The easiest way to tell centipedes and millipedes apart is to count the number of legs per body segment. According to Orkin, centipedes have one pair of legs per body segment, and millipedes have two.
Another way to tell the two apart is to watch them move. Centipedes characteristically move very rapidly. Not only are millipedes much slower, but they also burrow. Diet differs as well. Centipedes are carnivorous, hunting and injecting venom in their prey using maxillipeds, which are modified legs on the first body segment. Most species of millipedes feed on decaying plant matter as well as the roots and leaves of seedling plants. While millipedes don’t sting, they do secrete caustic compounds to ward off predators. Another means of defense is to also curl their bodies into tight coils to take advantage of their tough outer body and protect their more delicate legs.
There are some important ways in which centipedes and millipedes are similar. First, while centipedes rarely bite humans, their venom can cause allergic reactions, especially in people who are sensitive to it. Likewise, millipedes’ defensive secretions can cause mild burns and burning sensations on the skin and in the eyes. Also, both centipedes and millipedes prefer a moist, sheltered outdoor habitat.