The light that comes every day from the sun provides almost all energy sustaining life on Earth. Anyway, many organisms live in darkness. For some of them darkness is the only choice, as they evolved in habitats where light cannot penetrate, i.e. animals living on the seabed. Also mammals are a good example of how nocturnal habits are common: all bats, the most part of both Mustelids and small rodents, 20% of Primates and 80% of Marsupial are nocturnal, while many other Mammals are active both during day and night. For other organisms, such as the ones that live at the bottom of sea or lakes, darkness is a natural condition. Bacteria, microalgae, Coelenterata, Molluscs, Fishes… the list of bioluminescent organisms is long.
Even among insects many species have crepuscular or nocturnal habits, but darkness poses problems in communicating, so in order to solve those problems several strategies have been adopted as a result of evolution, including bioluminescence.
Actually, among terrestrial invertebrates the ability to emit light mainly belongs to insects: fireflies, click beetles (Elateridae), Collembolans and some dipteran species (Tyler, 2004).
Fireflies emit a light whose frequencies belong to visible spectrum (Booth et al., 2004; De Cock, 2004). Light is produced by special organs consisting of cells provided with many mithocondrions and a molecule(luciferin) whose oxidation (catalyzed by the enzyme luciferase) generates bioluminescence. This process consumes a lot of chemical energy released by ATP, the “energy coin” of cells. Light release can be continuous (i.e. Lampyris adult females) or flashing (Luciola adult males). In the latter case nitrogen monoxide (NO) is involved in the process. The mechanism of light generation by fireflies is a matter of great interest for researchers, because of its energy performance of a muchhigher standard than the one for the generation of artificial light. In addition, genes involved in firefly bioluminescence have been sequenced and cloned to be used for diagnostic purposes.