The glowing fireflies or glow-worms have always fascinated man. They present a wonderful sight at night. Scientists have been trying to find out from the very beginning how and why fireflies emit light. The firefly is, in fact, a flying worm. Both the male and the female of this worm have wings. In some species, however, females are without wings and are known as glow-worms. They are blackish and their bodies are very soft. They mainly live on the nectar of the flowers. They are found in large number in the tropical humid areas. They emit light in flashes. The light-producing organ is located in the bottom of the abdomen in the rear side and controlled by nerves. It contains two chemicals named ‘luciferin‘ and ‘luciferase‘. Luciferin combines with oxygen to produce light. Luciferase acts as a catalyst for this reaction. It is interesting to note that the light emitted by them produces no heat. Such a process of production of light is called ‘bioluminescence‘. Luciferin is the active luminescent material in the fireflies. The firefly can control the length and rhythm of the flashes from the abdomen. Fireflies usually emit yellow or orange lights. Today scientists can produce such lights in their laboratories. But that can only be done by extracting luciferin and luciferase from the fireflies. Fireflies are usually 4 to 11 millimetres in length. Now one may wonder why a firefly produces light? The first reason is that both the male and the female fireflies emit light to attract each other. The second reason may be that the light so produced may frighten birds and prevent them from attack. Whatever be the reason for this, these fireflies produce a spectacular sight.