Why do millipedes curl into a coil when threatened?

Millipedes are slow-moving detritivores that rely on defense rather than speed. When threatened, many species roll into a tight coil, exposing hard outer surfaces and protecting delicate body parts. This posture also helps trap or spread chemical secretions that can deter ants, birds and other predators. Some millipedes release compounds such as benzoquinones, which can be irritating to enemies. Their defensive behavior is a classic example of how non-aggressive animals survive in predator-rich environments.