More detailed work demonstrates how the fireflies produce their own nitric oxide in cells that line the ends of the air tubes in their lanterns.
Now, a US team has been able to show that the simple molecule nitric oxide (NO) acts as the on-off "button".
It is just one more example of the prominent role played by NO in biochemistry. In humans, the molecule is crucial to the dilation of blood vessels and the signalling that goes on between neurons in the brain.
Its part in assisting men achieve erection has been exploited by the modern impotence drugs like Viagra.
Reacting chemicals
To understand the role NO plays in fireflies, Barry Trimmer, from Tufts University in Medford, Massachusetts, and colleagues studied the insects in tiny custom-designed chambers.
Whenever the fireflies were exposed to nitric oxide they glowed or flashed almost continuously, and they stopped once the nitric oxide was turned off.
More detailed work demonstrates how the fireflies produce their own nitric oxide in cells that line the ends of the air tubes in their lanterns.
The molecule causes oxygen-consuming components on the edge of light-producing cells in the lantern to briefly shut down. This allows oxygen to pass through to the interior of the cells and react with the chemicals luceriferin and luciferase to generate a flash.
When the NO is turned off, the oxygen "gatekeepers" started up again and the light disappears. The whole thing happens in milliseconds.
Short romance
"We knew about the chemistry that makes fireflies light up," Barry Trimmer said, "but we now have the missing piece of the puzzle that explains how they are able to throw the switch on and off."
Many animals, including jellyfish and bacteria, use bioluminescence to communicate. "However," co-researcher and a Tufts University firefly expert Sara Lewis said, "The firefly's talent for producing precisely timed, rapid bursts of light is quite rare."
This ability has allowed fireflies to evolve an elaborate courtship system based on flash communication.
Males blink a certain sequence and hope to see an answering flash from a female. Each of the 200 or so species of firefly have their own signal.
The insects live for two years as larvae, eating worms in the soil, and for just two weeks as adults - enjoying just 14 nights of flying, flashing and courtship. Then it is all over.
"For them, it is a very short, intense time," Lewis said.
The firefly research is published in the journal Science.