These days, with our greater appreciation for ecosystems, gardeners tend to have nicer things to say about insects than we did in the past. Maybe not all of them, and not all the time, but there’s more of an attitude of trying to “find the good in everyone.”
But one insect that has never required any effort to appreciate is the firefly. It has always held a special place—admired and even marveled at.
What Are Fireflies, Really?
Depending on where you live, fireflies may be better known as glowworms or lightning bugs. We seem to call them everything except what they actually are: beetles.
And these beetles are known for giving off light. That light is produced through a chemical reaction inside the firefly’s body—a reaction between a special light-emitting compound and an enzyme that produces bioluminescence. When these are combined with other elements, they produce what’s called “cold light”—a very efficient form of light with hardly any heat.
Scientists have studied fireflies for centuries, hoping to understand their energy-efficient light. Their bioluminescence is even more efficient than modern LED lights—brighter and more colorful LEDs exist, but fireflies still lead in efficiency.
Why Do Fireflies Glow?
All fireflies glow at some stage of their lifecycle, but which stages vary by species. In those that light up as adults, the flashes are mostly used for mating. Flying males perform flashing displays hoping to attract a female—who may flash in response if interested. Each species has its own flashing pattern and rhythm.
At least one genus of firefly takes advantage of this. Females mimic the flashes of other species—not to mate, but to lure unsuspecting males and eat them.
A Symbol of Summer—and of Conservation
The magical light of fireflies captures people’s attention and often evokes nostalgia. For many, fireflies are a symbol of childhood summers—chasing them with nets or catching them in jars. That fondness has helped turn them into a “flagship species” for insect conservation, much like monarch butterflies.
And it isn’t just about memories. Fireflies have become rarer in many areas—likely due to habitat loss and other pressures—so people who never saw them as kids are now hoping for a first-time experience.
Synchronous Fireflies and Regional Differences
In much of Eastern North America, the fireflies you see are usually individuals flashing at random. That can still be spectacular—but in a few regions, thousands of fireflies will flash in unison. These synchronous fireflies are a huge attraction at Great Smoky Mountains National Park in Tennessee, where people enter a lottery for tickets in late spring. The star species there is Photinus carolinus.
Southeast Asia is also famous for synchronous fireflies, and in some locations, they appear to flash on and off like they’re controlled by a master switch.
But not all fireflies light up. In many parts of Western North America, fireflies are active during the day and don’t glow at all. Even if they tried, other fireflies wouldn’t see them—so instead, they communicate using pheromones.
A common Eastern North American firefly, Ellychnia corrusca, flies during winter and early spring—during daylight hours—so you likely wouldn’t notice them either. In the UK and much of Europe, the most common firefly species is Lampyris noctiluca, the common glowworm. The adult males barely glow, while the wingless, grub-like adult females emit the visible light. That’s why “glowworm” is the more common name there.
So what you’ll see—or not see—in your yard depends on where you live and which species are present.
Meet the Lampyridae
Fireflies are beetles in the family Lampyridae. There are around 2,400 firefly species across more than 140 genera, found on every continent except Antarctica.
That’s a lot of variation. So while some species have extensive ranges and may be found in different parts of the world, most species are quite localized.
The Firefly Lifecycle
All fireflies undergo complete metamorphosis—egg, larva, pupa, and adult. And the adult stage, the one that gets all the attention, is also the shortest.
While adults only live for two to four weeks, larvae can live for many months—sometimes up to two years. The pupal stage lasts about two weeks, and eggs hatch after around three. Most of a firefly’s life is spent as a grub in the soil or in the litter on top of the soil.
That’s important to keep in mind. The adult you see flashing this summer may have started life a year or two ago and spent all that time in the ground. For every day they spend as an adult, they may have spent two weeks as a larva.
Most adults don’t even feed—perhaps a bit of nectar, but often not even that. Their energy comes from reserves built up during the larval stage. That’s also when they’re voracious predators—eating slugs, snails, earthworms, and other soft-bodied prey.
So if we want more fireflies, we need to support them during their longest, most vulnerable stage—when they live in and around the soil.
Bioluminescence Starts Early
All firefly larvae glow. Many species glow at all four stages—egg, larva, pupa, and adult—but all species glow as larvae. At that stage, the light seems to serve mainly as a warning to predators: “Don’t eat me—you’ll regret it.” And many predators do find them unpalatable.
This defensive bioluminescence came before its use in mating. The mating light display is an evolutionary add-on.
Are Fireflies in Decline?
Probably, yes. Some firefly species are officially endangered, and insect numbers in general are down significantly.
But hard data on firefly populations is surprisingly sparse. Although stories of firefly decline have been around for decades—there was a front-page Wall Street Journal article about it in 1993—they haven’t been a conservation priority, and studies have been limited.
Still, many people—including scientists—say they see fewer fireflies than they used to. It seems very likely that firefly numbers are down.
Threats to Fireflies
The big threats are the same ones that affect many insects: habitat loss and pesticides.
But fireflies face a third challenge—artificial light at night. For millions of years, nighttime was mostly dark, aside from the moon. Now there’s light from houses, stores, cars, streetlamps, and more. That’s a problem for species that rely on flashes of light to find a mate.
Studies have shown that artificial light can interfere with firefly mating displays. Even modest levels of light can have an effect.
What You Can Do in Your Garden
Turn Off the Lights
If you want fireflies, don’t light up your garden at night—especially during their mating season. If you must use lights, keep them dim, point them down, and limit how long they’re on. Use motion detectors or timers if possible.
Trees and shrubs can help block outside light and create darker areas where fireflies can thrive.
Some products are marketed as “firefly-friendly” lighting—especially red lights. One 2022 study did find that red light had less of a negative impact on mating flashes than other colors, but it still had a negative effect. And red light can disturb other wildlife. Turning lights off remains the best choice.
Create the Right Habitat
Since fireflies spend most of their lives in the soil or just above it, the best way to support them is to create good habitat there.
Fortunately, their needs align closely with common gardening goals. Fireflies like moist soil—something many gardeners work to achieve by adding organic matter like compost or mulching with leaves or straw. These practices also reduce compaction and help keep soil cool and moist.
Leaf litter is especially helpful for firefly larvae. “Leave the leaves” campaigns often mention fireflies for this reason. You don’t have to leave all your leaves exactly where they fall—collected leaves can be turned into leaf mold and reapplied later to help retain soil moisture.
Rotting logs and other decaying organic material are also attractive to firefly larvae. A messier, wilder corner of your garden can provide important habitat—not just for fireflies, but for many other beneficial organisms.
Shade improves soil moisture too. Trees and taller plants can help, especially when combined with leaf litter.
And if you mow, do it less often and with the blade set higher. That has been shown to support biodiversity more broadly.
Avoid disturbing the soil. That’s where the larvae live. Minimal disturbance is better.
What About Ponds?
Unless you’re in Japan, you probably don’t need one. Some Asian firefly species have aquatic larvae, but most North American, European, and Australian fireflies do not. Garden ponds with liners won’t provide habitat for them.
Avoid Pesticides
This one’s obvious. Pesticides can kill fireflies or their prey. If you’re using pesticides, you shouldn’t expect to attract fireflies.
If you must do something about mosquitoes, Bti (Bacillus thuringiensis israelensis) appears to be less harmful to fireflies. It doesn’t target beetles and has a more limited range of effects. But it hasn’t been tested on the majority of firefly species—and avoiding pesticides altogether remains the safest bet.
Fireflies in Your Garden
What you end up seeing depends on the species in your area. You may already have fireflies in your garden but never notice them—especially if they don’t fly or glow.
Photinus carolinus isn’t going to travel from the Smoky Mountains to your backyard. But if you provide the right conditions—moist, undisturbed soil, some leaf litter, no lights, and no pesticides—you’ll be doing what you can to support your local fireflies.
A Note on New Zealand Glowworms
New Zealand is also known for glowworms, particularly the ones in the Waitomo Glowworm Caves. But they aren’t fireflies. They’re flies—specifically fungus gnats. That’s the confusing world of common names: fireflies are beetles, and glowworms may not be worms—or even fireflies.
But they put on a great show too.