Why fireflies are everywhere this summer

As the early-2000s bop goes, you would not believe your eyes, if 10 million fireflies lit up the world as I fell asleep. While 10 million may not be the exact number of the summer staple lighting up the sky, several states across the country are reporting increased sightings of fireflies–or lightning bugs. 

“The whole forest was blinking,” Kimberly Mackowski of West Allis, Wisconsin told Wisconsin Public Radio. “It’s like someone put blinking lights on, right at the forest entrance.” 

Parts of Pennsylvania, Illinois, and even primarily urban areas like Washington DC and New York City have experienced an uptick in this summertime natural wonder. Their yellow, green, or red glow when paired with chirping crickets or cicadas buzzing signals hot and hazy summer days. While there may be as many as 2,400 species of firefly on Earth, these insects have faced years of decline due to increased light pollution, habitat loss, pesticide use, and climate change.

The insects are still in trouble, but this summer’s increased reports are a welcome sight to scientists and citizen scientists alike.

Fun with fireflies

Despite their name, fireflies are not flies at all. They are a type of beetle in the family Lampyridae. Their signature flashes are signals emitted to attract mates.

“Those flashing sequences that seem random to us are full of species-specific communication,” entomologist Emma Grace Crumbley tells Popular Science.

A 2024 study found that the glow of the Lampyridae family may have evolved due to a particularly stressful situation. A key ingredient in firefly bioluminescence called luciferin has antioxidant properties and firefly ancestors evolved and diversified it when atmospheric oxygen levels rose during the Toarcian Oceanic Anoxic Event. This mass extinction event roughly 183 million years ago during the Early Jurassic caused oxygen levels to plummet in the world’s oceans. Since surviving that and a few other periods of mass death on Earth, this family of luminescent beetles has developed the flashy mating signals that we see today.

[ Related: Spiders may be hacking firefly signals to trap dinner. ]

“Male fireflies fly around looking for mates while females remain close to the ground and signal in tall grass – those flying fireflies you catch are almost all males,” explains Crumbley.

Fireflies thrive in sheltered areas that will protect their eggs as they develop, but will also conceal themselves during the day

“If your location (your lawn, backyard, or neighborhood) lacks long grass, ground cover plants, or leaf litter, then fireflies are less likely to establish,” says Crumbley. 

Why are some places seeing more fireflies this summer?

There are several reasons why some places might be seeing more of these glowy beetles this summer. The first is wet weather. Several parts of the United States saw decent amounts of rainfall this spring. Fireflies seek out moist soil to lay their eggs and take shelter and thrive in covered foliage.

“If your region receives consistent, moderate rainfall and experiences warm, humid temperatures throughout the summer, it is well-equipped to foster firefly populations,” says Crumbley. “Areas that are too cold, too dry, or too exposed do not harbor fireflies as easily.” 

The second reason is a potential lifecycle gap. Fireflies operate on a two-year gap between generations, with adult fireflies living about one to four weeks depending on the species and environmental conditions. This means there could be a fluctuating prevalence year after year, and this year might be a banner year in some places.

“It could be that you live in a warm, wet part of the US with plenty of forest or field space for fireflies to thrive in, yet you still aren’t seeing as many fireflies this year,” explains Crumbley.
“Even if the environmental conditions are correct, the firefly lifecycle may be the reason you don’t see as many flashes this year.” 

Another reason has to do with the more than 150 unique fireflies that live in the US. Their ranges all vary from species to species, with the East Coast seeing more Photinus pyralis, or common eastern firefly.

“It may be that your area is only home to a select few species of fireflies, making it appear that you have fewer than someone a few states over,” says Crumbley. “Synchronous fireflies, for example, are only found in Appalachia (prominently in the mountains of Tennessee). If you were to compare the synchronous fireflies you see outside of this range compared to the annual numbers tracked throughout the Great Smoky Mountains, it may seem like you experience fewer fireflies than usual, when in fact, these fireflies are not found in your area at all. 

How to promote fireflies around you

Even with these synchronous events and reported sightings, fireflies are still in trouble and at serious risk of extinction. 

“It’s unfortunate, but it may simply be that the threats to fireflies (habitat loss, light pollution, pesticide use, and climate change) are the reason for their decline or abandonment in your area,” says Crumbley. “It’s not too late to promote firefly populations local to your area, and there are several things you can do to encourage fireflies to reestablish.”

[ Related: The land of lost fireflies is probably a humble New Jersey bog. ]

Building a firefly habitat in your own backyard or asking community leaders to build some in public greenspace is one way to start. According to Crumbley, Firefly.org, offers numerous resources for how to start. A firefly habitat can be as simple as leaving behind a small pile of leaves after fall cleanups, planting more native plants, or allowing the grass to grow just a little taller. Responsible pest management options, such as reducing pesticide use or finding more environmentally friendly ways to control unwanted bugs like mosquitoes or ticks can also help.

Fireflies need dark skies to find their mates, so tackling light pollution is another solution. 

“Each firefly species has a unique pattern and rhythm, but light pollution can disorient fireflies and make it difficult for males and females to find one another,” says Crumbley. “Reducing lights around your yard as much as possible at night can help restore darkness to your outdoor spaces and assist fireflies in their search for mates.”

Less light pollution can only help fireflies, but other species like moths or even sea turtles, if you live near the beach. 

 

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