About 2,100 species of fireflies are found in temperate and tropical climates. Many are in marshes or in wet, wooded areas where their larvae have abundant sources of food. Their larvae emit light and often are called "glowworms" in Eurasia and elsewhere. In the Americas, "glow worm" also refers to the related Phengodidae.
Light production in fireflies is due to a type of chemical reaction called bioluminescence. This process occurs in specialized light-emitting organs, usually on a firefly's lower abdomen.