Why do lightning bugs glow in the dark?
Do you mean "why" or "how"?
They glow in the dark as part of a
communication system they use to find mates. The female waits and flashes at
flying males. The males flash back and try to find the right species females.
The temporal and spatial pattern of the light flashes confer species
specificity - usually. Biology is a case in exceptions. There is one species
of firefly whose females flash in many different ways to attract other species
males. When the wrong species male arrives, he is eaten! Gives new meaning
to not believing everything you see.
As to how they glow: they use two
chemicals called luciferin and luciferase. The luciferase is an enzyme, a
protein catalyst which is not consumed in its reaction with luciferin. The
luciferin changes chemically and gives off light. Whenever an electron drops
an energy level (a quantum leap) in a molecule, it gives off a photon of
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Update: June 2012