Glowworm or glow-worm is the common name for various groups of insect larvae and adult larviform females that glow through bioluminescence.
They include the European common glow-worm and other members of the Lampyridae, but bioluminescence also occurs in the families Elateridae, Phengodidae and Rhagophthalmidae among beetles; as well as members of the genera Arachnocampa, Keroplatus and Orfelia among keroplatid fungus gnats.
Their light may be emitted as flashes or as a constant glow, and usually range in colour from green, yellow, to orange.
Phylogenetic analyses have indicated that bioluminescence may have a single evolutionary origin among the families Lampyridae, Phengodidae, and Rhagophthalmidae; but is likely to have arisen independently among Elateridae.
Despite the similarities in function and appearance, the bioluminescent systems of the three genera are not homologous and are believed to have evolved separately.