It’s a balmy June evening. The air is so thick and damp you can barely breathe. You sit, lazing in the relative cool of the evening, watching the fairy lights twinkle across the expanse of your long back lawn. One soft green light blinks, then another. Fireflies. Lightning bugs. Your five-year-old run-up, “See! I caught one!” You pry open his little hand and inside, you find the mashed remains of the once beautiful creature which had been giving you so much pleasure.
“What makes fireflies light?” the little tyke asks while you wipe the glowing detritus off his palm.
Fireflies are insects that make light through a process which is called “bioluminescence.” Bioluminescence, literally “life glow” is any light that is made by a living creature. It is commonly found in animals and plants which live partial or total darkness.
Some plant denizens of caves make the light as do many of the fish and invertebrates which inhabit our deepest oceans. Most of them use the same process to make that light. In fact, the glow sticks that we buy in stores and the glowing necklaces bought at parades and amusement parks also use basically the same process.
Bioluminescence is made through a chemical reaction. In an animal, this takes place in a particular part of the animal’s body. In the case of the firefly, it is the tail. There are two chemical components, luciferin, and luciferase.
The names of these chemicals may make some people uncomfortable because of their similarity to Lucifer, one of Christianity’s names for Satan. However, this discomfort is not warranted, according to the Dictionary web site, Lucifer is from the Middle English for “light-bringer.” It is perfectly reasonable that the components that make bioluminescence should be named after light.
Luciferin is the main, and largest by volume, an ingredient in the chemical reaction. It is a protein that is manufactured by the animal’s body. It is a protein, just like the proteins that you eat in foods like meat and fish and the same kind of chemical that makes up your muscles. And like all proteins, it needs a “helper” in order for the firefly’s body to be able to break it down.
This helper is called an “enzyme.” The enzyme in this reaction is luciferase (most proteins have this in/as name relationship). Luciferase aids in the oxidation of luciferin, producing a bluish-green light. Unlike most oxidation or burning, reactions, the reaction is extremely efficient and produces almost no heat as a by-product.
But why do fireflies light? The reason is simple: sex. Fireflies light to attract a mate. The males fly around flashing, looking for a mate, and the females tend to stay still, flashing in encouragement from their hiding places. Each species of firefly has a particular pattern and rate of flash.
In fact, some species of female fireflies imitate the flash pattern of another species and when the male of the imitated species lands to mate, the female eats him. What a way to get a meal!