Fireflies light up the summer sky

July 7, 2010 under CANR News

Fireflies may not light up the sky as bright as Fourth of July displays but this season they’re putting on quite a show.

“This is a fantastic year for fireflies, probably because we got so much rain last summer,” says Doug Tallamy, chairperson of the Department of Entomology and Wildlife Ecology at the University of Delaware. “As larvae, fireflies like moist leaf litter and things stayed moist last year.”

“Nature’s fireworks” continue long after July 4th — fireflies are at their peak now and stick around Delaware until the end of July.

Although most of us call them fireflies or lightning bugs, these luminescent creatures are more properly known as Lampyridae, which in Latin means “shining fire.” And they are actually beetles, not flies, says Brian Kunkel, an entomologist with UD Cooperative Extension.

Summer out West certainly has its pleasures, such as less humidity in most places than here in the Mid-Atlantic. But one thing you can’t enjoy in Beverly Hills or Boise is fireflies.

“Fireflies aren’t found west of the Rockies,” says Kunkel.

There are several species of fireflies native to Delaware. The beach region of Sussex County is home to the coastal firefly, which prefers sandy, even salty, soil and generally stays close to the ground. Inland Sussex and Kent counties are home to yet another species. But the greatest diversity in firefly species is found north of the Chesapeake and Delaware Canal, says Kunkel.

“Fireflies are especially abundant in the piedmont region, in the northernmost part of Delaware,” he says. “Most firefly species favor ‘old field habitat.’ In New Castle County, that type of habitat is most commonly found around the White Clay and Red Clay creeks and along the Brandywine River.”

At first glance, one species of firefly may not look much different from another. But pay close attention to fireflies as they begin to light up. “If you look closely, you’ll start to notice some distinct variations,” says Kunkel.

There are three characteristics that differentiate firefly species:

  • Where the fireflies are located. Some species like to be very close to the ground; others prefer shrubs and low trees.
  • The flight track, or style of flying, varies from species to species. Some fly in a “J” pattern then swoop down low, others take looping flights.
  • The pattern of the bug’s flashing. Think of the flashes like Morse Code — do they resemble a dash-dash-dash pattern or dash-dot-dash?

As for why fireflies light up, it’s for the same reason that tight clothing and flashy jewelry are a staple at nightclubs — to attract the opposite sex. Adult fireflies, both male and female, flash coded messages to attract prospective mates. Males fly about while they flash, females usually flash while hanging out in bushes. It’s all about “speed dating” not lengthy courtships — there’s no time to waste since adulthood lasts just two weeks.

There’s also another reason why fireflies light up, at least in the case of juvenile larvae. Almost a decade ago, UD scientists led by Tallamy discovered that baby fireflies light up to keep predators at bay.

Previous studies had shown that mice and other would-be predators shun adult fireflies because of a compound in fireflies’ body that produced a bitter taste. The UD study demonstrated that baby fireflies flash to advertise that they also exhibit this bitter taste.

“A flashing neon sign may lure hungry humans to an all-night diner but the bioluminescence of firefly larvae sends a very different message to would-be predators,” says Tallamy.

If your kids like to catch fireflies and put them in a jar, go for it, says Kunkel, as long as you punch some holes in the lid and release the fireflies after a few hours. Fireflies are beneficial insects because they may feed on insect pests in the garden so it’s important not to harm them.

Article by Margo McDonough

You can also see this article and accompanying photo on UDaily by clicking here.

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