any of certain segmented marine worms of the class Polychaeta (phylum Annelida), including species of the genera Hermodice and Eurythoe. Fireworms produce a stinging sensation if touched. The body of H. carunculata, found in the coral reefs of the Caribbean Sea, is covered with fine, white, brittle bristles that break if touched; they easily become imbedded in human skin and produce a substance that is highly irritating.

The name fireworm is also sometimes applied to the larva of a moth of the insect family Tortricidae (leaf rollers) and to the so-called glowworm—adults and some larvae of the Lampyridae, a family of beetles.