by Christy Kohlhaas

Many of us have childhood memories of watching fireflies in the backyard, carefully catching them between our cupped hands, and releasing them back into the night sky. Each summer, we eagerly wait for their return, but not many of us know much about them. What are fireflies?

Where do they come from? What causes them to light up at night, and why?

What are fireflies?

Fireflies (Lampyridae), which are also known by many of us as lightning bugs, are not really flies, but winged beetles. However, unlike other beetles, fireflies belong to a rare group of creatures known as bioluminescent animals. Bioluminescent animals are a fascinating group of creatures that are known for glowing in the dark.

In the evening, many species of fireflies can be identified by the flickering light that they produce in the dark. In the daytime, fireflies can also be identified by their flat, black bodies with wings and red, orange, or yellow markings.

Where do fireflies live?

Around the world, there are about 2,000 known species of fireflies, with about 150 of these living in the United States and Canada alone.

Fireflies prefer to live in forests, fields, meadows, and marshes, although some of them appear in more suburban settings, like our backyards.

Sadly, their numbers are declining, mostly due to habitat loss, including not having healthy ecosystems in which their young (aka larvae) can survive.

How do fireflies light up at night?

Fireflies produce light through a chemical reaction caused by oxygen, calcium, ATP, and luciferin. This chemical reaction, known as bioluminescence, produces cold light, which is a unique type of light that fireflies produce without losing energy or creating heat.

Fireflies, which have a “light organ,” also called a lantern, in their abdomen, control when the light turns “on” and “off” by regulating the flow of oxygen to the cells in the light organ. When oxygen is absent, the light turns “off.” When oxygen is present, the light turns “on.” This “on” and “off” pattern is known as the firefly’s flash pattern.

Most species blink with their own coded pattern. This is one way that fireflies recognize their own kind.

Why do fireflies light up?

When a male firefly is looking for a mate, he will flash his light “on” and “off” to attract the attention of the females. When a female firefly is impressed, she will respond by flashing her light back to the male.

Fireflies also use their lights to warn predators. Although the firefly’s light makes it easy for predators to find, most predators avoid fireflies because of their blood, which is toxic if ingested.

Fun Facts!

• Although most of us know fireflies by their yellow light, some fireflies can also produce green or orange light.
• Most species of fireflies are nocturnal, which is why we often see them lighting up the night sky.
• Sometimes, a group of fireflies coordinate the timing of their flash patterns, which causes all of their lights to turn “on” and “off” at the same time.
• All fireflies can glow as larvae, but not all species of fireflies light up as
• Adult fireflies have a very short lifespan of just a few days to a few weeks.
• The light of the firefly is almost 100% efficient, making it the most energy efficient light in the world.

As you sit outside and enjoy the warm, summer evenings this month, keep your eyes open for fireflies.

Recommended Reading:

We highly recommend this wonderful article by Louisville resident, Dr. Margaret Carriero. You’ll learn more about fireflies and how you can help them.  https://louisville.wildones.org/2023/05/10/fireflies-coming-to-their-rescue-at-home/