How a Soggy Spring and Hot Summer Nights Made 2025 an ‘Exceptional' Year for Fireflies

New York Times

6 hours ago

'Every summer without fail,' said Adam Young, recalling summer nights chasing fireflies as a child in Iowa, 'I remember running barefoot in the grass at dusk, listening to the crickets and cicadas, chasing fireflies until it got too dark to see,'
Mr. Young, who would later rise to fame as the musician behind the band Owl City and its song 'Fireflies,' still recalls those summers fondly.
'You learned to keep your mouth shut,' he said. 'There were thousands of them — you'd ride your bike around and they'd hit you in the face.'
This summer, that childhood magic seems to have made a comeback. From city parks to suburban backyards, fireflies have been lighting up the evening sky across the northeastern United States in greater numbers than in recent years — making it feel as if the opening lines of Mr. Young's debut hit were the literal truth: 'You would not believe your eyes, if 10 million fireflies lit up the world as I fell asleep.'
And the reason? The weather.
Fireflies thrive in warm, humid conditions.
Fireflies, or Lampyridae, are not flies or worms, but beetles, and ancient ones at that.
'They have been around for millions of years before humans evolved,' said Jessica Ware, a curator and the division chair of Invertebrate Zoology at the American Museum of Natural History in New York.
There are more than 2,200 known species worldwide, with 165 documented in the United States and Canada, according to the Xerces Society, which works to protect invertebrates and their habitats. New species are still being discovered.
Fireflies are coldblooded insects, meaning their body temperatures are regulated by their environment. They thrive in warm, humid conditions — just the sort of setting Mr. Young recalls from his Iowa childhood.
'They produce an enzyme, luciferase, that interacts with a substance called luciferin, with oxygen, magnesium and a little energy to produce light,' said Sarah Lower, an assistant professor of biology at Bucknell University.
The reaction that produces that magical-seeming light is more efficient in warmer air, which explains fireflies' increased activity during hot, muggy summers.
Adult fireflies live only briefly. Their lives underground, however, span much longer.
'Fireflies spend up to two years in the larval stage before they emerge as adults,' said Professor Lower. But as adults, most only live about two weeks, she said.
A couple of particularly soggy spring seasons in recent years might have given firefly larvae a boost, experts said.
New York City received 16.64 inches of rainfall in spring 2024 and 15.35 inches in spring 2025 — both well above the seasonal average of 12.34 inches, according to the National Oceanic and Atmospheric Administration. Meanwhile, Philadelphia got 13.07 inches in 2024 and 14.41 inches in 2025, also higher than its spring average, which is 10.77 inches.
Zack Taylor, the branch chief at NOAA's Weather Prediction Center, noted that unusually warm summer nights this year may be another contributing factor. He explained that clouds, high humidity and light winds can trap heat near the earth's surface, keeping nighttime temperatures elevated. Because fireflies thrive on warm and humid conditions, these above-average overnight temperatures also could be fueling the noticeable increase.
Overnight lows in Central Park are among the warmest on record, he said, and the same is true in Philadelphia. In fact, he added, since June 1, several locations east of the Mississippi River are experiencing their warmest average lows on record: Raleigh, Charlotte, and Wilmington in North Carolina; Huntington, W.Va; and Kennedy Airport in New York.
Gabriel Willow, a naturalist who leads nocturnal ecology tours in Central Park and Prospect Park, has also noticed the uptick.
'It's an exceptional year for fireflies,' he said. 'Last spring and summer, and this year as well, were both wetter than average, so that's helped the fireflies survive and thrive.'
This is a bright year, but many species are at risk.
Candace Fallon, a biologist at the Xerces Society, said it was uplifting to hear so many reports of larger firefly populations, but it was difficult to draw any conclusions from a single season of data.
'Because firefly populations can bounce up and down each year, depending on local conditions,' she said, 'we really need long-term data sets to understand how fireflies are doing over the long term.'
The Xerces Society maintains a community science program called Firefly Atlas, which collects data on firefly distribution to produce rough estimates of abundance, habitat associations, phenology and threats. But Ms. Fallon said monitoring at established sites was still in its infancy in the United States.
'We lack base line data from prior decades to authoritatively speak to how populations are faring compared to the past,' she said. 'That said, anecdotal reports, documented threats to fireflies, local extirpations, and research on population trends of other insect groups all suggest that fireflies are declining.'
At least 18 of the estimated 170 North American species are considered at risk of extinction, according an assessment the Firefly Atlas completed with the International Union for Conservation of Nature Firefly Specialist Group.
Habitat loss, pesticide use, light pollution and climate change are the primary drivers.
'They need dark night skies as they flash a species-specific pattern of light to communicate and find a mate,' Dr. Ware said. 'Light pollution makes it hard for the species to find their mates which means fewer mating successes and smaller population the next year.'
Mr. Willow said that the most abundant species in New York — Photinus pyralis, or the 'big dipper firefly' — is more resilient to light pollution than others.
'It generally is out for a couple of hours around sunset at dusk looking for a mate,' he said. 'Since it comes out and displays when it's lighter out relative to some other fireflies that prefer darkness, it's less sensitive to light pollution.'
Counterintuitively, that means cities might offer safer conditions for fireflies than rural or suburban areas, as long as green spaces exist.
'Cities don't tend to have widespread insecticide use aside from spraying for mosquitoes,' Mr. Willow said. 'That can make them unexpectedly hospitable environments for insects like fireflies — especially where there's parkland, unmowed grasses, native wildflowers and trees.'
Here's how to keep fireflies around for the future.
So what can be done to keep the magic glowing for future summers?
'Lights out for lightning bugs,' said Professor Lower. 'Turn your outside lights off during the summer.' She also recommends leaving your leaves to decompose in the soil in the fall and not mowing at least part of your yard — 'devote it to fireflies,' she said. Moist, organic soil is critical. Creating a dark part of your garden by planting taller trees and shrubs can also help fireflies thrive, she added.
For those tempted to relive childhood summer nights by catching fireflies in jars, there's a responsible way to do it.
'We recommend catch and release,' Professor Lower said. Most North American species only have a few nights of adulthood, 'so capturing them in a jar can prevent them from finding a mate,' she said.
If you do capture them in a jar, she recommends skipping the holes.
'Fireflies dry out rapidly, and holes make that worse,' she said. 'Put them in an enclosed jar with a piece of damp paper towel or a piece of apple.'
If you're going out to spot fireflies, Mr. Willow recommends seeking out grassy areas with scattered trees.
'Strawberry Fields in Central Park, the Long Meadow in Prospect Park, really any grassy areas in city parks and even patches of grass in backyards or abandoned lots,' he said. He added the best time is around sunset and two to three hours afterward.
'The fireflies start flashing earlier in shady areas under trees where it's darker, and then later in open areas when the light levels drop.'