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Curious City

Why Chicago Lightning Bugs Light Up One Neighborhood But Not the Next

Erin Pavlich grew up in suburban Western Springs and has fond memories of running around her neighborhood in the summer, catching fireflies. (Or lightning bugs — she, like many of us, uses the names interchangeably.)

“I had a little screen bughouse that I would catch them in, and usually they would die by the next day if I kept them in the bughouse. But it was something I really liked doing,” she says.

These days — some twenty-odd years later — she lives in Glen Ellyn and she can’t net so many fireflies.

“Now that I have kids of my own, it’s something I’d like them to enjoy doing,” she says. “But it just doesn’t seem like they’re as copious as they used to be.”

So Erin wants to know: What happened to all the lightning bugs? And, will this new generation of Chicago kids be able to have the same bug-jar-in-the-front-yard experiences she did?

For answers, we rounded up two experts who know a thing or two about bugs, in Illinois and beyond: Doug Taron, chief curator of the Chicago Academy of Sciences at the Peggy Notebaert Nature Museum; and May Berenbaum, professor and head of entomology at University of Illinois Urbana-Champaign.

Let’s start with why our questioner, Erin, and everyone else notices lightning bugs in the first place: Why do they light up?

Taron: It’s how they mate! The males are generally the ones that are flying, and they do the vast majority of the flashing. The females are usually perched on vegetation.

Each species of male has its own flash pattern and the male will fly around, periodically signaling with its flash pattern. It's sort of like, “Hey baby, hey baby, hey baby.” If there is a receptive female of the correct species, she will wait a precise time interval ... and give just a single flash burst. Then he’ll fly down, they’ll mate, and then she will go off and lay eggs.

What affects lightning bug populations in general?

Berenbaum: There’s suggested evidence that changing nighttime illumination patterns might have an impact on, for lack of a better word, their sex life. Just recently, a study was published in a small journal that suggests that nighttime illumination actually does have an adverse effect on males.

The ability of males to find females seems to be affected by artificial lighting. So if you’re anxious about fireflies, turn off your lights.

Plus, the chemical industry for years has been using firefly chemicals to detect the presence of ATP, which is the presence of living cells. For years, there was a chemical company paying people a penny a firefly to collect them! That seemed to be having an impact. An estimated 3 million fireflies a year were caught for biochemical assays.

Taron: One thing that's pretty clear about firefly populations is, as is typical with many insects, the population seems to vary a lot from year to year. Rainfall probably has a lot to do with it, because that influences the food supply — not so much for the adult fireflies, but for the larval forms. The larval forms don't fly; they’re really bizarre-looking creatures. They look sort of armor-plated, and they eat things like tiny snails, slugs, [and] roly polies. These are things that live in moist soil, so their food supply tends to go up in years with good rainfall and therefore you get a lot better firefly survival through the larval stages.

Now, the heart of Erin’s question: Have lightning bug populations in Illinois changed over the last few decades?

Berenbaum: It’s hard to say what the long-term, baseline trends are because we don’t have that information. It’s difficult to figure out what’s going on with fireflies because for far too long, people haven’t been paying attention to them.

Taron: We don’t really have a good answer to that yet. A lot of the focus of research on them has been about their luminescence instead of their numbers.

I’m glad to know there’s no lightning bug crisis.

Berenbaum: I don’t know that we can say there’s no crisis, because we don’t have the numbers. But we do know that for years they were unsustainably harvested, and at the same time a lot of their habitat was being destroyed. So I think people should be mindful.

Taron: Recently, with citizen science becoming a big thing, there are some programs — in particular The Firefly Watch out of the Museum of Science in Boston — that are seeking to crowdsource population studies. People are reporting firefly observations, so with some persistence, in a few years we'll start to get better information about long-term trends of firefly populations.

One thing I learned was that the lightning bug population is indeed very local. During my reporting, I introduced Erin to a spot that’s actually pretty close to her home: Bluff Spring Fen, a wet, prairie-like spot near Elgin. It has lightning bugs out the wazoo. The fact that Erin’s home has very few, and the fen has many, shows that lightning bug populations are “local.” How local are we talking about?

Berenbaum: Definitely not a yard, but they do tend to be fairly localized. Maybe across your neighborhood.

Questioner Erin Pavlich and Doug Taron, chief curator of the Chicago Academy of Sciences at the Peggy Notebaert Nature Museum, visit Bluff Spring Fen near Elgin to look for the lightning bug density Erin remembers as a kid. (WBEZ/Sean Kennedy)
Other than local rainfall, what might affect a particular local population of lightning bugs?

Berenbaum: A big redevelopment in your neighborhood could cause a change. If you’re paving over soil, then that’s going to have an impact on everything that otherwise depends on that soil.

Taron: Fireflies don’t seem to do well is some of the really modern housing developments, where they take away all of the topsoil and put back a thin layer of topsoil. Most of the critters that fireflies need kind of go away and don’t really come back while under those conditions.

Fireflies like low, leafy vegetation. There's much more of a push today for much more chemically intensive lawn management, where you don't have things like clover and other things growing among the grass, and you get that by using a lot of pesticides on your lawn. It’s possible for that to have an effect on something like firefly populations. But has it had an effect? We don't know that at this point.

How’s the 2016 season been for lightning bugs?

Berenbaum: Down here in central Illinois, it’s a boom year for fireflies. They’re quite abundant and conspicuous, and actually fairly early [first showing up in early June]. They usually last through the end of July.

Taron: This year appears to be a good year! We're just getting started here, so it'll be interesting to see how it goes. Chicago is usually a little bit behind downstate.

What’s the best way to get in a good light show?

Taron: A lot of people are going to be able to do firefly spotting in their yards, which is great. If you want some place easy to get to, you can go to an older residential neighborhood and just stroll around on the sidewalks. The best time seems to be right around dusk; they really seem to quiet down an hour or two hours after sunset, so it's not a really late-night thing. The bigger light shows that I've seen, you want to go to a wetland. They like humid places with a lot of vegetation.

A composite image that only hints at the many lightning bugs we saw when we took our questioner out to Bluff Spring Fen, near Elgin. (WBEZ/Sean Kennedy)
About our experts

May Berenbaum is a professor and head of entomology at University of Illinois Urbana-Champaign. She focuses on herbivorous insects and pollinators.

Doug Taron is chief curator of the Chicago Academy of Sciences at the Peggy Notebaert Nature Museum in Lincoln Park. He’s also a steward of Bluff Spring Fen in Elgin.

More about our questioner

Erin Pavlich is a compliance officer at a financial services firm. She grew up catching fireflies in suburban Western Springs, but doesn’t seem to be netting as many in her new home in Glen Ellyn. Her two kids aren’t quite to lightning-bug-catching age yet (they’re ages 1 and 3) but she wants to make sure they can have as many long nights with a mason jar full of lightning bugs as she did.

“I think I might take a look at my landscaping to see if there’s some areas we can encourage some more natural environments,” she says. “Maybe we can incorporate something that’s more conducive to lightning bugs.”

Sean Kennedy is a reporter in Chicago. Follow him @stkennedy.

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