On a warm June evening, the first flicker appears above the grass. Then another, then dozens, tiny lanterns drifting through the dark over lawns and meadows across the eastern United States.
For most people, fireflies exist only in those few magic summer weeks. What they do for the rest of the year is a story almost no one knows, and that hidden story turns out to be the reason the lights are slowly going out.
They are not even what their name says
Despite the name, fireflies are not flies at all. They are beetles, and that alone surprises most people.
Like every beetle, they pass through complete metamorphosis: egg, larva, pupa, and adult. The whole cycle can take two to three years or more, and almost all of that time is spent in a stage you never see.
The glittering adults everyone recognizes are barely a footnote in a much longer and stranger biography. The real story is happening somewhere else entirely.
The summer glow is quietly going out
Across North America, that glow is fading. Firefly populations are dropping fast, and one in three species may be at risk of extinction.
A 2024 study analyzing more than 24,000 citizen science surveys found steep declines, tied to climate change, light pollution, and habitat loss.
That same year, the U.S. Fish and Wildlife Service proposed protecting the Bethany Beach firefly of Maryland and Delaware, the first firefly ever put forward for the Endangered Species Act, the same step taken for monarchs.
Something is quietly erasing them, and the reason hides in the one place almost nobody thinks to look.
A language of light that is being drowned out
Fireflies talk to each other almost entirely in light. Males and females flash to find a mate, and some species synchronize their signals across thousands of insects at once.
Artificial light at night, especially blue rich light, easily overwhelms those flashes. Signals meant for twilight and natural darkness simply dissolve into the glow of a single porch lamp.
When the signals are lost, mating fails. And if mating fails for even one summer, there is nothing young waiting in the soil for the next one.
The secret double life hidden under your feet
Here is what those two missing years actually are. Long before a firefly ever lights up your yard, it lives as a larva in the soil and the leaf litter, often for one to two years in the dark.
Down there it is a hunter, tracking snails, slugs, and worms through the damp ground. It spends roughly 34 times longer underground than it ever spends flashing through the summer air.
And it glows even there, buried in the soil, where no human eye is around to see it. Then, one warm evening, it finally climbs out, and the show we love begins.
This is why the loss is so easy to miss. Just like wild bees quietly vanishing from places we never thought to check, the firefly disappears first underground. A dry lawn soaked in pesticide is a graveyard beneath your feet, invisible to everyone standing on it.
What you do in your yard this fall may decide next summer’s show
The strange good news is that the fix is mostly about leaving things alone. Let part of your lawn grow longer, since fireflies shelter in taller grass and wild vegetation.
In the fall, leave some leaf litter where it falls instead of clearing every corner. Those untidy patches of moist soil and slow rotting leaves are not a mess. They are a nursery.
Fireflies and their prey need moisture, so wet springs tend to bring brighter summers, and dry, disturbed ground does the reverse. Researchers tracking insect behavior underground keep finding that what happens in the dark shapes everything we see in the light.
Scientists at the Xerces Society and Tufts University caution that long term data is still thin and the full picture is not complete. But the direction is clear enough. The flicker you saw last June took two years of quiet, invisible work to make. Whether it happens again may depend entirely on what you leave alone.