Two types of insects light up: those commonly referred to as fireflies and lightning beetles. Fireflies and lightning beetles are found primarily in humid parts of the world and have evolved light organs as a strategy for preserving the species.
Fireflies are actually a type of beetle in the family Lampyridae, with species numbering in the hundreds worldwide. Fireflies are present throughout most of the U.S. but are most prevalent in areas with high humidity. Some fireflies, such as those found in California, do not light up.
Lightning beetles are related to fireflies and belong to the family Phengodidae. Only female lightning beetles and their larva actually light up. Adult females are commonly referred to as glow worms as they stay in a worm-like form resembling larva (called larviform) even as they grow to an adult size. While most lightning beetles emit yellow light, some emit blue, red or a mixture.
Insects light up using oxygen as a catalyst to mix chemicals--calcium, adenosine triphosphate, luciferin and luciferase—present in their light-producing organs, a process known as bioluminescence. Fireflies control light by opening and closing tubes to let in oxygen, whereas lightning beetles constantly emit light. The flashes emitted by fireflies and lightning beetles attract mates and warn predators of these insect families’ characteristically bad taste.