The word "millipede" means “one thousand legs." Contrary to the meaning of the name, flat millipedes have no more than a hundred legs. The millipedes recorded with most number of legs have fewer than eight hundred.

These arthropods are colored brownish-black or may be mixed with shades of red, orange or brown. Millipedes can be flattened or cylindrical (wormlike) elongated animals. They have, at most, two pairs of legs in each segments after the first three body segments. The first three segments only have one pair of legs. The antennae of millipedes are short. Their head is rounded with no poison jaws and their antennae are seven-segmented. The millipedes curl up into a tight "C" shape, remaining motionless when they are touched. Length sizes ranges from 1/2 to 1-1/4 inches long depending on the species. The longest recorded millipede is the Archispir ostreptus gigas which can grow up to 8-11 inches.

These millipedes crawl at a snail's pace. For their protection, they have glands secreting an unpleasant odor when they are in danger. Millipedes neither bite nor sting.

The lifespan of millipedes can reach up to seven years. When they reach adulthood, they overwinter and then lay their eggs in the soil either singly or in small groups. Fertilization among millipedes is internal. They have the ability to lay twenty up to three hundred eggs. These eggs will hatch after a few weeks. It will then reach adulthood when autumn arrives. Sexual maturity among millipedes varies. Some would reach it by their second year, while other millipedes can spend up to four or five years stuck in the larval stage.