Fireflies: Suns of the Terrestrial Night

In the dry summer field at nightfall,
fireflies rise like sparks.
Imagine the presence of ghosts
flickering, the ghosts of young friends,
your father nearest in the distance.

–Marilyn Kallet

For me, one of the greatest parts about summer is the emergence of fireflies. For a month or two each year, I love to watch morse-code storms lift from inverted grass-clouds. I know they’re talking to each other, but sometimes I can’t help but wonder what secret signals are hidden in the silent concert.

Of course, these beings have other common names, including lightning bugs and glowworms. Despite the “fly” and “worm” nomenclatures, fireflies are actually a form of beetle. The aptly-named family of the insects is Lampyridae. It includes more than 2,000 species!

Photograph by Medford Taylor, Nat Geo Image Collection

This family of beetles is, obviously, famous for bioluminescence, the production of light from a living organism. The fireworks are “cold light.” It produces almost no heat and has no infrared or ultraviolent content. According to National Geographic, fireflies have a “dedicated light organ.” Oxygen intake is mixed with a substance called luciferin, which produces the signals.

Each species of firefly has a unique blink. Scientists are not exactly certain how the insects are able to turn their lights on and off, but they know the process is used for communication and mating. It’s also thought that the bioluminescence serves as a type of defense mechanism, telling other organisms that the beetles taste yucky.

The light clocks in with wavelengths of 510-670 nanometers, making the visible light yellow, green, or pale red. There’s even a form of firefly known as the “blue ghost,” that seemingly emits blue hues, though their light is technically green. It’s perceived as blue due to something known as the Purkinje effect. To cameras, their light displays as green.

"Firefly illuminating blades of grass and due drops" by Radim Schreiber

Several species of fireflies are also known for synchronization. Their flashes tend to line up in large groups. 

In the Philippines, along the river in the town of Donsol, is a species of synchronous fireflies, for which one can take a night cruise to witness. In the United States, Congaree National Park and Great Smoky Mountains National Park are home to famous flocks of fireflies blinking in unison.

Each June, thousands of people travel to the Smokies to witness the displays.

Interestingly, while all species of fireflies feature bioluminescence during their larval stages, not all of them continue to light up as adults. Some species are “dark” and use pheromones to attract mates instead of blinking.

But those species that do create fireworks are some of the most magical inhabitants of our world. The difficulties of documenting nighttime critters often mean our own eyes are by far the best way to view their shows. But when skilled photographers and videographers do come up with something the results are usually enchanting. Time-lapse technology can allow the fireflies to paint abstract canvasses.

Photographer Radim Schreiber chronicles these insects for his project, called Firefly Experience. Here’s a taste of his fantastic work:

Fireflies light up a forest
The comet NEOWISE soars above a field of fireflies

Unfortunately, the number of fireflies around the world is declining. Loss of grassy habitat, light pollution, and pesticide use have combined to take a toll on their populations. Hopefully, we can conserve these enigmatic insects. Everyday people can chip in. The National Wildlife Federation even provides certification for yards!

For the time being, experience them like the natural wonder they are.

I have not yet made it to the Smokies to take in Photinus carolinus, the synchronous species of the southeastern United States, but I have seen enough of the organic aurora borealis to know I’m in love.

Further Reading and Exploration

Firefly Experience

11 Cool Things You Never Knew about Fireflies – Scientific American

Fireflies – National Geographic

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