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This story is part of our series, Wild Pennsylvania. To check out all of the other stories in the series, click here

Catching fireflies, or lightning bugs, as hundreds of tiny lights illuminate a summer night is a fond memory for many children. For some, it is also one of the first times they marvel at nature. While catching fireflies can be fun, according to Bucknell assistant Biology professor Sarah Lower, the practice may hurt the bugs if done wrong. 

To keep fireflies healthy and safe, contrary to popular belief that holes should be cut in the jar to allow air in, the jar should not have any holes, because this can dry out the insects, Lower said. Adding a moist paper towel, coffee filter, or piece of an apple will keep the humidity up, and keep them hydrated. 

One of the most important aspects of keeping fireflies healthy is not keeping them too long. Adult fireflies only live for a couple weeks, and if they have only 10 to 14 days to find a mate, keeping them inside for a couple of days is a significant portion of their life according to Lower. Lower suggests keeping the fireflies for a couple hours, observing them, and releasing them. 

“I love to use catching fireflies as a teaching moment because most folks are really freaked out by bugs,” Lower said. “You are out in the evenings chasing these crunchy bugs that are actually really, really cute, and so you can use this as a springboard to talk about insects, and beneficial insects [with your children],” 

Lourenco Martins (left) and Sarah Lower (right) search for day-active fireflies in North Carolina. Photo provided by Hanh Tran.

Outdoor Lights Hurt Fireflies

Light pollution also impacts fireflies because they light up to attract mates. 

“You can imagine that if there’s a lot of light around, they may not be able to pick out the individual flashes against that really bright ambient light, and so that can actually prevent mating from happening,” Lower said. 

Turning off your lights during summer firefly season (which changes annually, but often starts around late May or June and lasts as long as conditions are wet, potentially into fall) can prevent light pollution from putting a dent in your backyard firefly population.

In Malaysia and Thailand, certain species of fireflies congregate on a single, special tree to flash in unison and attract females. Once a light is put in that shines on that tree, it can no longer be used. The effects of light pollution are just beginning to be studied scientifically. 

Regionally, the health of firefly populations varies due to light pollution. For instance, very few fireflies can be found in downtown Washington D.C., according to Lower. 

In rural areas with less light pollution, generally their health is stronger. Health also varies by species, and the big dipper firefly, one of the most common species on the East Coast, is generally pretty healthy in Pennsylvania, whereas rarer species are often more vulnerable. 

A nocturnal species, the Big Dipper firefly, seen during the day. Photo provided by Hanh Tran.

The Wonder of Natural Discovery

Some of the coolest activities parents and kids can watch for together as they observe fireflies are grooming, flying and flashing in the jar, and possibly allowing the light reaction inside their bodies to be viewed from up-close, according to Lower. 

Another, more gruesome sight involves a certain species of firefly eating another one, if placed in the same jar. Photuris fireflies are femme fatales that begin mimicking the flash responses of their prey species after mating to lure and eat them. Lower said biologists believe they do this to acquire a toxin present in the prey species to sequester into their eggs, and protect them from predators. While fireflies do contain toxins, Lower says they are harmless to humans unless eaten in massive quantities.

Lower has devoted much of her research to the evolution of firefly flash signals, and the underlying genes for signal production and reception. She said that local firefly populations need to be conserved. The Allegheny National Forest, where the Pennsylvania Firefly Festival is held in June, is one of the most spectacular sites to see Pennsylvania’s fireflies.  

“I love the wonder of fireflies,” Lower said. “You go outside, and you can observe them in your backyard and think you know them, and then when you look up closely you start finding out things about predation or all of this really interesting biology. We think we know, but we really don’t. And so there’s so much more to discover.”

Instead of Catching Fireflies, Try Counting Them (and help science while you are at it)