Catching Fire

The Science of Lightning Bugs

Catching Fire
Biology major Sarah Sander ’06 is part of a team that plans to decipher the firefly genome.

The flat light of dusk settles over a small meadow in western New York. Trills of tree frogs mingle with the songs of nearby catbirds and the occasional whine of a mosquito. The grass is tall on this warm July evening, in some spots rising over the head of Sarah Sander ’06. She’s in her full field regalia: headlamp, stopwatch, tall rubber boots and, most important, a collapsible white net with a 6-foot aluminum handle. Just before 9 p.m., she spots the first dim flickers of yellow light amongst low tree branches: fireflies.

These bioluminescent bugs are quintessential visuals of summer evenings, at least in the eastern United States, where they use light signals to attract mates. (There are many species of fireflies out west, too, but they tend to use pheromones for this purpose.) While many of us are content to simply watch and marvel at the blinking light patterns, Sander, a postdoctoral associate at Cornell, is part of a team hoping to unravel the very nature of these beetles. Their goal is ambitious: to decipher the full genome of a firefly for the first time. To pay for their research, they’ve turned to an unconventional source: the eight researchers have brought in $10,000 via an online crowdfunding campaign.

Catching Fire
Although it's difficult to imagine when surrounded by hundreds of blinking lights, there is some evidence that firefly populations may be in trouble.

With a decoded genome in hand, researchers will have a better handle on how, exactly, fireflies produce light. “We know the basic players, but we don’t really know how they’re made or regenerated,” says Sander. Two of the fundamental components involved in the light-making—an enzyme called luciferase and a substrate called luciferin—have extensive biomedical applications. They are used to monitor tumor growth in cancer research, for instance, and to determine what genes are being expressed in a particular organism. But scientists don’t know how fireflies make luciferin. “There’s no other natural product like it,” says another member of the firefly genome team, Tim Fallon, a Ph.D. student at MIT. 

Besides their glowing rear ends, fireflies (or lightning bugs, depending on where you’re from) have other unusual characteristics. Many of the 150 or so species found in the United States are toxic, Sander says, and some will actually start bleeding as a defense mechanism, extruding their toxin-filled blood when threatened, as a way to make themselves unpalatable to potential predators. 

Catching Fire
As the sky darkens, Sander checks the flash-pattern timing of a firefly she's just caught. With a decoded genome in hand, Sander and other researchers will have a better handle on how, exactly, fireflies produce light.

Others, like species in the genus Photuris, have lost the ability to make these defensive toxins; females in this genus use their flashes to lure males of a different, toxin-producing species, pretending to be females of the toxic species ready to mate. When the males approach, the larger Photuris devour them, ingesting the toxins for their own use. (Talk about a femme fatale.)

As the sky continues to darken, and the birdsongs fade, more and more fireflies blink on in the meadow. Soon, greenish-yellow flashes consume the grass, trees and air. From a distance, patterns emerge and disappear as the bugs flash in unison, only to lose the synchrony moments later, like some sort of alien Morse code. Sander is in her element. Spying a firefly, she sweeps her net back and forth in a rapid, narrow figure-8 motion, with the grace and efficiency of a well-trained martial artist. It’s a Photuris male, flashing angrily as she gently but firmly plucks it from the net and puts it in a plastic tube, where it scurries along the sides. 

Although it’s difficult to imagine when surrounded by hundreds of blinking lights, there is some evidence that firefly populations may be in trouble. In the United States and globally, says Lynn Faust, an independent firefly researcher who has worked with Sander in the past, reports of shrinking or disappearing populations abound. “Everyone agrees they remember more as children.... I have watched, personally, population after population disappear,” Faust says, citing habitat destruction, pesticide use and light pollution as likely causes. 

But what’s important to people like Faust and Sander is scientific proof. Are these apparent trends merely anecdotes, or are they true causes for concern? While the genome work won’t directly answer that question, Sander says, it can play an important role in firefly conservation, by identifying which populations have the most genetic diversity and are therefore most important to conserve. 

Catching Fire
In the lab, scientists use two of the light-making components found in fireflies to monitor tumor growth in cancer research. Sander's job will be to make sense of the genome, figuring out where each gene is and what it does.

Adult fireflies live for only about two weeks, an urgent frenzy of flashing in a desperate effort to find a mate. The eggs that females lay hatch later in the summer; the larvae overwinter and then usually pupate the next summer. The larvae also glow, although more dimly and without the rhythmic flashes, possibly as a warning to predators that they’re toxic. Scientists have removed the light-emitting organs from the larvae, only to find that when those larvae become adults, they can still light up just fine. That means, says Sander, that they create a brand new light-emitting structure between their larval and adult stages. 

Sander has collected seven fireflies tonight. She will pair up some of them up to see if they’ll produce larvae to raise in captivity. “I’ll put the female in with this male and see if we get babies,” she says. “Or, if she eats him. Sometimes we get both.” These fireflies are of a different species than those in the genome project, but Sander and a collaborator hope to use the new larvae she produces this summer to study other aspects of firefly genetics.

At Amherst, Sander also studied flying, flashy creatures: not fireflies, but hummingbirds. “I’m a sucker for charismatic organisms,” she says. Assembling the full firefly genome will make use of her Ph.D. work, which involved looking at shorter segments of the firefly genome. She’ll also be in charge of making sense of the genome, by taking the long strings of letters that represent nucleic acid and figuring out where each gene is and what it does. 

Grants for this kind of research are hard to come by, which is one reason Sander and her team chose to pursue crowdfunding. But there’s a second reason, she says: “We thought it was a great way to reach out to the wider community, scientists and nonscientists, and involve them and show them what we can do with their support.” Many of their backers sent detailed messages about how much they have loved fireflies since childhood.

By now, the light has completely faded from the moonless sky. Apart from Sander’s headlamp, the blinking bugs are the only source of light. On a warm night such as this, they might keep flashing past midnight. At the parking area we stop to admire the lights. The trees look like a Christmas display. “People don’t go outside in the dark,” Sander tells me. They perceive the darkness as full of threats and unpleasant bugs. That may be true, but it’s also full of strange and mysterious beauty—beauty that Sander’s research is helping to make a little less mysterious. 

 

Want More Fireflies in Your Yard? 

IF YOU WANT more fireflies in your own yard—and who wouldn’t? —try turning off outdoor lights at night, reducing the amount of pesticides you spray on your lawn and letting your grass grow a little longer in the summer. Or, better yet, leave parts of the lawn totally unmowed. But no need to overthink it. “Best practice is just: turn out all your lights, go out on your porch and watch,” says Sander. In the words of a fellow firefly researcher, Lynn Faust: “They are one of the few insects we are not trying to kill,” thanks to the “beauty and mystery and awe” that they offer the world.