Annelid worms do it. Certain species of centipedes and millipedes do it. Even a tropical land snail can do it.
But here in Delaware, fireflies and glow worms are the only terrestrial creatures that light up the night with their own built-in flashlights.
Bioluminescence results from a chemical reaction in which chemical energy is converted to light energy, according to Doug Tallamy, chair of the University of Delaware’s Department of Entomology and Wildlife Ecology in the College of Agriculture and Natural Resources.
Fireflies (Lampyridae) aren’t actually flies and glow worms (Phengodidae) aren’t really worms. Both are considered to be beetles and are closely related species.
The fireflies’ glow adds beauty to a summer night but there are several pragmatic reasons for bioluminescence, too. Fireflies and glow worms light up 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 only lasts for about two weeks.
There’s 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.
This summer is shaping up to be a good but not spectacular season for fireflies.
“Lightning bug populations at my house have been strong but not record-breaking,” says Tallamy. “In general, populations fluctuate from habitat availability more than from weather. However, if we get a bad drought during the summer and fall that does impact the population of lightening bugs the following summer.”
Fresh strawberries for a few short weeks around Memorial Day. Carnival rides at the State Fair for 10 days in July. Like other summertime pleasures, firefly season is short-lived. “Nature’s fireworks” begin a few weeks before July 4th and are at their peak now. By the end of July they’re gone, save for a few stragglers.
Where to find different species
Several species of fireflies can call themselves native Delawareans. The beach region of Sussex 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 Tallamy.
“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 in their flash pattern,” says Tallamy.
There are three characteristics that differentiate firefly species:
- Where the fireflies are located. Some species like to be 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?
If your kids like to catch fireflies and put them in a jar, go for it, says Tallamy, as long as you punch some holes in the lid and release the fireflies after a few hours. Fireflies are beneficial insects; in their larval form they feed on garden and crop pests.
Article by Margo McDonough
The article can also be viewed online on UDaily.