Are Fireflies Disappearing? Why Firefly Numbers Are Falling

What does the evidence show?

For years, the main evidence for firefly decline was anecdotal: people remembered summer nights full of lightning bugs and noticed far fewer as adults. Long-term counts of fireflies are scarce, so scientists have had to piece together a picture from local studies, expert surveys and formal extinction-risk assessments.

The most detailed picture so far comes from North America. In 2021, researchers working with the IUCN published Red List assessments for 132 firefly species from the United States and Canada, about four-fifths of the described species there. They found that:

The large share of Data Deficient species means the true number at risk could be higher. In Europe, the common glow-worm was assessed as Near Threatened in 2024, a sign that even widespread species are under pressure there.

Not every firefly is in trouble. The common eastern firefly, the most familiar lightning bug east of the Rocky Mountains, is listed as Least Concern because it is widespread and adapts well to lawns and parks.

Which fireflies are most at risk?

The species in greatest danger usually have small ranges and specialized habitats. The Bethany Beach firefly (Photuris bethaniensis), found only in wet hollows between coastal dunes along a short stretch of the Delaware shore, is listed as Critically Endangered. The Florida intertidal firefly (Micronaspis floridana), which lives in salt marshes and mangroves in coastal Florida and the Bahamas, is Endangered.

Coastal development, drained wetlands, rising sea levels, groundwater extraction and bright lights from nearby buildings all threaten these species. Because many fireflies spend one to two years as larvae in one small patch of ground, and some have females that cannot fly, they are slow to recolonize places once they disappear.

Threat 1: habitat loss

In a 2020 global survey of firefly experts, habitat loss was ranked the most serious threat. Firefly larvae need damp soil, leaf litter, marsh edges or wetlands where they can hunt snails, slugs and earthworms. Building on meadows, draining wetlands, clearing woodland edges and replacing rough grass with closely mown lawns removes these places.

Threat 2: light pollution

Light pollution was ranked the second most serious threat, a finding that surprised many people. Most fireflies find mates by light, so artificial light at night can drown out their signals. Nearly a quarter of the world’s land surface now has artificially brightened night skies.

Experiments support the concern. In field trials published in 2016, adding artificial lighting cut the flashing activity of a night-active Photuris firefly by about 70 percent and reduced courtship and mating success in the common eastern firefly. A 2014 study found that even low levels of artificial light made it harder for male European glow-worms to find glowing females. Lights affect many other night insects too, as explained in why moths are attracted to light.

Threat 3: pesticides

Pesticide use was ranked third. Firefly larvae live in soil and leaf litter for months or years, where insecticides can kill them directly. Chemicals that kill snails, slugs and earthworms remove the larvae’s food, and herbicides change the plants that shelter them. Lawn treatments, mosquito spraying and farm chemicals can all add to the problem.

Other threats

Experts also identified climate change, poor water quality, invasive species, over-collection and badly managed firefly tourism as threats in some regions. Drought can dry out larval habitat, while sea-level rise threatens coastal species. In places where crowds gather to watch famous displays, trampling and flashlights can harm the very fireflies people come to see.

How scientists and volunteers track fireflies

Because so little long-term data exists, volunteers play a large role. Firefly Watch, started in 2008 by the Museum of Science in Boston and later run by Mass Audubon, asked people to count fireflies in their yards; its data collection has since passed to the Xerces Society. The Xerces Society’s Firefly Atlas, run with the IUCN’s Firefly Specialist Group, maps species and habitats across North America. In Britain, the UK Glow Worm Survey has collected sightings since 1990.

These projects help scientists learn which species are declining and where, and they show which of the Data Deficient species need attention most.

What helps fireflies?

The most useful steps are simple. Turning off or shielding outdoor lights during the firefly season, using warm-colored, downward-pointing lights where light is needed, leaving patches of long grass and leaf litter, keeping damp areas and pond edges, and cutting back on pesticides all make yards and parks friendlier to fireflies. Protecting wetlands and coastal habitats matters most for the rarest species.

Fireflies are not vanishing everywhere, but many species are losing ground. To learn how their light signals work, and why darkness matters so much to them, see why fireflies glow.