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EarthSky // Earth, Science Wire Release Date: Jun 12, 2015

Why do fireflies light up?

Next time you see a firefly, keep in mind that its flickering isn’t just a wonder of the night. It’s also a unique, and sometimes deadly, language of love.

View larger. | Fireflies in northern spring 2015 by Matt Pollock .

View larger. | Fireflies in May 2015 – just as the big 2015 firefly season was getting revved up – by Matt Pollock .

Fireflies are sometimes called lightning bugs. Many a child has spent a summer evening chasing them. And maybe you’ve wondered – how and why are these insects able to light up?

Fiona M. Donnelly in Smiths Falls, Ontario reports a bumper crop of fireflies this year, too. Photo taken June 8, 2015.

Fiona M. Donnelly in Smiths Falls, Ontario reports a bumper crop of fireflies this year, too. Photo taken June 8, 2015.

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The answer is that fireflies contain an organic compound in their abdomens called luciferin. As air rushes into the abdomen, it reacts with the luciferin. A chemical reaction gives off the familiar glow of a firefly. This light is sometimes called “cold light” because it generates so little heat. The firefly can regulate the airflow into the abdomen to create a pulsating pattern.

“Fireflies on top of the wave of grass and overflowing. Biggest firefly show in years.” By Eileen Claffey in Brookline, Massachusetts, June, 2015.

Here's another cool firefly photo from EarthSky Facebook friend Tom Wildoner.  He said it's a 30-second exposure.  Astrophotographers often capture fireflies when trying to photograph the night sky.

Here’s another cool firefly photo from EarthSky Facebook friend Tom Wildoner. He said it’s a 30-second exposure. Astrophotographers often capture fireflies when trying to photograph the night sky.

Some experts think the firefly’s flashy style may warn predators of the insect’s bitter taste. On the other hand, some frogs don’t seem to mind. They eat so many fireflies that they themselves begin to glow. Male fireflies also light up to signal their desire for mates – and willing females attract the males with flashes of their own.

But not all the flashing of fireflies is motivated by romance. While each firefly species has its own pattern of flashing, some females imitate the patterns of other species. Males land next to them – only to be eaten alive.

You can see what looks like trails made by fireflies, via long-exposure photography from EarthSky Facebook friend Jack Fusco Photography. There's also a single meteor in the upper left of this photo. See it? It's straighter than the firefly trails.

Fireflies and star trails from EarthSky Facebook friend Michael A. Rosinski. Michael shot this on June 20, 2012, night of the solstice - shortest night of the year.

So the next time you see a firefly, keep in mind that its flickering isn’t just a wonder of the night. It’s also a unique, and sometimes deadly, language of love.

Bottom line: Why do fireflies light up? It’s because of a chemical reaction between an organic compound in the fireflies’ abdomens – called luciferin – and the air.

Check out the Museum of Science Firefly Watch