Science Friday
Hosted by Ira Flatow
Fireflies' unique body chemistry has led to advances in medical imaging. And scientists are now learning how they communicate using smell.
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Hey, it's Ira Flatow, and you're listening to Science Friday.
Today on the show, we illuminate some surprising firefly science. Like, did you know that they're toxic if you eat one?
You would have to eat about 20 fireflies to die as the average human.
One of my favorite sights 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 Lauer, 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.
Thank you so much.
Thank you.
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.
So what most people don't realize is that there are more than 2,000 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.
Right.
But there are other species that are much more rare. And those are the ones that we are particularly concerned about.
Now, what determines how good a quote unquote crop of fireflies we have in any one year? Are there environmental issues?
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.
What if it's really rainy out? Does that affect, you know, the population?
Some of the reports that we've been hearing this year from people, especially in like 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.
Yeah, yeah. Well, what about fireflies in urban areas? Do they live a different life, have a different population dynamic?
So I just got done with the International Firefly Symposium in Tlaxcala, Mexico.
There is such a thing.
There is, and anyone who is a firefly enthusiast, scientist, educator, storyteller, artist is welcome to come and contribute. One of the things that 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.
Wow, that is very interesting. Okay, 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?
Yeah, so fireflies are beetles that they chemically emit light when an enzyme they produce, firefly luciferase, acts upon a small molecule they make called deluciferin 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.
So we know why fireflies glow up, but but do other insects or animals have this ability also, Steve?
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, we're studying fruit flies. And we asked, you know, 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, you know, mercifully, fruit flies do not glow in the dark. 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, just give it a new substrate and we see light emission.
That must have been spooky.
It was spooky, but it was cooled 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.
I'm just letting that sink in for a second. Would you use it internally as a diagnostic or how would you use it?
This is not going to be like a rave party drug. You're not going to be glowing or something. But instead, you know, 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.
Now, Sarah, let's get back to talking about why fireflies light up to begin with. We've all been told that this is sort of a mating ritual, right?
Yes, so each firefly species has its own flash pattern that it does. It's 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 eposematic signal, or a warning signal. It's like this neon sign saying, "Don't eat me, I'm toxic." It's an anti-predator signal.
"Don't eat me, I'm poisonous."
"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.
Wow.
I do not recommend it.
Do not try this at home, right?
Yeah. There was a time when I accidentally got some firefly reflex bleeding on me, so this is another anti-predator 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. And that's actually the insect equivalent of blood. And if you get that on you, and on your hands, and accidentally you 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.
Well, 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.
Yeah, most people, when you think of fireflies, you 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.
How do you discover that they could smell? I mean, you can't ask a firefly, right?
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 they're smell. Or you can look at their antennae. So some fireflies have these gorgeous, what we call plumes, 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.
After the break, how the firefly's glowing lantern is used in medical research.
Bioluminescence is a great way to spy on otherwise invisible processes.
Stay with us.
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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?
So I mean, 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, like, say, drug development and testing.
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.
Yeah, so the yellow-green light you see the fireflies, it's based on the structure of the luciferin molecule that the firefly makes. And we've made many synthetic analogues of luciferin, where we've designed it to be a substrate but to emit light at longer wavelengths. And often, the luciferous enzyme is promiscuous enough to accept these molecules. And so this is useful, in particular, if you're imaging a live animal, you want to red-shift 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.
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?
If you'd like to attract fireflies to your yard this summer, the best thing to do is to turn out your lights.
Really? They don't like, they don't like your light being on. Don't, don't compete with them.
Light pollution is a, is a problem for fireflies. 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 anti-predator 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. Although the 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.
Can, can our listeners be citizen scientists here and report what they see someplace?
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. It's run out of the Xerces 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.
Fascinating, fascinating. And you have still a whole lot of hot weather and summertime left to go out and. Catch them.
I am hoping.
People still catching them?
Yeah, they are. I saw them out last night. If everything is good and it remains warm and moist, um, a few years ago, I saw them all the way to October in Pennsylvania.
You shouldn't keep them in the jar forever, right?
We do not advise keeping them in the jar forever. Catch and release is what we would like if you must catch. Um, most firefly species that we think about only live for about two weeks as an adult in the wild. 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.
Do not, do not fool around with firefly romance here.
Exactly.
Let it happen. Thank you, Dr. Lauer, for taking time to be with us today.
You're very welcome.
Dr. Sarah Lauer, Associate Professor of Biology at Bucknell University, based in Lewisburg, Pennsylvania. Dr. Miller, thank you also for taking time to be with us today. Thanks for having me on. You're welcome. Dr. Stephen Miller, Professor of Biochemistry and Molecular Biotechnology at the UMass Chan Medical School, based in Worcester, Massachusetts.
Hey, thanks for listening. This episode was produced by Soshana Buxbaum. See you next time. I'm Ira Flatow.
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