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Fireflies: Nature’s Own Celebration of Summer

By Amy Renfranz (

Article Published: Jul. 3, 2013 | Modified: Jul. 3, 2013
Fireflies: Nature’s Own Celebration of Summer

Each firefly species has its own specific light pattern.

Photo submitted

Could there be a creature more synonymous with “summer” than the firefly?

I do not think so.

With every cool, damp Appalachian evening, there is the firefly.

With every afternoon picnic that lasted into the night, there is the firefly.

For any curious kid with a net and a Mason jar, there is the firefly.

Sometimes numbering in the thousands, they can light up an entire field and fill a person with awe and admiration. I have seen this spectacle a few times and would include those evenings as some of my most unforgettable experiences in the outdoors.

Just what are those fireflies up to? This week’s reader question aims to shed some light on the matter.

I have been vacationing in the High Country for many years. This is my 40th summer here. One of my favorite things is the fireflies that come out every July. When I was a kid, I would catch them. Now, I just watch. And wonder. What are they doing? Why do they have a light, and how does it work? — Charlie, New York

It seems that you and I have at least two things in common, Charlie: curiosity and the propensity to sit and watch things.

The next time you are out at night, capture a firefly. Gently hold it in your fingers and look at its abdomen. Near the tail end, the firefly’s external skeleton is transparent. If you look closely, you can see the pale yellow light-producing organs within its body.

Within the organs are thousands of cells called photocytes, which contain the chemicals, luciferin and luciferase. There are also breathing tubes passing through the photocytes. These tubes open to the outside via pores called spiracles.

As oxygen from the breathing tubes comes into contact with the chemicals within the photocytes, a chemical reaction occurs, which produces the light. Since it is a naturally produced light, it is called “bioluminescence.”

The firefly’s light is a “cold light,” which means that there is hardly any heat produced as a side effect. In contrast, 90 percent of a light bulb’s output is wasted as heat.

Depending on the species (there are 130 species in North America), a firefly’s light can be yellow, green, blue or orange. Each species also has its own specific flash pattern.

The males fly around emitting their species’ light pattern, while the females wait in the grass. If a female spots the right light pattern, she will then respond with her own beacon.

She is essentially calling her male in. When he lands, they will mate.

Some females have been known to mimic the responses of other species to fool the males. Once the poor sap lands, she will eat him.

Every animal on earth has found some way to attract mates. For the firefly, light is the main attraction. And it is a very proficient way to find a mate in a world full of possible predators.

For only 90 minutes after each sunset during July, the fireflies expose themselves to the world by revealing their light within. Luckily for us, we can sit and watch it happen.

Amy Renfranz is a North Carolina certified environmental educator, certified interpretive guide, and a Yellowstone Association Institute certified naturalist. Have a question? Email Amy at ( or visit Dear Naturalist’s Facebook page.

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