ANNIE MINOFF: One of the trademark signs of summer is the flickering dance of fireflies in the evening, and a comment you hear a lot when you’re talking about fireflies is, you know, I don’t see as many as I used to. But is that actually true? And if so, is there anything that people can do to help improve firefly numbers?

Joining me to talk about that is Dr. Sarah Lower, Assistant Professor of Biology at Bucknell University, and she’s one of the coauthors of a recent paper looking at firefly numbers published in the journal Science of the total environment. Dr. Lower, welcome to Science Friday.

SARAH LOWER: Thank you so much.

ANNIE MINOFF: So is that something that you hear a lot from people as a firefly researcher? Do they say, where did all the fireflies go?

SARAH LOWER: I have heard, Where do all the fireflies go? or Where have all the fireflies gone? since I started firefly research about 13 years ago. That is one of the most frequent questions.

ANNIE MINOFF: And what do you tell people?

SARAH LOWER: Well, it used to be that I would say, you know, I hear that a lot, but we don’t have a lot of data backing that up. More recently, we’ve been getting more data from around the world, different parts of the world, to actually document these declines. And it doesn’t seem to be for every species, but for some of these species, that seems to be the case.

ANNIE MINOFF: And this study, as I understand it, looked at a ton of citizen-science observations. So tell me about that. What were people looking for?

SARAH LOWER: So this work was done in collaboration with Darin McNeil from the University of Kentucky and researchers at Penn State, including Christina Grotzinger, Sarah Goslee, Melanie Kammerer, and John Tooker, as well as collaborations with the USDA. And it’s based on data gathered from a citizen-science project. So this is when we get people who are interested in helping us figure out where fireflies occur. They go out in their backyard or if they’re out camping or hiking, wherever they are. They actually log their firefly sighting into this database. It’s online.

And so over time, this collected over 20,000, I think, observations, and we can use all of those data points to then do some modeling about, What are potential threats to fireflies? and what are potential places where we expect fireflies to occur? What’s a good firefly habitat look like?

ANNIE MINOFF: Well, let’s follow up on that. What is a good firefly habitat? If I’m a firefly, kind of what do I need to thrive?

SARAH LOWER: So for the sightings that we looked for in this study, which were most dominated by firefly species that are really common and abundant and active around sunset when most people are out grilling or whatever you– catching fireflies with your kids, that sort of thing. With this data set that was probably dominated by those species, firefly habitats are dark– so they don’t include a lot of artificial light– moist– so they have a lot of organic matter in the soil that helps retain moisture and, if a drought happens in the summer, sort of buffered against that really intense heat and lack of moisture.

It also is fairly clear of impervious surfaces, so not a lot of concrete or asphalt. There are ways for fireflies to get to the soil, to lay their eggs, and to be larvae. So they spend one to two years as a larva.

ANNIE MINOFF: Wow.

SARAH LOWER: Yes.

ANNIE MINOFF: That’s a long childhood.

SARAH LOWER: If you think about it, the fireflies that you see this year are actually the parents of the ones that you’ll see two years from now, potentially, and they actually may be the offspring of the ones you saw two years ago.

They are predators. They eat soft-bodied invertebrates like slugs and snails and worms. And so you need these moist areas with access to the soil to be able to have a good larval environment.

ANNIE MINOFF: So you know what fireflies need. You have all of this citizen-science data. What does it take to actually say whether there are, in fact, fewer fireflies overall?

SARAH LOWER: So for that, we are going to need way more data, and this is when this opportunity to speak with you offers me a great platform to encourage your listeners.

ANNIE MINOFF: Are we recruiting right now?

SARAH LOWER: We are recruiting. We would love to get more people involved with helping us find out when and where fireflies are occurring so we can actually figure out, are declines happening? Where are they happening? What species are they happening to? And all of this can be done in concert with the Firefly Atlas project. So this is run through the Xerces Society. There are training documents online on how to fill out the observation forms, and it will all be curated and added to this growing database of firefly sightings that we can use in the future.

ANNIE MINOFF: So like with monarch butterflies, for example, people talk about planting the right kind of milkweed to help that species out. Is there anything equivalent that I could do to help fireflies in my area?

SARAH LOWER: With fireflies, they are not pollinators that we know of. They do not have a host plant that we know of. But what you can do on your own in your own backyard or your own business is to practice firefly-friendly land management. So, for example, you could, if you have bright lights around you, plant trees that will grow up and provide dark environments in part of your yard. You could turn off your lights or set them on some sort of timer so that they turn off after a certain period and will have less impact on the fireflies. You can leave part of your grass long.

ANNIE MINOFF: Another excuse not to mow the lawn.

SARAH LOWER: Yes, no mow May–

ANNIE MINOFF: It’s good for fireflies.

SARAH LOWER: No mow May can extend the entire summer. We have an initiative called Lights Out for Lightning Bugs, which is for a period of time in the summer, you actually turn off your lights during firefly mating period, and we actually encourage folks to go out and just sit out and enjoy the light show.

ANNIE MINOFF: OK, so what I’m hearing is that you shouldn’t mow the lawn. Trees are great. Darkness is great. What about stuff like pesticides, if I use pesticides on my lawn?

SARAH LOWER: We are recommending trying to use very specific chemicals, so not broad-spectrum insecticides. And, in fact, if you cannot spray at all, that would be the best practice. However, if you’re thinking of using some organic methods, things like using BT, Bacillus thuringiensis, which is a bacterial insecticide that can be very specific to a particular insect that you’re targeting, that might be the safest way to go.

ANNIE MINOFF: So you’ve been talking about firefly species, and I think I always assumed it was just one animal. So tell me about some of these different species. Do you have a favorite firefly?

SARAH LOWER: There are over 2,400 described species of firefly around the world.

ANNIE MINOFF: Wow.

SARAH LOWER: And in North America alone, there’s probably over 180 now. Just last month, a description of three new species on the East Coast just showed up. So we are still discovering new species.

My favorite species is the blue ghost firefly. So this is a firefly that you can find in the Smoky Mountains. I recently heard of populations starting to appear up the Appalachian range, and this is a species that glows. So it doesn’t flash. It actually sustains its glow, and it sort of floats around in the forest. It looks like fairy lights.

ANNIE MINOFF: Is it possible for a normal person, me, to tell fireflies apart by eye? Is that something I could learn how to do?

SARAH LOWER: You could totally learn how to do that. Part of the training for Firefly Atlas includes some informational videos on how to identify different species. You can look at their flash patterns. So each species emits its own pattern of flashes, and so you can tell species in that way. Different species can be different colors. They signal in different habitats at different times of night. And so some of the trainings for that include documenting that information so that even if you don’t know what the species is, we can go back in later and say, this is likely this particular species given this data.

ANNIE MINOFF: So maybe if you’re a birder and that’s gotten a little old, you’re looking for something new, maybe firefly-species identifier is your next hobby. I don’t know.

I understand that this is fieldwork season for you, so what does that look like as a firefly scientist?

SARAH LOWER: Fieldwork for a firefly scientist is like the best day ever. It’s also one of the longest days ever. So you are going out in the field. You take your net. You take your hat to prevent getting spiderwebs in the face. You take your headlamp. You have your stopwatch to time flashes. You have lots and lots of things to keep fireflies in. So instead of big, heavy mason jars, we actually have little plastic tubes that we’re using to catch them and look at them closely.

And you go out about 30 minutes before sunset to explore your site. And once it starts getting dark, frogs start coming out. Crickets start coming out and then the fireflies. And it’s just– kid in a candy store is not quite the right analogy, but it is amazing.

Most people think of fireflies coming out at night or at sunset with those beautiful bioluminescent flashes, but, actually, many species have lost the ability to light up as adults, and instead they come out during the day. They do not emit light, and we think that they might be using pheromones to communicate. And so my fieldwork also involves going out in the daytime and collecting fireflies. So we are on at 8:00 AM, 9:00 AM, and we go all the way up to 10:00, 11:00 at night.

ANNIE MINOFF: Wow. That’s a long day. I understand that you frequent firefly festivals. I don’t think I’ve ever heard of a firefly festival.

SARAH LOWER: There are firefly festivals around the world. There is one near us near Bucknell University in Pennsylvania, the Pennsylvania Firefly Festival. It is every June towards the end of June, and it coincides with the emergence of the synchronizing firefly Photinus carolinus. So this is a firefly that emerges and will actually sync up its flashes so that you have the whole section of forest pulsing together.

It’s most well known from the Smoky Mountains, so there is a lottery system now to get tickets to go and see the annual emergence of Photinus carolinus down there. It is absolutely phenomenal. If you get a chance, definitely do it.

But we also have them. They go up the mountain range, and we also have them in Pennsylvania in Allegheny National Forest.

ANNIE MINOFF: That sounds like quite a show. Dr. Sarah Lower, assistant professor of biology at Bucknell University, thanks for taking time to talk with me today.

SARAH LOWER: Thank you so much for having me.

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