Phengodidae is a family of glow-worm beetles. Their larvae are also glow-worms.

The family occurs only in the New World, and has about 30 genera. Both the females and larvae are bioluminescent: they have organs that can produce light. This family is different from the fireflies (family Lampyridae).

The larvae and the females (which keep their larval form) are predators. They feed on millipedes and other animals they find in the soil and litter. Males are winged. They are attracted to lights at night. They are probably short-lived and do not feed at all. In some species, adult males can also produce light. Females have organs that produce a green or yellow light on their trunks. Some of them (called railroad worms) also have such an organ in front, which can produce a red light.