LEWISBURG — The boy shuffled, silently, in the wet grass beneath a maple tree, looking like a little blue ghost in his rain poncho. The sky was deep purple and fading fast.
He held a peanut butter jar in one hand, the cap in the other, and waited, patiently, for nature’s magic show to begin at the Linn Conservancy in Union County. Giggles erupted from out by the corn field, then excited screams by the forest’s edge. Then, in the growing dark beneath that tree, he saw it too, that momentary flash of greenish-yellow, like a fairy, floating through the night.
“Oh my gosh,” Andrés Estrada said, sealing his jar. “I got one.”
The fireflies seemed to outnumber the raindrops on this stormy June night, thousands of them blinking in every direction in the air above the fields.
Researchers say firefly numbers are in decline, globally, however, and there’s a concern that nights like this in Central Pennsylvania and everywhere else, could become rare.
“What’s really become apparent is that we just don’t have enough data,” Sarah Lower, a biology professor at Bucknell University, said at the conservancy. “There’s so much we don’t know about them.”
The decline in recent years has been both anecdotal — people report seeing fewer fireflies than usual — as well as scientific. Richard Joyce, an endangered species conservation biologist with the Oregon-based Xerces Society, said cultural shifts may play a part in the perception. People are outside less and on their phones more.
“We just don’t have a baseline to compare that observation to. It’s not like any of us were keeping great records as kids,” Joyce said.
There’s some nostalgia involved, too. Catching fireflies is as strong a summer tradition as the whir of a Wiffle Ball or drinking from a garden hose. Fireflies are often one of our first positive interactions with nature. They don’t sting or bite when we scoop them from the air. They don’t want to suck our blood. We bring them into our homes, to be little night-lights by the bedside.
There’s even a firefly festival in Pennsylvania in Tionesta, Forest County.
“I’d say, outside of maybe ladybugs and butterflies, fireflies are our favorite insects,” Lower said.
The Xerces Society says there are few long-term studies done on the 2,200 different species of fireflies across the globe, but one conducted in the United States and Canada in 2021 found that 18 of 132 species studied were threatened with extinction. Pennsylvania is home to 30 species, Joyce said, and one of them — photuris pensylvanica — also known as the dot-dash firefly, has been in decline for decades due to habitat loss. The firefly, named after its lighting pattern, lives near tidal watersheds.
“That’s definitely one we’re concerned about,” he said.
Researchers believe a host of issues are at play, including habitat loss through development, global warming, drought, pesticides, and even light pollution, a side effect of overdevelopment. Fireflies, perhaps more than any other animal, need darkness. Their bioluminescent abdomens help them communicate with potential mates. Fireflies have few natural enemies — they’re toxic to most animals — but some even use their light as a mimic, to lure in different firefly species and eat them.
The firefly most ubiquitous to the Philadelphia area, the big dipper (or common) firefly, likes to come out at dusk, Joyce said. It’s less affected by light pollution and more adaptable to development.
“The big dipper appears to be doing OK,” he said.
In New Jersey, where some species may live exclusively in or near the Pine Barrens wetland loss could also be affecting populations. Another species, the Bethany Beach firefly, lives in a very small stretch of the Delaware and Maryland coastlines.
In Lewisburg, the lights from a federal prison lit up the sky a few miles from the conservancy. Before sunset, Lower and a team of her students at Bucknell gave a presentation — Fireflies in the Night — to a group of young campers.
“That’s an egg? That little brown speck? And they grow to be like firefly size?” Estrada said, peering through a magnifying glass.
“Sure do,” Lower replied.
Estrada’s aunt and grandmother joined him for the presentations. Both said lightning bugs — another common name — were “everywhere” during their summers in Delaware County.
Lower grew up in the West, and while there are fireflies there, she recalled being awed by them while visiting her grandmother in Cape Cod. She’s been studying them for 13 years.
“The ones I can really remember are from grad school,” she said.
Most of the presentation by Lower and her team focused on the fun, the many oddities and the unknowns of the firefly world. They’re neither flies, nor bugs, she told them, and they eat other fireflies.
“Fireflies are actually beetles,” she said.
She told the campers about keeping leaf debris and rotten logs in their yards, about cutting back on pesticides and reducing outdoor light.
“They seem to be really associated with organic material in the yards, so leave some of that stuff,” she said.
At dusk, she released the kids with nets and jars, reminding them that kids “on every continent but Antarctica” have done the same.
On a larger scale, the Xerces Society is doing the same through its “Firefly Atlas,” a program aimed at getting the public involved in tracking and conserving “threatened and data-deficient species in North America.” The website iNaturalist.com maps out user-submitted photos, including 336 observations of eight different species in Philadelphia.
“There’s a lot to learn. We’re still drawing out the maps and discovering new species,” Joyce said.
In Lewisburg, Lower went from kid to kid examining what they’d found. Some had squished a firefly or two. Others caught a handful. Lower herself could nab them out of the air with little effort. Under the glow of red lights, she peered into the jar.
“That’s a yellow-bellied firefly,” she said to Estrada.
And Estrada peered in too, his mouth agape.
“This is so cool,” he said. “This is sick.”
