Any of the nocturnal luminous beetles of the family Lampyridae, consisting of about 1,900 species that inhabit tropical and temperate regions (including the common glowworm). Adult fireflies are 0.2–1 in. (5–25 mm) long and have light-producing organs on the underside of the abdomen. The soft, flattened, dark-brown or black body is often marked with orange or yellow. Some adult fireflies do not eat; others feed on pollen and nectar. Most fireflies produce short, rhythmic flashes in a pattern that is characteristic of the species and an important mating signal.