Fireflies are in Trouble: What Can Gardeners do to Help?

Fireflies – the magical blinking beetles that mesmerize in the night skies of summer – are in trouble, but there are easy ways to create hospitable places for them in the garden and backyard.

More data needed

“We kept getting all these reports from people that they were seeing so many fewer fireflies,” said Candace Fallon, a senior conservation biologist at Xerces Society for Invertebrate Conservation. “So, we wanted to dig in. Are fireflies declining?”

Candace Fallon examines a firefly in a jar. Photo credit: Xerces Society for Invertebrate Conservation

Fallon and her colleagues in Xerces’ endangered species program began compiling research on fireflies in 2018 but quickly noticed a lack of information about population trends and conservation status. The next year, Xerces partnered with researchers at the International Union for Conservation of Nature (IUCN) Firefly Specialist Group, and the New Mexico BioPark Society to assess the conservation status of 132 firefly species from the U.S. and Canada, about 79 percent of the described firefly species in the region.

In their study published in 2021, the team found that 18 species are threatened with extinction, but she cautions that the number could be much higher.

“Over half the species were data deficient,” Fallon said. “We know enough to say – at least 18 species are at risk of extinction, and there are two other species close to that threshold. About a third seem to be doing OK. But then there’s 50 percent where we don’t know enough. That made it clear we need more data.”

Of the species studied, the Bethany Beach firefly, Photuris bethaniensis, is the most at risk. It is found only on a narrow swath of coastal land along the Atlantic shore of Delaware, Maryland, and Virginia. The IUCN placed the Bethany Beach firefly on its ‘Red List’ as a Critically Endangered Species, and the U.S. Fish and Wildlife Service proposed placing on the Endangered Species List in 2024 – the first firefly to be considered for inclusion. A few states, such as Indiana, Florida, and Maryland, include at-risk fireflies in their state wildlife action plans.

In 2022, Xerces launched Firefly Atlas, a citizen-science project to observe and record firefly species in North America. Precise population data is critical to conservation efforts.

The Ecological Role of Fireflies

Around the world, there are about 2,460 species of Lampyridae, a family of insects within the beetle order Coleoptera, or winged beetles.

Fireflies are predators and scavengers, feeding on soft-bodied invertebrates such as slugs, snails, and worms, “so they can definitely be a gardener’s friend,” Fallon said.

Lampyridae undergo complete metamorphosis with four distinct stages: egg, larva, pupa, and adult. Their life cycles vary depending on species, but they spend most of their time in the larval stage, where they live at or just above the soil surface.

Fireflies spend much of their life cycles underground. Image courtesy of Xerces Society for Invertebrate Conservation.

Moisture is Key Habitat Component

Fireflies are found in a wide range of habitats with one thing in common: moisture. According to Xerces, they have been documented in such places as tidal marshes, desert river canyons, and cypress swamps. In the eastern U.S. and Canada, they may be found in agricultural fields, irrigated lawns, and damp meadows. In the West, they stick to areas with permanent water sources, such as streams, rivers, and lakes.

And while adult fireflies do sometimes visit flowers, Fallon said, they “are not active pollinators so far as we know.”

Because they don’t associate with plants the way bees and butterflies do, she said, planting certain kinds of flowers or plants doesn’t necessarily create habitat for them.

But, she said, “It certainly doesn’t hurt them.”

What Can We Do to Help Fireflies?

Make an oasis. “We don’t know of specific plant species helpful to fireflies,” Fallon said, “but they do need shelter and moisture. They need wild spaces where they can live out their lives, and they need a place to eat. They mostly eat in their larval stage.”

Think about using plants strategically, she said. More vegetation increases moisture and humidity.

Different firefly species prefer different zones for courtship. Some like to stay low to the ground; others prefer the treetops, so give them all some options.

Be a little messy. Fallon suggests leaving rotting logs, leaf litter, brush, and other vegetation in the margins of the yard or garden as a haven for fireflies.

“A big thing we encourage is leaving the leaves in the fall,” Fallon said. “That’s where larvae are hanging out and can overwinter. Anything you do at the soil level could impact fireflies.”

Where feasible, mow as infrequently as possible or move the mower blades to a higher setting.

Mind the lights. Fireflies’ flashing is central to their courtship ritual, and adult fireflies are racing the clock to find mates. If possible, help them out by turning off outdoor lights at night, closing the curtains, and, in places with light pollution, increasing the tree canopy to give fireflies some pockets of darkness.

If turning off the lights isn’t an option, Fallon recommends installing red gel filters on outdoor lights. Consider installing motion detector lights or light shields that direct the light rather than dispersing it over a wide area.

And finally, ditch the herbicides. Chemical treatments for the lawn and garden affect fireflies at every stage of their lifecycle, sometimes killing them outright or changing their behavior, reducing their food sources, and limiting their reproduction. Xerces published this handy guide to dealing with pests without the harmful chemicals.

Why Have Firefly Populations Flown Under the Radar?

Fallon thinks the very nature of fireflies helps explain a lack of awareness about their population health.

“I think fireflies get put into this different category that they’re so magical and people forget that they’re animals. We forget that they’re insects and they can be harmed.” she said. “There's a kind of disconnect that doesn’t exist with bees and butterflies.”

Thanks to advocacy and education about the threats to pollinators by Xerces and other conservation organizations, “everyone knows pollinators are in trouble. I think we’re moving in that direction now with fireflies,” Fallon said

Fireflies are magical!

Main Takeaways:

• While the true scope of the problem is not yet known, it is clear that firefly populations are declining.
• Fireflies are not pollinators, but can be very beneficial for gardeners, feeding on pests such as slugs and snails
• Fireflies will benefit from many of the same measures that protect pollinator species, such as providing an oasis of shelter and moisture by reducing mowing and herbicide use as well as leaving rotting logs and leaf litter in place on the margins of your garden.
• Keep the lights down at night or consider installing red gel filters on outdoor lights or motion detector switches that turn lights off when they are not needed.

You can always email your gardening questions to seeds@rareseeds.com. Put "hort question" in the subject line, and someone on the horticulture team will get back to you.