Any of about 10,000 species of the arthropod class Diplopoda, found worldwide.
Most species live in and eat decaying plant matter. Some injure living plants, and a few are predators and scavengers. Millipedes are 1–11 in. (2.5–28 cm) long and have from 11 to more than 100 diplosomites, double segments formed from the fusion of two segments. The head is legless; the next three segments have one pair of legs each; and the remaining segments have two pairs each. In defense, millipedes do not bite; most species tuck headfirst into a tight coil, and many secrete a pungent, toxic liquid or gas.