Millipedes that live outside are found living in or under dark damp places like mulch, landscaping ties, leaf piles, fallen trees, and piles of grass. They are described as scavengers and therefore feed basically on whatever organic materials that they come across- decaying plant materials and sometimes even other dead insects.
Millipedes live happily outside but can be seen migrating in very large numbers after periods of heavy rain or in the late fall when they start to search for warm shelter. They will come in through the gaps found around basement doors and windows and through spaces found in and around vents and ducts. Inside, they hide in dark basements, closets, underneath bathroom and kitchen sinks, and in laundry rooms.
Once inside, millipedes are thought of as nuisance pests. They really cause no harm to people and aren’t known to transmit any diseases. The liquid that they emit can cause small blisters on some people and can be toxic to smaller pets when they come into contact with them.