Most diverse terrestrial bioluminescent animals

The most diverse terrestrial bioluminescent animals are the beetles (order Coleoptera). More than 3,000 beetle species in at least five different taxonomic families of collectively global distribution are bioluminescent. The vast majority of these are fireflies, contained within the family Lampyridae (which also includes some glow-worm species); many but not all firefly and glow-worm species are bioluminescent. The others occur within the families Elateridae (click beetles), Phengodidae (glow-worm beetles and railroad worms), Rhagophthalmidae (rhagophthalmid glow-worms) and Staphylinidae (rove beetles). In some firefly species, only the larvae are bioluminescent, whereas in others both the larvae and the adults are. The location of light-emitting organs on their bodies can vary between firefly species, and even between the sexes of the same species.

Several species from additional beetle families have been claimed to be bioluminescent in the past, but these claims have not been scientifically substantiated. What has been confirmed, however, is that the so-called railroad worms, i.e., the worm-like larvae and adult females (also worm-like) of phengodid glow-worm beetles belonging to the genus Phrixothrix, are unique among all terrestrial bioluminescent animals by emitting light of two totally different wavelengths. Eleven pairs of light-emitting organs running along most of their thoracic and abdominal segments release greenish-blue light, whereas a single pair of medially sited organs on their head release intense red light (these particular beetles are the only terrestrial bioluminescent organisms known to release intense red light).

The brightest bioluminescence recorded in any animal is that of a click beetle: fire beetles (Pyrophorus noctilucus) can output light with an intensity of 45 milllamberts (as bright as a modern single LED torch). There are two dots on the beetle's head and one on its abdomen, which is only visible when it is flying. The beetle lives in the tropical regions of the Americas.