Fireflies and Lightning Bugs

I have always loved watching fireflies and lightning bugs dance in the backyard. They are one of my favorite insects and bring back lots of childhood memories. Even today, I will run outside to watch the first fireflies of the year or to see a particularly good display.

Fireflies and lightning bugs are two different names for the same insect. A study done several years ago found that approximately 40% of people in the U.S. use the two names interchangeably (me!), while approximately 30% only say fireflies, and the remaining 30% only say lightning bugs. To keep things from getting confusing, I’m going to try to stick with “fireflies” throughout this article instead of switching back and forth like I typically do.

Fireflies are familiar insects that light up our night skies and bring back childhood memories for many people. Photo credit: Katja Schulz, cc-by2.0

Fireflies are neither a fly nor a true bug. (No, not all insects are bugs. Yes, there is a category of insects called true bugs.) Fireflies are actually beetles that belong to the Lampyridae family. They can be found on every continent, except for Antarctica, but they prefer more humid, moist areas. It is estimated that there are over 2,000 species of firefly worldwide with approximately 146 species in North America and 15 species in Kentucky. More species are still being discovered.

Fireflies go through complete metamorphosis, just like a butterfly. Eggs are laid in moist ground. After a few weeks, the eggs hatch and a larva emerges. The larva will crawl around in the leaf litter, rotted wood, or the thatch in your yard for 1-2 years depending on the species and location. During this time it is ferocious predator feeding on snails, slugs, and perhaps other invertebrates. Eventually it will pupate. The pupal stage will last a few weeks and is the equivalent of a butterfly in its chrysalis. After the adult firefly emerges, it will only live for about a month. Its primary goal is to find a mate and reproduce so it can start the next cycle of fireflies. Many species of fireflies don’t eat anything as adults, others may be pollinators. Scientists still have a lot to learn about fireflies and even basic questions such as “what do they eat?” aren’t as well understood as one might think they would be.

While the most familiar characteristic of a firefly is its glowing abdomen, not all adult fireflies glow. Many species are diurnal (active during the day) and don’t have the ability to light up as adults. However, all species of fireflies glow when they are larvae. The glow is called bioluminescence and is created through a chemical reaction that takes place within a special organ in the firefly’s abdomen. The reaction produces a very efficient light with virtually no wasted heated energy. In other words, unlike a lightbulb that gets hot when it is turned on, a firefly’s abdomen stays cool. Depending on the species, the light can be yellow, orange, white, blue, or green.

It is believed that the glowing serves different purposes at different stages of the firefly’s life. As a larva, the glow is a warning to potential predators that says, “I’m toxic. Leave me alone if you know what’s good for you.” The larva can even light up inside the egg if it is jiggled. Among adult fireflies that retain the ability to light up, the flashing probably still provides some warning to predators, but its primary purpose is typically to attract mates. Each species has its own flashing pattern. You can actually learn to identify different firefly species by how they flash, just like you can learn to identify birds by their songs.

Although we always associate the fireflies with their glowing abdomens, some species are diurnal and lack the ability to glow as adults. Among the species that retain the ability to glow as adults, each species has a unique flash pattern that allows it to communicate with other members of its species. Photo credit: Ashley Harrigan, cc-by 2.0

Since each species of firefly has its own flashing pattern, it is easy for the males and females of each species to communicate with each other. The males will flash their signal and if a female is interested she’ll flash back. It is thought that the females choose their mates based on the strength, rate, and intensity of the male’s flashing. However, not all fireflies follow the “rules.” The females of at least one genus of fireflies can mimic the signals of other species. They will respond to the males of other species, but when the potential suitor flies close to mate, she eats him instead. The females of this genus may even eat males of their own species, sometimes in the middle of mating.

Fireflies are fascinating creatures and we still have much to learn about them. However, they appear to be decreasing in numbers. Lots of anecdotal evidence supports this. Think about it. How many fireflies do you see now compared to when you were a kid? In many places the answer is “not nearly as many.” The in-depth scientific research to investigate firefly populations has only recently been started but strongly suggests that firefly populations are indeed declining.

While more research needs to be done, there appears to be at least a few general causes for the decline. 1) Fireflies are susceptible to the same pesticides as mosquitoes and many other insect pests. 2) Habitat loss also appears to be a potential factor. When a new development goes into an area, the fireflies that lived there don’t appear to migrate to a new area – they just disappear. That makes logical sense considering that they spend most of their life crawling around on the ground as a larva. Those larva will be killed by the development and the adults have evolved to stay in the general area where they emerged because that’s where the good habitat is located. 3) Light pollution may also play an additional role in firefly population declines because our artificial lights might interfere with their ability to communicate with each other. There may be additional factors influencing firefly populations as well, and as I said, more research is needed.

If you want to help with the research, there is a citizen science project called Firefly Watch that is studying firefly populations across the U.S. All you have to do is observe the fireflies in your backyard and report what you see. Whether you participate in the citizen science project or just sit in awe and enjoy the show, I hope you have the opportunity to enjoy many firefly displays this summer.

This article was part of Shannon’s original Kentucky Pollinators and Backyard Wildlife blog which evolved into the blog for Backyard Ecology.

Backyard Ecology: Exploring Nature in Your Backyard
Nature isn’t just “out there.” It’s all around us, including right outside our doors. Hi, my name is Shannon Trimboli, and I am the host of Backyard Ecology. I live in southcentral Kentucky and am a wildlife biologist, educator, author, beekeeper, and owner of a nursery specializing in plants for pollinators and wildlife conservation. I invite you to join me as we ignite our curiosity and natural wonder, explore our yards and communities, and improve our local pollinator and wildlife habitat. Learn more or subscribe to my email list at

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