Fireflies are disappearing, but we may not know enough about these insects to save them

Firefly Getty Images/Jeremy_Hogan
Firefly Getty Images/Jeremy_Hogan

It's not easy counting fireflies. Across North America, there are an estimated 170 fireflies species, which are technically beetles in the order Coleoptera, but inventorying them is a challenge. While there have been some efforts to conduct a firefly census from nonprofit organizations like the Xerces Society for Invertebrate Conservation and various academic research centers, still proving how rapidly the firefly population has declined in recent decades has been a challenge.

While fireflies, or lightning bugs as they are commonly known, are considered to be a staple in the Northeast, it's also the region where many firefly species are most vulnerable to going extinct. Currently, there are no firefly species that are officially protected under the Endangered Species Act, though, assuming they need saving, there is a tiny glimmer of hope that might change and threats to fireflies would be recognized.

Some firefly species like the Bethany Beach firefly (Photuris bethaniensis) have gained recent awareness through a proposed emergency petition to allow this firefly species to be covered under the federal Endangered Species Act.

In recent decades, the Bethany Beach fireflies, known for their rapid, successive green flashes, started disappearing alongside the threatened freshwater wetlands area of Delaware and Maryland. As conservationists realized fireflies were under threat, public awareness grew for these firefly species that live in the habitat as well.

"It's essential for all of us to work to conserve fireflies," said Dr. Casey Sclar, Ph.D., the H.O. Smith endowed director at the Arboretum at Pennsylvania State University and adjunct professor of entomology at Penn State University.

"We are all enamored with fireflies," Sclar said, "But we know so very little about them."

Signal from the noise

Of course, their flashing is their most familiar aspect, which can vary significantly between firefly species. But generally, fireflies blink and flash to attract mates. These kinds of fireflies are traditionally nocturnal maters. In the dusk or evening hours when you see a firefly flashing it's typically an airborne male in search of a female mate who can be found seated on a leaf or close to the ground where they hide or camouflage themselves.

Female fireflies will observe the males' flashing patterns until the two start a courtship dance. Females, who are capable of flying but don't typically fly as much compared with the male during the mating season, may respond by flashing back in a distinctive female flashing pattern.

It may be hard for the untrained eye to easily visually distinguish between the majority of male and female fireflies (although there are always species-specific exceptions.) Depending on the firefly species, some females may exhibit unique, distinctive flashing patterns. For other female fireflies, they may flash in a specific area of its abdomen that differs from males.

In a single night, both male and female fireflies may mate with many partners. Yes, you can think of every firefly display as a kind of beetle orgy. A female firefly has the ability to lay up to 500 eggs, but without more research, we're unsure how many eggs survive the journey from egg to larvae.

Within the genus of flashing or blinking fireflies (since there are also fireflies that do not flash during mating), there are clear species-specific variations to firefly blinking or flashing whether its differences in color, hue, timing of the flash or another difference. Fireflies pull off this light show using bioluminescence, a specially-evolved chemical reaction that occurs inside their "lanterns" (yes, that's the technical term) using a molecule called luciferase. They can also excrete toxins called lucibufagins, that makes them taste unappealing to other animals like toads and other firefly predators.

There has been limited research on bioluminescence and luciferase, which is sometimes extracted for medical science. While it is generally not possible or sustainable to have huge firefly lab populations (scientists would need access to thousands of lab fireflies in order to extract only a small amount of the chemical), at the same time there are still some specific lessons related to human health we can learn from fireflies.

Bioluminescence imaging, that mimics the fireflies glow, is frequently used in scientific research for mapping diseases, such as cancer or other health conditions. According to a 2022 study in the journal Angewandte Chemie International Edition, this breakthrough could potentially increase use of a bioluminescent reaction, thus reducing the costs of light bioluminescence imaging in a research setting. The study's authors believe this research finding is significant because the next step would be to monitor human diseases that lead to altered oxygen metabolism, including cancer, cardiovascular disease, diabetes and more. Ultimately, more bioluminescence research is needed — and we could be driving the creatures that could help us with such medical breakthroughs to extinction.


Yet, there are still many fundamental open questions about fireflies. Sclar notes scientists don't really know what happens during optimal breeding periods and firefly larval development. Female fireflies lay their eggs in the ground, favoring moist soil and areas near bodies of water. During this time period, larvae and juvenile fireflies alike rely on ground habitat where they can develop and grow undisturbed. While developing, these young fireflies are dedicated carnivores, consuming a range of small bugs and insects, plus the occasional snails, slugs and worms. They are known to scavenge carcasses as well.

Though fireflies can spend approximately 10 months growing and developing in the soil, "We don't really know when to reliably expect them each year." Sclar said."Clearly there are basic effects like land development and type of vegetation choice and the effect on their development [and] the amount of seasonal rainfall and the effect on their development [are among the range of factors]" he added.

In short, anything can go wrong even under the best conditions during the firefly reproductive cycle. But over the past three decades, Sclar said, when looking at the striking changes in land distribution maps, it's not just speculation that habitat loss has had an impact on the firefly population in states like Pennsylvania and elsewhere throughout the Northeast corridor.

"It's difficult to say we counted X number of firefly adults in the 1980s or 1950s, but when you look at the land use development patterns and it's just a timelapse series that you can watch how quickly things have changed," Sclar noted, referring to not only Pennsylvania, but other cities and states that have gone through similar transformations.

"It is stunning to see how that land use pattern has changed from being forest or an agricultural habitat to being edge habitat to housing," he said. "Now we have urban areas with concrete and the increase of the impervious surfaces. It is an easy correlation to look at the amount of growth and firefly population decline."

Clearly, fireflies have not only seen significant decline not only throughout Pennsylvania, but many Northeast states, and elsewhere in the country.

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The Texan firefly in danger of dying out

According to Firefly Conservation & Research, a Texas-based nonprofit organization, the Texan firefly season could extend from as early as April all the way through October, something that is unique to warm weather states. In contrast in the Northeast, firefly season typically extends from the summer months of June or July through August.

Knowing when and how to look for fireflies is essential, said Ben Pfeiffer, a recognized firefly researcher and Texas-certified master naturalist. "There are dozens of under-researched firefly species," he said, noting that he believes there is a significant undercount of Texan fireflies due to data deficiency.

One of the most vulnerable firefly species in the state is the sky island firefly (Photuris flavicollis). Like its other vulnerable firefly cousins throughout the state, the sky island firefly has been disappearing due to oil and gas development in the West Texas area, light pollution, drought and other factors. Scientists report that information about fireflies is oftentimes "data deficient" which is why so many local, state and nationwide data collection initiatives, including Firefly Atlas or Firefly Watch are invaluable to collectively report firefly sightings and develop other helpful data points.

Fireflies bred in the lab

In other geographical regions of the United States, already low firefly populations have disappeared even more dramatically. Out in Colorado — hardly a place known for a significant firefly population to begin with — Butterfly Pavilion recently announced they had successfully bred three Colorado firefly species in their lab through their Firefly Life Cycle Project that started in 2017.

According to Lorna McCallister, the target species manager at Butterfly Pavilion, while the actual number of lab-bred fireflies in this initiative may seem miniscule, it's a feat that is surprisingly uncommon in labs. The organization's goal is to grow its lab firefly population to a much higher number. Starting from scratch meant there was a lot of trial and error when it came to the firefly egg and larvae stages, she said.

Ultimately, McCallister noted that the nonprofit organization's goal is to bolster firefly wildlife populations by rearing vulnerable firefly larvae in a lab and getting them to adulthood. Releasing these fireflies could potentially create or restore new Colorado firefly populations out in the wild, she said.

The organization has several other firefly-specific initiatives, including educational community events and data collection events, McAllister said. While many native Coloradans might be surprised to know that there is a small but established wild native firefly population, the fact is dozens of Colorado fireflies (both glowing and non-glowing species) are present throughout the state, McAllister said.

The impact of light pollution

Light pollution from artificial lights is one major reason fireflies seem to be experiencing such a drastic population decline, as clearly flashing is essential to fireflight mating success and reproduction. Fireflies seem to gravitate to artificial white LED lights, but the overwhelming brightness can discourage males from flashing, leading to diminished mating opportunities.

Homeowners can make simple fixes in their backyards, farms and businesses. According to Sclar, it's best to avoid using standard broadscale white lights in one's backyard — consider red-lights or green lights instead. Non-white colors are thought to be less attractive to fireflies, not to mention other insects who are confused by the light.

Sclar says light pollution is definitely a factor when academics look to firefly population decline. "If there is anything that we can do or to stop doing, as it relates to having a negative impact on the firefly population, I am interested in knowing what those things are," he said.

Firefly tourism: Too much of a good thing? 

Citizen firefly enthusiasts are a key component for knowing when fireflies are scarce or abundant, Sclar said. Luckily, many great community initiatives and data collection collectives exist, according to Sclar and others, that help improve public and academic knowledge of fireflies. Enthusiastic citizen firefly advocates have helped scientists and academics access information relating to changing firefly mating seasons and local firefly population estimates.

"Eco-tourism events dedicated to fireflies are great," Sclar said. "Particularly when community or citizen scientist events emphasize minimal interventions when it comes to firefly populations."

In fact, that's one of the principles, nonprofit organizations like Butterfly Pavilion are all about. The organization aims to educate and connect regular people to the fireflies in the community. Citizen firefly enthusiasts who are encouraged to fill out detailed data sheets to share with Butterfly Pavilion and other partner organizations.

While firefly tourism and citizen firefly advocacy is generally positive, it can sometimes come at the expense of the fireflies themselves. These insects tend to want to left alone and large scale night walking tours that emphasize handling fireflies or disturbing their breeding grounds, intentionally or not, may have a negative impact on their population.

Some experts disagree whether you should you catch fireflies and put them in a glass jar. Some organizations like Firefly Conservation & Research believe that with some well-established parameters, catching and releasing fireflies shouldn't be a big issue. Others disagree and say that adults and or adults and children should avoid any catch and release community activities when it comes to fireflies. Standard best practices are to observe fireflies from a distance and to be mindful of fireflies when walking in firefly-rich forest or wetlands areas — try not to disturb potential firefly breeding grounds whenever possible.