The firefly is a beetle of the class Insecta that emits a flashing greenish or yellowish light from the underside of its abdomen. The firefly's light is not accompanied by heat. Fireflies, also called lightning bugs, have small, slender, soft, yellow-and-black bodies.
   The light results when two chemicals manufactured by the firefly are combined. One chemical, called luciferin, is activated by another, an enzyme called luciferase. Zoologists think that the purpose of the adult firefly's light is to enable males and females to locate each other in the dark. Not only adults but also the wormlike larvae and sometimes even the eggs can emit light.
The females of  some European fireflies are wingless.They resemble the wormlike larvae in appearance and give off more light that the males. They are often known as glowworms. Fireflies fly at night and remain hidden during the day. Tropical fireflies of Mexico, the West Indies, and South America are larger than those of the temperate regions.