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Summer's Silent Spectacle

Summer's Silent SpectacleTufts professor Sara Lewis, who has researched fireflies extensively, explains the purposes behind their dazzling light shows.

Medford/Somerville, Mass. [07.23.07] After Red Sox games and barbeques, nothing signals the arrival of summer in New England like the flashing of green lights in the night. While the bombastic Fourth of July fireworks show in Boston may be flashier, a subtler presentation can be seen just about every summer night: the complex display of the firefly.

"Fireflies are arguably the most charismatic of all insects," Tufts biology professor and firefly research Sara Lewis told the National Geographic Channel. "Every kid knows that fireflies are magical sparks in the night."

Lewis has been studying fireflies and other beetles (fireflies are actually a type of beetle) for much of her career. In a recent column for the Lincoln (Mass.) Journal, she explained "just how much drama and intrigue lurks behind the spectacular summer lightshows put on by fireflies."

Far from being simply a "charismatic" habit, the flashing of fireflies is essential to their survival, and is used in multiple ways by different species. There are approximately 130 species of fireflies in the United States that fall into three different groups: Photinus, Pyractomena and Photuris. In New England alone, there are 30 species of fireflies.

"In Photinus and Pyractomena," Lewis wrote in the Journal, "their silent fireworks are all about mating." These fireflies spend most of their short lifespan attracting a female by communicating with their flashes. The flashing may appear random, but fireflies are really "broadcasting a courtship signal that is characteristic for each species." While the males circle above, females prefer to stick to blades of grass, admiring the spirited display over their heads.

"When a female is interested she will respond with her own flash signal," Lewis wrote, "which she delivers after a short delay." Seeing the corresponding signal, the lucky male will land nearby and flash his response. "Then a periodic back-and-forth dialogue ensues as the male scrambles excitedly up and down grass blades, searching for the stationary female." However even after eliciting a response, a male must contend with other males "attracted to the ongoing dialogues." According to Lewis, the ensuing competition can last up to an hour, but one male eventually wins.

While mating, the males give the females a "nuptial gift" of sperm and nutritious material that the female will use to help nourish her eggs. Lewis says some species of females prefer a longer flash, as that indicates a better nuptial gift.

"It's a little bit like firefly child support," she told the National Geographic Channel.

Photuris fireflies, however, use their flashing to hunt. These fireflies are larger, quicker and more active;they "are specialized predators who eavesdrop on other fireflies' highly visible courtship signals to locate their next meal." This tricky genus can simulate "the flash responses normally given by females of various Photinus species, using these false signals to lure and capture unsuspecting male prey," according to Lewis.

Lewis warns that light pollution from streetlights and outdoor house lights can interfere with the fireflies' breeding habits and disrupt their captivating display of flashing. With the right setting and mood, however, you could watch these glowing insects light up your backyard all summer long.

"Even as scientists studying fireflies for year after year after year, we still go out into the field in the summertime and are completely blown away," Lewis told the National Geographic Channel.

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