NC scientists shed light on mysteries of fireflies

Gloria McComas catches fireflies in her yard in Woodbine, Md., in June 2011.
Gloria McComas catches fireflies in her yard in Woodbine, Md., in June 2011. MCT

When you’ve gotta glow, you’ve gotta glow – and it’s that time of year for fireflies. Each June, nature’s little sparklers, also known as lightning bugs, brighten the night.

Actually, these critters aren’t flies or bugs. They’re beetles, with more than 2,000 species. Four entomology experts from North Carolina universities shed some light on firefly mysteries.

What makes them glow – and what’s the point?

Professor Fred Nijhout at the Duke University Department of Biology said, “The light they produce is a chemical reaction that requires a few chemicals and a little bit of ATP, a molecule that supplies energy. When those chemicals are mixed – which is what happens when you squash a firefly – you get a bit of light until the energy of ATP is used up.”

Can you attract them?

Their glowing is all about courtship: Just give them a little false hope. Nijout said, “Males of the most common species in our region fly at dusk and emit light in a ‘J’ pattern, meaning that the male swoops upward while it emits light. The female of this species responds with a brief flash about three seconds after she sees this.

“If you see a male doing a ‘J’ and aim a small penlight at him, do a slow count to three and flash your penlight, you can attract the male to fly toward you. Once nearby, they figure out you are not a real female and lose interest.”

Where are they most common?

“Fireflies are most abundant and diverse in the Eastern United States,” said Clyde Sorenson, entomology professor at N.C. State. “This is because most species of these fascinating little beetles are adapted to humid-climate areas with abundant growing-season precipitation.”

Why do some of them flash simultaneously in groups?

Stan Schneider, a professor in the Department of Biological Sciences at UNC Charlotte, said this isn’t well understood. “But this synchronization happens in Asian species and has also been reported in the U.S. By all flashing at once, males may give a much stronger, more noticeable ‘collective signal’ that better attracts females. Also, by all flashing at the same time, it may make it harder for predators to find and catch any individual firefly.”

Does glowing make them an easy after-dark snack?

“Like many other insects, they produce chemicals in their body that taste bad or are poisonous,” said Matt Bertone, entomologist with the N.C. State Plant Disease and Insect Clinic. “When a predator tries to eat the firefly, it gets a dose of these chemicals and a foul taste in its mouth. These predators will then learn to avoid all insects that look like fireflies, and this is actually one of the reasons there are so many firefly lookalikes.”

Which lightning bug species draws the most scientific interest?

“Probably the most famous – or infamous – are the ‘femme fatale’ fireflies in the genus Photuris. Once they’ve mated with the males of their species, they watch for males of Photinus fireflies and mimic the return signals of Photinus females. When the Photinus males descend to mate, the female Photuris capture and eat them, collecting a chemical found in the male Photinus that the Photuris use to protect their eggs in the process.”

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