Found this long, dark worm-like thing coiled up on my basement floor. It has a hard shell and tons of tiny legs. Is it harmless or something to worry about?

Encouraging curiosity about nature can foster a healthy respect for the environment.
If you have pets that might be prone to investigating or playing with millipedes, ensure they have plenty of toys and activities to distract them. Keeping your living space dry and clean will also reduce the chances of millipedes wandering into areas frequented by children and pets.