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Decoding the Flash of Fireflies

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Decoding the Flash of Fireflies

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Decoding the Flash of Fireflies

Decoding the Flash of Fireflies

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In many parts of the country, twinkling of fireflies is a sure sign of summer. It turns out that this familiar summertime phenomenon is actually a dance of courtship, seduction and sometimes murderous death — as biologists in Boston are discovering.


When you're outside in many parts of the country this time of year, the stars aren't the only things twinkling. Fireflies are a sure sign it's summer. It turns out what you're seeing is actually a dance of courtship, seduction and sometimes murderous death, as NPR's Anthony Brooks learned just outside Boston.

Unidentified Woman #1: Would you like a penlight?

Unidentified Woman #2: Thank you.


On a warm, humid midsummer night, Sarah Lewis has wrapped herself in yellow rain gear and a tight-fitting hood to protect herself from mosquitoes in a quiet field west of Boston.

Professor SARAH LEWIS (Tufts University): You ready to roll?

Unidentified Woman #3: They should start flying in, like, five minutes.

Prof. LEWIS: Five minutes, OK.

BROOKS: Lewis is a biology professor at Tufts University and passionate about fireflies. As the evening light fades and long, dark shadows stretch out beneath the maple trees, a constellation of tiny greenish lights begin to flicker and dance. Lewis says when fireflies light up like this, they're talking.

Prof. LEWIS: They are talking a lot, and they're talking about two things, primarily. They are talking about sex. The males are signaling their availability; females are responding with a flash signal to those males that look particularly good for whatever reasons. The other thing they are talking about is death.

BROOKS: So it's sort of a whole sweep of life out here.

Prof. LEWIS: Yeah. It's really cool. It's very cool. That's a firefly.

BROOKS: Males flash twice to announce their presence and desire to mate. If the female approves, she flashes once, which is an invitation to consummate the romance. Lewis says fireflies spend their entire adult lives, about two weeks, doing this--no food, no sleep, just a fiery dance of courtship and sex.

Prof. LEWIS: Becca(ph), any females?

BECCA: Just males over here, no females yet.

Prof. LEWIS: OK.

BROOKS: Lewis and her small team of assistants are studying the species Photinus greeni. They carry tiny lights that mimic the male's flash, so they can find females and study their responses. Firefly populations typically have many more males than females, so there's intense competition among males to attract a mate, which Lewis says poses an intriguing question.

Prof. LEWIS: So one of the things we've been interested in looking at is what makes males winners of mate competitions.

BROOKS: Lewis says a male's success appears to be related to the quality of its light flash.

Prof. LEWIS: In some species--for example, these guys--flashes that have shorter intervals between the two pulses are more attractive to the females. In other species of fireflies, faster pulse rates are more attractive to females.

BROOKS: Which leads to another question: Do fireflies that exhibit faster or slower pulses of light make better mates?

Prof. LEWIS: That's actually something we're really, really interested in knowing more about. In one species of firefly, Photinus ignitus, we have discovered that males that produce longer-duration flashes also deliver a more nutritious nuptial gift to females.

BROOKS: And we're not talking about carrot cake here.

Prof. LEWIS: No. During mating the males are busy transferring not just sperm to the females, but a very elegant coiled package called a spermatophore. And it turns out the spermatophores have a lot of protein in them, and the males that have slightly longer duration flashes are males that also have larger nuptial gifts to give the females.

I'm sorry, I think I see a female over here. I just wanted to...

BROOKS: Lewis runs off to collect the female in a plastic cup.

I'm amazed that you can pick out a female from 50, hundred feet away.

Prof. LEWIS: Well, you know, one of the cool things about fireflies is that you can really eavesdrop on their conversations. So you can see that here are males that are out advertising, `I'm a male, Photinus greeni. I'm a male, Photinus greeni.' Just with a penlight, you can actually imitate the flash signals of males, and you can get females to respond to you. So it's a great activity for kids 'cause you can talk to fireflies.

BROOKS: But, as Lewis said, some of the fireflies out here are also talking about death. Lewis says the species Photuris, common in many Northern states, is a femme fatale, a voracious predator that uses her flash to lure the much smaller Photinus, who thinks he's found a mate but instead meets a ghastly end.

Prof. LEWIS: Once they lure in a male, they suck the blood out of the male, and then they pretty much just chew up the rest of the body. They'll often leave the eyes and spit out the hard bits.

BROOKS: Goodness.

(Soundbite of laughter)

BROOKS: Sarah Lewis of Tufts says if Photuris fireflies were the size of house cats, people would be afraid to go out at night, and the soft, gentle glow of their nighttime presence would be anything but soft and gentle. Anthony Brooks, NPR News.

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