Gone in a Flash?

Summertime visitors to Great Smoky Mountains National Park, on the border between North Carolina and Tennessee, can glimpse one of nature’s most magical sights. Right after sunset, tens of thousands of tiny yellow sparks appear and flash on and off in sync. The twinkling lights are produced by a rare species of firefly called Photinus carolinus.

P. carolinus is just one of 2,000 firefly species around the world. Most, but not all, of these species can glow. To do this, they use a process called bioluminescence—the creation of light by chemical reactions inside an organism’s body. This ability allows them to produce a flash (see All Aglow and Flash Patterns).

Scientists study fireflies to understand how the insects put on their dazzling displays and what their signals mean. But as researchers work to learn more about these insects, firefly populations seem to be dwindling. Scientists want to find out what’s causing the number of fireflies to drop and try to halt their decline before some species blink out of existence.

In summer, visitors flock to Great Smoky Mountains National Park, on the border between North Carolina and Tennessee. They come to see one of nature’s most magical sights. Right after sunset, tens of thousands of tiny yellow sparks appear. They flash on and off in sync. The twinkling lights are made by a rare species of firefly called Photinus carolinus.

P. carolinus is just one of 2,000 firefly species around the world. Not all of these species can glow, but most can. To do this, they use bioluminescence. That’s the process of making light by chemical reactions inside a living thing’s body. Fireflies can produce a flash with this light (see All Aglow and Flash Patterns).

Scientists are studying fireflies. They want to understand how the insects put on their flashy displays and what their signals mean. But as researchers work to learn more about these insects, firefly populations seem to be shrinking. Scientists aim to find out why the number of fireflies is dropping. They hope to stop their decline before some species disappear.

Fireflies, or lightning bugs, are a type of beetle. Like many beetles, most fireflies spend the majority of their lives underground as larvae—the immature stage of their life cycle. They emerge in the late spring and early summer as adults to reproduce for several weeks. Many species use their glow during this time to communicate, ward off predators, and attract mates.

If you live in the eastern U.S., you can witness how Photinus pyralis— the most common firefly in North America—uses its glow. Males of the species take flight just after sunset to look for females. They flash their yellow glow in an upward hook pattern that gives the species its common name: Big Dipper firefly. Females on the ground watch this display and respond with their own flashes. Males then fly toward the females, continuing to flash until they mate.

Fireflies are also called lightning bugs. They’re a type of beetle. Like many beetles, most fireflies spend most of their lives underground as larvae. That’s the immature stage of their life cycle. By late spring and early summer, they’re adults. They come out for several weeks to reproduce. During this time, many species use their glow to communicate, keep predators away, and attract mates.

Photinus pyralis is the most common firefly in North America. If you live in the eastern U.S., you can watch how it uses its glow. Males of the species start flying just after sunset. They’re looking for females. They flash their yellow glow in an upward hook pattern. That’s why the species’ common name is Big Dipper firefly. Females on the ground watch this show and answer with their own flashes. Then males fly toward the females. They keep flashing until they mate.

Fireflies’ prominent displays make them an ideal animal to study if you’re interested in how animals communicate, says Sara Lewis, a biologist at Tufts University in Medford, Massachusetts. “We can essentially eavesdrop on their communications,” says Lewis. “Their flashes are like a Morse code—it’s pretty unique.”

Lewis and others have studied the courtship rituals of common species of fireflies like P. pyralis. But scientists know little to nothing about hundreds of other less-studied species. Researchers wonder what secrets these insects will take with them if they become extinct.

Fireflies’ displays are easy to see. That makes them a perfect animal to study if you’re interested in how animals communicate, says Sara Lewis. She’s a biologist at Tufts University in Medford, Massachusetts. “We can essentially eavesdrop on their communications,” says Lewis. “Their flashes are like a Morse code—it’s pretty unique.”

Lewis and others have studied the courtship displays of common species of fireflies like P. pyralis. But hundreds of other species are less studied. Scientists know little to nothing about them. Researchers wonder what secrets these insects have. If they become extinct, they’ll take those secrets with them.

Many researchers and firefly enthusiasts have noticed fewer and fewer fireflies in recent years. But it’s difficult for scientists to say exactly how much firefly populations have declined. There haven’t been many long-term studies of fireflies, and most of the evidence is anecdotal, or based on nonscientific reports without reliable data.

“There’s a lot we still don’t know,” says Sarina Jepsen, director of endangered species at Xerces Society for Invertebrate Conservation in Portland, Oregon. “But there are almost certainly a number of species that are endangered, or at risk of extinction.”

Many researchers and firefly fans have seen fewer and fewer fireflies in recent years. But how much have firefly populations decreased? It’s hard for scientists to say. Not many long-term studies of fireflies have been done. And most of the evidence is anecdotal, or based on informal reports without solid data.

“There’s a lot we still don’t know,” says Sarina Jepsen. She’s the director of endangered species at the Xerces Society for Invertebrate Conservation in Portland, Oregon. “But there are almost certainly a number of species that are endangered, or at risk of extinction.”

Jepsen and others aren’t sure what’s causing fireflies’ numbers to fall, but they have some ideas. One ongoing danger to fireflies is light pollution, which is caused by bright streetlamps and buildings at night. It can confuse fireflies looking for mates by making it hard for the insects to see each other’s flashes.

Insecticides, which are chemicals used to kill unwanted insects, can also kill fireflies and other harmless bugs. In addition, habitat loss affects firefly populations. People clear forests and meadows to make way for roads, houses, and other types of development.

Researchers worry that climate change may affect fireflies too. Climate change has made severe drought more common in certain areas. That’s a problem for firefly larvae, which often live underground for years and require moist soil to survive. In places affected by prolonged dry periods, firefly populations have declined—likely because larvae don’t survive to adulthood.

Jepsen and others aren’t sure why fireflies’ numbers are falling, but they have some ideas. Light pollution is one ongoing danger to fireflies. It’s caused by bright streetlamps and buildings at night. The light makes it hard for the insects to see each other’s flashes. This can confuse fireflies looking for mates.

Insecticides are chemicals used to kill insect pests. But they can also kill fireflies and other harmless bugs. People clear forests and meadows to make way for roads, houses, and other types of development. This habitat loss also affects firefly populations.

Researchers also worry that climate change may affect fireflies. Climate change has made extreme drought more common in some areas. That’s a problem for firefly larvae. They often live underground for years and need damp soil to survive. Firefly populations have decreased in places with long dry periods. That’s probably because larvae don’t survive to adulthood.

Scientists, governments, and everyday citizens are working together to help save these beloved beetles. Some countries in Asia, for example, have set up sanctuaries to protect firefly habitats. People can visit these preserves to see large numbers of the insects lighting up the night. Admission fees then go toward firefly conservation.

Another way to get involved in protecting fireflies is to do so in your own backyard. Anyone living in an area where fireflies are common can try to make the environment around their homes better for the insects. One simple thing to do is to turn off outdoor lights at night, particularly in the summer months when fireflies come out to mate. If you have a garden, avoid using chemicals that might harm fireflies.

Scientists, governments, and everyday people are working on the problem together. They want to help save these beloved beetles. For example, some countries in Asia have set up sanctuaries to protect firefly habitats. At these preserves, visitors can see large numbers of fireflies lighting up the night. Admission fees go toward firefly conservation.

You can also help protect fireflies in your own backyard. If fireflies are common where you live, try to make the area around your home better for them. Turn off outdoor lights at night. This simple step helps, especially in the summer, when fireflies come out to mate. If you have a garden, don’t use chemicals that might harm fireflies.

People of all ages are also joining citizen science groups like Firefly Watch, which is based in Massachusetts. Once a week during the summer months, Firefly Watch volunteers around the country count the number of flashing beetles they see in their backyards during one 10-second time period. Volunteers report their findings online, along with other observations, like the time and temperature. Researchers can then use the data to get a better sense of firefly distribution.

Why put in the effort to help fireflies? “It’s important to protect all species and the diversity of life on Earth,” says Jepsen. But fireflies’ glow makes them particularly magical. “They inspire people who aren’t typically interested in conservation,” she adds.

People of all ages are also joining citizen science groups like Firefly Watch. This group is based in Massachusetts, with volunteers around the country. The volunteers collect data in their backyards once a week during the summer. They count the number of fireflies they see during one 10-second time period. Volunteers report their findings online, along with other information, like the time and temperature. This data helps researchers to see how fireflies are spread out.

Why work to help fireflies? “It’s important to protect all species and the diversity of life on Earth,” says Jepsen. But fireflies’ glow makes them extra magical. “They inspire people who aren’t typically interested in conservation,” she adds.