Centipedes (class Chilopoda) always have an uneven number of pairs of walking legs, varying from 15 to more than 171. The true centipedes (order Scolopendromorpha) have 21 or 23 pairs of legs. Common house centipedes (Scutigera coleoptrato) have 15 pairs of legs. Centipedes are all carnivorous and feed mainly on insects. Millipedes (class Diplopoda) have thirty or more pairs of legs. They are herbivores, feeding mainly on decaying vegetation.