Lampyrid insects - the Lampyridae - are a family of insects in the beetle order Coleoptera. They are winged beetles, and commonly called fireflies or lightning bugs for their conspicuous use of bioluminescence during twilight to attract mates or prey. Bioluminescence is the production and emission of light by a living organism. It is a form of chemiluminescence. Bioluminescence occurs widely in marine vertebrates and invertebrates, as well as in some fungi, microorganisms including some bioluminescent bacteria and terrestrial invertebrates such as fireflies and glow-worms. In some animals, the light is produced by symbiotic organisms such as Vibrio bacteria.

More Info: en.wikipedia.org