Decoding Fireflies’ Smelly Signals And Blinking Butts

IRA FLATOW: This is Science Friday. I’m Ira Flatow. One of my favorite sites of summer is fireflies. You know, their magical, blinking lights serving as tiny beacons in the warm, dark night. Who could resist catching one, right? Because their light comes from bodily chemicals, the special way that fireflies light up has long been used as a research tool in medicine, driving scientists to better illuminate the inner workings of the beetle. And as such, researchers have recently discovered that fireflies’ glowing lanterns are just one of the ways they communicate.

Joining me now to talk about the latest firefly science are my guests, Dr. Sarah Lower, Associate Professor of Biology at Bucknell University, based in Lewisburg, Pennsylvania. Dr. Stephen Miller, Professor of Biochemistry and Molecular Biotechnology at the University of Mass Chan Medical School, based in Worcester, Massachusetts. Welcome to Science Friday.

SARAH LOWER: Thank you so much.

STEPHEN MILLER: Thank you

IRA FLATOW: Sarah, I wanted to start with an overview of the firefly population. I’ve seen some reports that fireflies are making a comeback. I didn’t even know they were in danger.

SARAH LOWER: So what most people don’t realize is that there are more than 2000 species of fireflies. I think we’re up to 2,628, and each of these firefly species has its own habitat requirements. So there are some species that are quite abundant. I’m thinking about the common Eastern Firefly, here on the eastern part of the United States. This one is usually the one that people see when they are out on their porch in the summertime. They’re active around sunset and they can be quite abundant.

IRA FLATOW: Right.

SARAH LOWER: But there are other species that are much more rare, and those are the ones that we are particularly concerned about.

IRA FLATOW: Now, what determines how good a quote unquote “crop of fireflies” we have in any one year? Are there environmental issues?

SARAH LOWER: That’s a great question. Based on some work that we’ve done, using data from folks such as yourself who log their firefly sightings in an app, we were able to identify that weather, in both the current year as well as in previous years, is really important in determining firefly abundance. So fireflies spend one to two years in the larval stage. And so if the factors a year ago– if the weather a year ago was not very great, they can actually delay their pupation to become an adult.

IRA FLATOW: What if it’s really rainy out? Does that affect the population?

SARAH LOWER: Some of the reports that we’ve been hearing this year from people, especially in the mid-Atlantic area, have been that fireflies have been super abundant this year and some of that could be linked to rain. So in other parts of the country where there’s been drought, there haven’t been too many fireflies observed. But we’ve been hearing anecdotes from people in New York, in Pennsylvania, that there are just bumper crops of fireflies this year.

IRA FLATOW: Yeah Well, what about fireflies in urban areas? Do they live a different life, have a different population dynamic?

SARAH LOWER: So I just got done with the International Firefly Symposium in Tlaxcala, Mexico. And–

IRA FLATOW: There is such a thing?

SARAH LOWER: There is. And anyone who is a firefly enthusiast, scientist, educator, storyteller, artist is welcome to come and contribute. One of the things that came out of that conference is that there are firefly populations in urban areas. I myself have collected fireflies in DuPont Circle, in Washington, DC. So this is a highly populated area with lots of traffic and hard surfaces and light pollution, all of which are things that we don’t think of as firefly friendly.

Research from this conference suggests that, in other places in the world where they have these urban firefly populations, they’re actually remnants of populations from a long time ago, and that the area that they are in is the remnant forest that used to be there. And so it’s really important to conserve those populations because they’re going to be really hard to get back if they blink out.

IRA FLATOW: Wow, that is very interesting. You’ve segued nicely into my next topic, the blinking part. Steve, as I mentioned at the top, fireflies’ glowing lanterns have a lot of medical research applications. But before we get into that, can you explain the chemistry, the chemical reaction, the cold light, so to speak, that fireflies light up with?

STEPHEN MILLER: Yeah, so fireflies are beetles that chemically emit light when an enzyme, they produce, firefly luciferase, acts upon a small molecule they make called D-luciferin, to produce an excited state molecule called oxyluciferin. So here, they’re using the chemical energy of oxygen to access this excited state. And when that molecule drops down to the ground state, you get the emission of a photon of light. And that’s the yellow-green light you see from the firefly.

IRA FLATOW: So why fireflies glow up. But do other insects or animals have this ability also, Steve?

STEPHEN MILLER: Yeah. So there are many other bioluminescent fireflies, as Sarah mentioned. There are other beetles that are capable of bioluminescence. So the enzyme, firefly luciferase, is thought to have evolved from a family of proteins that operate on fatty acids that are present in all insects. And so we were, in particular, were studying fruit flies. And we asked, could fruit flies be capable of bioluminescence? And we asked this because the fruit fly enzyme that operates on fatty acids is 40% identical to firefly luciferase.

But mercifully, fruit flies do not glow in the dark.

IRA FLATOW: [LAUGHS]

STEPHEN MILLER: They do not make D-luciferin. And if you take that enzyme from the fruit fly and you give it D-luciferin, nothing happens. But in our lab, we make many synthetic luciferin analogs to change the properties of light emission. And we found if we take the fruit fly enzyme and we treat it with one of the molecules we made in the lab, that it would glow. It would emit light. So no change to the enzyme. We just give it a new substrate and we see light emission.

IRA FLATOW: That must have been spooky.

STEPHEN MILLER: It was spooky, but it was cool, because we’re also trying to see whether this could apply beyond insects into, say, mammals, like mice or even humans. Because we have those same types of enzymes in our body. They’re not as closely related to firefly luciferase. But in principle, if you could make a molecule that was a substrate for one of those enzymes, we might be capable of light emission as well.

IRA FLATOW: I’m just letting that sink in for a second. Where– would you use it internally as a diagnostic, or how would you use it?

STEPHEN MILLER: This is not going to be, like, a rave party drug. You’re not going to be glowing or something. But instead, it’s something that potentially could be used for getting signals from mammalian cells or tissues, and being able to create reporters of particular enzymatic activity that utilize a potential endogenous luciferase activity.

IRA FLATOW: Mhm. Now Sarah, let’s get back to talking about why fireflies light up to begin with. We’ve all been told that this is a mating ritual, right?

SARAH LOWER: Yes. So each firefly species has its own flash pattern that it does, sort of like a code, a Morse code that they use to identify, locate, and choose mates. It’s also used potentially for deterring predators. All fireflies light up in the larval stage. So they’re not using light for mating at that point. They don’t have reproductive organs at that point in their lives. What we think they’re using it for then, is what we call an aposematic signal, or a warning signal. It’s like this neon sign saying, don’t eat me, I’m toxic. It’s an antipredator signal.

IRA FLATOW: Don’t eat me. I’m poisonous.

SARAH LOWER: I’m toxic. There was an estimate from Thomas Eisner, who first was looking at toxicity, and he estimated that you would have to eat about 20 fireflies to die, as the average human.

IRA FLATOW: Wow.

SARAH LOWER: I do not recommend that.

IRA FLATOW: Do not try this at home, right?

SARAH LOWER: Yeah There was a time when I accidentally got some firefly reflex bleeding on me. So this is another antipredator behavior that they do. If a predator grabs them, or if a human grabs them a little too hard, you’ll see them ooze a bit of a white, sticky substance from part of their body.

IRA FLATOW: Right.

SARAH LOWER: And that’s actually the insect equivalent of blood.

IRA FLATOW: Hmm.

SARAH LOWER: And if you get that on you, on your hands, and accidentally, say, touch your face, you might taste something really gross and your lips might go numb. So I do not recommend, based on personal experience, licking fireflies or doing any of that.

IRA FLATOW: Wow. You recently published a study about how fireflies use their sense of smell to communicate. I mean, who knows? I always assumed that they only communicate with their flashing light bulb.

SARAH LOWER: Yeah. Most people, when you think of fireflies, think of summer nights filled with flashing lights. But actually, there are many species around the world who have lost the ability to light up in the adult stage, and they come out during the day. So even if they could light up, light isn’t going to be very successful. Think about using a flashlight during the day. And so these species, we think, use smell to communicate.

They’re using a pheromone that females emit and males can follow through the air back to the female.

IRA FLATOW: How do you discover that they could smell? I mean, you can’t ask a firefly, right?

SARAH LOWER: So a lot of insects use smell for mating. A lot of the time, you can look at their behavior. So in fireflies, they’ve done experiments where you stick females out in a dish out in a field, and males will just flock to this female, even if they can’t see her, suggesting that their smell.

Or you can look at their antennae. So some fireflies have these gorgeous, what we call plumose antennae. And they’re very elaborate and flamboyant and branched. They look like antlers. And that’s a sign that maybe smell is really important, because they’re increasing the surface area of their antenna, which is the smell organ in an insect.

IRA FLATOW: Very cool. Steve, let’s go back to talking about bioluminescence and luciferin used for medical research. Can you give me a little capsule of what it’s being used for?

STEPHEN MILLER: So bioluminescence is a great way to spy on otherwise invisible processes that are occurring in live cells and animals. So it’s frequently used to monitor cell growth, such as the growth of a tumor in an animal, or the expression level of different genes, where the intensity of the bioluminescence corresponds to how highly the gene is being expressed. We’ve done things, and others– people have modified luciferins in order to make them report on different specific enzymes within cells or within animals.

They can also be used to detect, say, metals or small molecules, other things that you wouldn’t normally be able to see, but you link them to the bioluminescent light reaction. And that intensity and location tells you where and how much that enzyme, or small molecule, is being produced. Lots of things you would use for, say, drug development and testing.

IRA FLATOW: I understand that you’re working on making even better bioluminescent methods by changing the color of the light, its frequency. Tell me about that.

STEPHEN MILLER: Yeah, so the yellow-green light you see in the fireflies, it’s based on the structure of the luciferin molecule that the firefly makes. And we’ve made many synthetic analogs of luciferin, where we’ve designed it to be a substrate, but to emit light at longer wavelengths. And often, the luciferase enzyme is promiscuous enough to accept these molecules.

And so this is useful, in particular, if you’re imaging in live animal. You want to redshift the light output as much as possible because yellow-green light doesn’t penetrate very deeply through tissue. Red light penetrates more, But. The best would be in just beyond the visible wavelength region, in what’s called the near-infrared. And that’s where tissue is most transparent to light. So any bioluminescence you have in that region will penetrate better through tissue, allow you to image deeper within the organism, and be more sensitive.

IRA FLATOW: Very interesting. Sarah, as we get close to wrapping up, I want to know if you have some advice for folks who want to attract fireflies to their backyards this summer.

SARAH LOWER: If you’d like to attract fireflies to your yard this summer, the best thing to do is to turn out your lights.

IRA FLATOW: Really, they don’t like– they don’t like your light being on. Don’t compete with them.

SARAH LOWER: Light pollution is a problem for fireflies.

IRA FLATOW: Yeah.

SARAH LOWER: As you can imagine, if there’s a really big light source in the area, any females that are replying to males can’t be seen, and so mating doesn’t happen and you don’t get the next generation. In addition, larvae on the ground that are also using light as this antipredator defense, their light is not going to be seen. And so they might have some problems as well. So please, just turn off your lights during firefly time.

Other things you can do would be to create dark spaces in your yard. So maybe you can plant some tall trees or tall bushes. Maybe there’s part of your yard that you can leave with tall grass. We know that fireflies really need moisture. And so having areas of your yard that are moist, organic, rich, and dark is the way to go.

IRA FLATOW: Can our listeners be citizen scientists here and report what they see someplace?

SARAH LOWER: We would love folks to help us learn more about where and when fireflies occur. In North America, there’s a project called Firefly Atlas that’s run out of the Xerxes Society. And this is a website where you can go and you can tell us when and where you have seen fireflies. And it’s added to this growing database of sightings that then scientists like me and my collaborators, we can take that data and we can use it to model fireflies and where they occur.

IRA FLATOW: Fascinating. Fascinating. And you have still a whole lot of hot weather and summertime left to go out and catch them.

SARAH LOWER: I am hoping.

IRA FLATOW: People still catch them?

SARAH LOWER: Yeah, they are. I saw them out last night. If everything is good and it remains warm and moist, a few years ago, I saw them all the way to October, in Pennsylvania.

IRA FLATOW: You shouldn’t keep them in the jar forever, right?

SARAH LOWER: We do not advise keeping them in the jar forever. Catch and release is what we would like, if you must catch. Most firefly species that we think about only live for about two weeks as an adult in the wild.

IRA FLATOW: Wow.

SARAH LOWER: So they have 14 nights to find each other. And in those 14 nights, some species are only active for about 30 minutes. So if you keep them in a jar for one night, you are dramatically decreasing their opportunity to find a mate.

IRA FLATOW: Do not fool around with firefly romance here.

SARAH LOWER: Exactly.

IRA FLATOW: Let it happen. Thank you, Dr. Lower, for taking time to be with us today.

SARAH LOWER: You’re very welcome.

IRA FLATOW: Dr. Sarah Lower, Associate Professor of Biology at Bucknell University, based in Lewisburg, Pennsylvania. Doctor Miller, thank you also for taking time.

STEPHEN MILLER: Thanks for having me on.

IRA FLATOW: You’re welcome. Dr. Stephen Miller, Professor of Biochemistry and Molecular Biotechnology at the UMass Chan Medical School, based in Worcester, Massachusetts.

Copyright © 2025 Science Friday Initiative. All rights reserved. Science Friday transcripts are produced on a tight deadline by 3Play Media. Fidelity to the original aired/published audio or video file might vary, and text might be updated or amended in the future. For the authoritative record of Science Friday’s programming, please visit the original aired/published recording. For terms of use and more information, visit our policies pages at http://www.sciencefriday.com/about/policies/