Nature’s Night Light
Sometimes known as the sea-firefly, Vargula hilgendorfii is a species of ostracod crustacean that only inhabits coastal waters off Japan. It is a nocturnal creature that rarely grows longer than 3 millimetres, with a beautiful transparent shell—but it’s best known for its bioluminescence. When disturbed, it secretes a luminous blue substance through a process similar to many other bioluminescent creatures: a chemical reaction of the substrate luciferin and the enzyme luciferase. The maximum wavelength of its light depends on the pH and the salinity of the water, and varies between 448 and 463 nanometres—meaning that the light is coloured various shades of blue. In World War II, the Japanese collected these creatures and crushed them in sand and water to produce their blue luminescence, which ingeniously served as light for soldiers to read maps and messages at night.