How does a firefly emit light?

    Firefly also known as lightning bug is the common name for about 100 species of insects found throughout the tropical and temperate regions. Fireflies are soft-bodied insects measuring` from a few centimetres to about a few tens of centimetres. They have generally dark brown sheath-like front wings covering the flying wings at rest, yellow or orange markings and luminescent glands located on the underside of the rear abdominal segment. Both sexes emit intermittent light signals often seen in meadows on late-spring and summer nights, to attract mates. The luminescent larvae and females of some species are also called glowworm. The firefly emits light by allowing oxygen, breathed through its abdominal tracheae, to combine with a substance called luciferins. The fly also controls the timing and duration of the flashes, for example, to attract its mates. The unique characteristic of the fly is that it emits light without producing heat.

            The process of emission of ‘cold’ light by living beings by various enzymatic reactions is termed bioluminescence or chemiluminescence. The glowworms, Lampyris noctiluca, are bioluminescent insects. The light produced may either be extracellular (outside the cells) or intracellular (inside the cells). Luciferin, a substance present in glowworms gets oxidized in the presence of an enzyme called luciferases to give light and carbon dioxide. Emitted light may be blue, green, yellow, red, orange or a combination of these colours.

            The intensity of the colour also differs among various animals. It is said that when 10 Phyrophorus noctilucus are kept in a glass bulb, one can read printed pages comfortably.

            The animals use this cold light to procure food, to escape from predators, as warning signal and as mating signal. During photosynthesis radiant energy (light) is converted into chemical energy (starch) by plants. But during bioluminescence the chemical energy in the body is converted into radiant energy, without raising the temperature in the process.

            In glowworms, a combination of adenosine tri phosphate (ATP) and oxidative energy is used in a set of reactions that convert chemical energy into light energy. Generation of light flash requires activation of luciferins by an enzymatic reaction with ATP in which a pyrophosphate cleavage of ATP occurs to form luciferyl adenylate. This compound is then acted upon by molecular oxygen luciferases to bring about the oxidative decarboxylation of luciferins to yield oxyluciferin. The intermediate step of this reaction is accompanied by emission of light. Luciferin is then regenerated from oxyluciferin subsequently.