Centipedes and millipedes seem similar, but they have different diets and body structures.
Centipedes are fast-moving carnivores that kill their pray with venomous bites. Their bodies are flat and they have one pair of legs per body segment. Bites are not normally dangerous to humans, but infants and small pets may be more susceptible to centipede venom.
Millipedes are slow-moving insects that eat decaying matter. Their bodies are rounder, and they have two pairs of legs per body segment. Millipedes do not bite, but some species release toxins from glands on their bodies, and this toxin can cause blisters on human skin.
These differences aside, centipedes and millipedes live in similar environments – safe, moist places, like rotting wood, leaf piles, plant mulch, etc. Most cannot survive for more than a few days without these conditions, and so they are not usually found in homes. They are an unsightly garden pest, however, and professional treatments can remove them permanently.