The reaction that makes fireflies luminescent has been understood for along time. How they switch themselves on and off, though, is a fairly recent discovery. Find out how fireflies light up, and how they blink off.

Any time you are down on your romantic luck, sitting home depressed on a Friday night in summer and wondering who is more pathetic than you, just look out at the twinkling of the fireflies. They're beautiful, ethereal, and so desperate for a date that they'll light up their own asses, and expend a lot of energy doing it.

Entomologists take pains to explain how light-efficient bioluminescent fireflies are, giving off a vast percentage of the energy they create as light, while light bulbs always produce more heat than light.


The key to lighting up a firefly's life is luciferase, an enzyme, and its tag-team buddy, luciferin, the molecule upon which luciferase enzyme acts. (I had wondered, for a while, about scientists who had looked at the beauty of fireflies in a field or on a tree, and had apparently started humming A Night On Bald Mountain. It turns out, though, that ‘Lucifer' means ‘light-bringer' in Latin, so now I wonder about the people who named the devil instead of the scientists who named the enzyme. Light bringer is pretty good PR. I'd have given the Latin name for 'jerk who really sucks and got caught picking his nose and eating it once.' Its probably shorter in Latin.) Mix in some calcium, and a little adenosine triphosphate (ATP), which is a high energy molecule produced by a cell's mitochondria as a way to power the cell, and you've got a mix that's ready to light up the moment it's exposed to oxygen.

It was the oxygen that mystified scientists for long, long time. Not the presence of it. It was known that oxygen was needed to make the bioluminescence work and that insects took in oxygen. The trouble was, they don't take oxygen in the way people do. It doesn't enter the body through one hole on the face, travel down to the lungs, and get into the bloodstream. Instead it comes in through a number of different tubes on the insect's body.


Insects can't control this oxygen movement precisely. And yet the flashing of their lights is very precise. So the question was how do they manipulate the oxygen exposure fast enough to flash their headlights?

The answer was, they didn't. The controlled the production of another gas, nitric oxide.

The mitochondria, as mentioned above, are the energy generators for the cell. They do this by several different processes, one of which involves taking in oxygen and using it to produce ATP.

Mitochondria are oxygen hungry, but nitric oxide binds to them and makes them stop slurping up oxygen. This leaves the oxygen free to power the bioluminescence. Nitric oxide is not a long-lasting gas. It needs to be continually produced in order to be present in the cell. Once the firefly stops cranking out the nitric oxide, the mitochondria start snapping up oxygen again. There's no oxygen left to start the reaction, and the firefly is left alone in the dark.

Via Scientific American, and times two.

Top image by Judd Patterson.