Fireflies: How and why they light up

How fireflies glow: In essence, a chemical reaction in the beetle’s abdomen gives it its bioluminescence. Image via Cathy Keifer/ Shutterstock.com.

Whether you call them lightning bugs or fireflies, these beetles are a sign of summer. Indeed, you’re most likely to see them in warm weather, when rainfall has been plentiful. Many a child has spent a summer evening chasing them. And, with this in mind, maybe you’ve wondered: Why do fireflies light up? And how do they do it?

How fireflies light up

First, let’s talk about the how. The light of a firefly is a chemical reaction caused by an organic compound – luciferin – in their abdomens. As air rushes into a firefly’s abdomen, it reacts with the luciferin. Consequently, it causes a chemical reaction that gives off the firefly’s familiar glow. This light is sometimes called cold light because it generates so little heat.

According to Firefly.org:

Scientifically, fireflies are classified under Lampyridae, a family of insects within the beetle order Coleoptera, or winged beetles. There are estimated to be 2000+ firefly species spread across temperate and tropical zones all over the world.

In addition, fireflies can regulate the airflow into their abdomens to create a pulsating pattern.

Why fireflies light up

First, fireflies light up for safety. 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 the flavor. In fact, they eat so many fireflies that they themselves begin to glow.

Second, fireflies light up for romance. Male fireflies’ light signals their desire for mates. Also, willing females attract males with flashes of their own.

Lastly, fireflies light up to attract dinner. While each firefly species has its own pattern of flashing, some females imitate the patterns of other species. As a result, males land next to them, only to be eaten alive.

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

Photos from the EarthSky community

View at EarthSky Community Photos. | Matthew Chin in Sha Lo Tung, Hong Kong, captured fireflies and star trails in one photo on August 29, 2017. Matthew wrote: “With limited places, we can see vast number of fireflies. I tried to have the light trails of the little fireflies and the light of stars in one photo.” Thank you, Matthew!

Fireflies via Matt Pollock in upstate New York.

Here, star clusters Messier 6 and 7 shine near Scorpius’ stinger stars, Shaula and Lesath, while fireflies dance in the foreground on a summer night in Yellowwood Lake, Indiana. Image via Zolt Levay.

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

Here’s a 30-second exposure from astrophotographer Tom Wildoner. In fact, astrophotographers often capture fireflies when trying to photograph the night sky.

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

Fireflies via Fiona M. Donnelly in Smiths Falls, Ontario.

Fireflies and star trails via Michael A. Rosinski.

Did you ever do this? Image via Flickr user jamelah e.

Bottom line: Fireflies – aka lightning bugs – light up because of a chemical reaction between an organic compound in the fireflies’ abdomens – called luciferin – and the air.

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