Fireflies Decline as Light Pollution Grows | WYPR

Fireflies Decline as Light Pollution Grows

Aug 4, 2016

  There is a growing movement to measure the worth of nature by quantifying its economic value.  Trees, for example, provide billions of dollars in "ecosystem services" by producing oxygen for humans and absorbing our carbon dioxide pollution.   What, then, is the value of fireflies? I thought about this as I sat on a bench on a summer night, watching a constellation of tiny golden lights wink and wander over the shaggy grasses and darkened trees in the park near my home.

I suppose you could argue that the aesthetic value of fireflies enhances the beauty of the park, and therefore increases the real estate values of the houses around it.

But that’s a stretch. And in fact, real estate development over the last several decades has been causing a decline in firefly populations.


Biologists who study the 150 species of fireflies in the United States have noticed their luminous lives wink out as suburban sprawl has consumed more of the shaggy grasslands and ragged edges of forests where fireflies thrive.

Kathrin Stanger-Hall, a biologist and professor at the University of Georgia, said that firefly populations tend to rise and fall with the amount of rain in a year, breeding more when the conditions are wetter. But over the long term, the trend has been clearly downward.

"There is strong evidence for a decline in fireflies, even though it may not be going from one year to the next, as people might assume," Stanger Hall said.

Marc Branham, who studies fireflies as an associate professor at the University of Florida, said a likely cause that both he and other researchers have identified is a problem that few people think about:  light pollution.  Lightning bugs can’t survive too much light.

"There has been more and more light pollution over the U.S. in the past 20 years," Branham said.  "It’s  pretty easy to look online and see satellite images of the states over the past 20 years and it is astounding how much light pollution there is at night.  And this clearly affects a firefly’s ability to find mates over a given area, if it’s never really dark."

Now, why is this?   Fireflies spend most of their lives as glowing larvae – glow-worms, as they’re called. They live under leaves or bark, preying on slugs and snails and worms.  Then, when its summertime, the they sprout wings and spend about 30 brief but glorious days, flying around, trying to find mates.   In their lower abdomens are organs packed with enzymes luciferase and luciferin – as in Lucifer, the fallen angel of light. These enzymes produce a glow when the bugs allow oxygen into the organs.

The males flash specific patterns – different for each species – to advertise themselves to the females, which generally watch the show from the grass.  When the females see a pattern to their liking, they females respond with bursts of light of their own to let the males know where they are.

Professor Stanger Hall explained why too many lights on houses or in yards interferes with this dance.

"You can imagine if there’s a lot of light around, then those flashes – especially those of the females – are very hard to see,” Stanger Hall said. “And so, some of the mating opportunities are missed, which of course mean less fireflies in the next year."

Everyone agrees that fireflies are a treasure of summer.  But fireflies aren’t valuable because they are valuable to us or provide services to us.   Nature is priceless in itself and should be protected just as human life should be protected, not because of a person’s earning potential, but because life is magical, if fleeting…like the wink of a firefly.