Fireflies: nature’s light show

The fireworks of the Fourth of July will burst in a crescendo of color in the sky while crowds “ooh!” and “aah!”

There will be another light show, too — a quieter and less boisterous spectacle. You might want to check this one out. It will be performed nightly, for free, throughout July.

This “lite” light show is sponsored by nature and performed flawlessly by fireflies. Generations of Midwesterners have seen the performance over and over, yet still marvel at the spectacle.

How do fireflies create their thousand points of light, you might wonder. Why do they blink in the first place? If I put one in a jar, what should I feed it? And where do they go after disappearing in August?

Scientists have asked these questions, too, and discovered answers to some — but not all — questions about fireflies.

First, a firefly primer. Also known as lightning bugs, fireflies are neither bugs nor flies. They are beetles in the family Lampyridae, which is Greek for “shining ones.” In our area, there are more than four fab beetle species in this family. Instead of names like John or George or Paul or Ringo, they have names like Photuris, Photinus, Pyractomena, and Pyropyga.

Worldwide, there are approximately 2,000 bioluminescent species. The largest and brightest bioluminescent beetles are in the Click Beetle family, ranging from the southwestern tip of the United States to Brazil. The champion genus Pyrophorus, or “fire-bearer,” has the greatest surface brightness of all insects.

In some Indian cultures, women adorn their hair with these shining beetles. Others in South America attach bright beetles to their toes to light their path through dark forests. We are more likely to put fireflies in jars to enjoy their glow lights than attach them to our toes or wear them as jewelry.

The question of how bioluminescence occurs has been piqued the curiosity of laymen and scientists for years. Research has revealed that light is produced at the end of the firefly’s body in a photic, or light-producing, organ. Some entomologists make it simple and call this a lantern. You can see the lantern if you hold a firefly gently and wait for it to blink. See those segments at the end of the insect’s abdomen? This is the business part of the firefly where the important part of life happens.

A pigment called luciferin, an enzyme known as luciferase, a chemical compound called ATP, and oxygen react together in the lantern. When this reaction occurs, it’s as if the insects say “Let there be light!” Then, there is.

The light produced by fireflies and other bioluminescent species is, as some would say, way cool. And it literally is. A firefly’s lantern has an efficiency rating of 90 percent and loses barely any energy as heat. This far surpasses our most energy-efficient household appliances. Light technology has produced LED bulbs which emit cooler light and are more energy efficient than incandescent bulbs, but we have not yet achieved the energy efficiency of a firefly.

Why fireflies create this light is a good question with a good answer. They do it for love. The flashy males blink to woo demure females who are watching from the grass. As the males flirtatiously flash from above, the females must discern who’s signaling. They can detect the species-specific pattern and color of flashes. If a female sees the right guy, she flashes a come-hither signal back to him. If all goes well, they mate — and voila! The female produces eggs. Buried in the ground, the eggs will mature into larvae (sometimes called glow worms), then metamorphose into pupae, and many months later become next year’s adults.

The adults have only one job in the summer, and that is to procreate. In other words, these blinking beacons of passion are all about courtship and mating. In some species of fireflies, adults lack mouthparts and don’t even eat. (This answers the question of what to feed them in a jar — not to worry if they don’t have mouths. Just be sure to release them unharmed.) Adult fireflies only need to find a mate and successfully produce offspring. Fait accompli and it’s the end of the line for the adult firefly.

Fireflies epitomize summer evenings and foster fond memories. After the grand finale of the fireworks in town tonight, look out into a nearby field and watch nature’s own fireworks. Join the kids and catch one. Bask in the tiny glow. You will learn that you can still marvel, and wonder, and delight in life’s simple pleasures.

Ÿ Valerie Blaine is a naturalist with the Forest Preserve District of Kane County. You may reach her at blainevalerie@kaneforest.com.