The difference between millipedes and centipedes lies in their leg positioning. Millipedes have two sets of legs per segment. Centipedes, on the other hand, have one set of legs per segment on the body side. Both millipedes and centipedes are venomous, but centipede venom is more potent. Centipede venom is used to kill prey, while millipede venom is used for self-defense. Millipedes mostly eat decomposing plants, while centipedes feast on insects.