Why do Lampyridae insects glow

How and why do fireflies glow?

The phenomenon is particularly common on dry summer nights: suddenly the dark is teeming with small points of light. They are fireflies that either glow continuously or flash at short intervals, depending on the species. Usually it is the females that attract males willing to mate. Since they do not have wings, female fireflies climb trees or plants so that they are better perceived by the flying males. In some species, the males also glow - albeit weaker. Firefly larvae usually also emit light and thus scare off their predators.

The name firefly is actually misleading because the animals are beetles. In addition, they do not glow in the conventional sense, like a light bulb or fire embers, but emit »cold« light without infrared or UV components. They glow according to the same principle as with light-emitting diodes (LEDs) and are based on luminescence, which is generated by a chemical reaction.

Luminescence is created by energetic excitation of electrons, which release the absorbed energy as light. In fireflies, this is done by a molecule called luciferin. The energy required comes from the chemical reaction of luciferin with oxygen, for which, in addition to the enzyme luciferase, the energy carrier adenosine triphosphate (ATP) and magnesium ions are required. The released energy puts the outer electrons in the luciferin in a higher energy state. The excited state is very unstable, however, and the electrons fall back to their old energy level within fractions of a second. They radiate excess energy in the form of photons (light).

During the luciferin-oxygen reaction in the firefly, around 40 percent of the energy absorbed is converted into light, which roughly corresponds to the light output of commercially available LEDs. For comparison: with a light bulb it is only 5 percent, the rest is lost as heat.

By the way, natural scientists use the light reaction of fireflies for research purposes. For example, they combine the luciferase gene with other genes whose activity they want to study. If these are read in the cell, a protein linked to luciferase is created, which generates a light reaction when luciferin and ATP are added. The intensity of the light is directly proportional to the amount of protein. This allows conclusions to be drawn about the activity of the gene in the cell.