Bioluminescence – Living Lights

At recent July 4th fireworks displays, spectators squealed with delight at the annual spectacle that illuminated the night sky. And I’m sure more than a few compared the spectacular pyrotechnics to the subtler displays of fireflies that punctuate backyards, parks, and campgrounds all summer long.

We call these displays “nature’s fireworks.”

Fireflies, or lightning bugs, are neither flies, nor bugs. They are beetles capable of bioluminescence.

The light that fireflies produce is nothing short of amazing. It is cold light, produced biochemically with little energy lost as heat.
Compare that to an incandescent light bulb that gets too hot to touch in just minutes. New LED bulbs are more efficient and produce much less heat, but science still covets a source of cold light.

The bioluminescent organs of fireflies are located on their abdomen. In the cells of the light organs, which are richly supplied oxygen, is a chemical called luciferin.
When luciferin combines with oxygen in the presence of the enzyme luciferase, the chemical reaction releases energy in the form of light.
Reflector cells in the light organs magnify the intensity of the light so that’s it’s impossible to miss nature’s light show on a warm summer evening.

Most local species seem to flash randomly, but each species flashes a distinct Morse code-like pattern.
Males flash, females respond, and then they find each other to mate.
What child has never captured fireflies and studied them inside a used mayonnaise jar?
Some species flash synchronously by the thousands and light up entire forests. The most spectacular of the synchronous species occur in southeast Asia, but they are also known in the Great Smokey Mountains.

Though bioluminescent fireflies are well known, thousands of other species are capable of producing “living light.” Many are restricted to the world’s oceans. Some are even tourist attractions.
A few years ago, my daughter and her husband vacationed in Puerto Rico, and they took a night cruise to see the illuminated waters. Sure enough in the wake of the boat, the water glowed mysteriously. It was a high point of their trip.
In this case, it was tiny microorganisms called dinoflagellates that created the light. Though the biochemical details vary, the process of light production parallels that of fireflies.

The big question is why such tiny organisms would need to produce light at all. The answer is uncertain, but there are two intriguing theories.
One idea is that a pulse of light alarms or disorients predators pursuing the tiny prey. Another possibility is that the light may expose approaching predators to even bigger predators, which then eat the smaller ones.

The ocean around the Antarctic is home to unfathomable numbers of shrimp-like animals called krill.

At two to three inches long, they occur at densities of tens of thousands per cubic meter of water, and they emit burst of blue bioluminescence, perhaps as a means to stay in touch with each other in the dark ocean. The krill eat plankton, and everything from jellyfish and sea birds to fish and baleen whales eat krill.

These krill are the primary food of whales in the south polar oceans, so bioluminescent organisms are an important part of the global food chain.

Some bioluminescent organisms outsource their light-producing duties to luminescent bacteria. The Hawaiian bobtail squid provides these bacteria with a place to live in exchange for a lantern.
The lantern is located on the bottom of the squid, and from below, the squid blends in with the moonlit sky above. Thus the squid gains protection from predators lurking below.

Many tropical fish also use luminous bacteria to create lanterns that can be used for protection, camouflage, and/or communication. Some have lids that cover the light organs.
These fish can turn their headlights on and off and are called flashlight fish.

Though the vast majority of bioluminescent organisms live in oceans, the ones we know best, fireflies, can be seen in our backyards.
Sometimes the most amazing wonders of nature are just outside the back door.

Catskills Fireflies 2012 Photo: https://www.flickr.com/photos/s58y/ / CC BY 2.0