or lightning bug
Any of the nocturnal luminous 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.