Fireflies are truly dazzling to watch; the way that they dance across a dark backdrop, twinkling like stars. But how do they put on this hypnotizing light show? While scientists have understood the chemistry behind their bioluminescence for some time, the physics side of this beautiful phenomenon has been somewhat of a mystery. Now, thanks to a combination of sophisticated imaging techniques, researchers have managed to reveal the fine details behind firefly light flashing for the first time.
Fireflies use blinking light signals as a means of communication. Each firefly species has its own pattern of flashing, which they use to indicate their desire for mates. It’s also thought that the glow could be acting as a warning system to deter predators.
The secret behind this type of light production, which is known as bioluminescence, is a combination of chemicals that react in the presence of oxygen. When oxygen molecules combine with calcium, ATP—the energy currency of the cell—and a chemical called luciferin, light is produced with the assistance of an enzyme called luciferase. This process takes place in light-producing cells, or photocytes, within a light organ called the lantern, which is located in the abdomen. The cells within the lantern, which apparently smells like sweaty feet, are supplied with oxygen by a branching series of successively smaller tubes that are collectively known as the tracheal system.
While this much is known, the precise mechanism of oxygen supply for light flashing eluded scientists. This was because the tracheal system has a complex microscopic geometry that had not been resolved, meaning that scientists couldn’t test any of the proposed mechanisms. To address this gap in our knowledge, an international team of researchers from Switzerland and Taiwan used two cutting-edge imaging techniques to probe the complexity of both the lantern and the tracheal system. These techniques are called synchrotron phase contrast microtomography and transmission X-ray microscopy. These allowed the researchers to peer into individual cells in live fireflies and map out how oxygen is supplied to and distributed within the photocytes.
As described in the journal Physical Review Letters, they found that the amount of oxygen gobbled up by mitochondria—the energy making powerhouses of cells—exceeded the maximum rate of oxygen supply to the photocytes from the tracheal system. Therefore, in order to flash, the insects actually divert oxygen away from the mitochondria, which slows down energy production in the cell. This oxygen is then redirected in order to supply the bioluminescent reaction.
And here are some pretty pictures to remind you how beautiful they are: