is for native wildlife,” she said. “Not just fireflies, but lots of things.”