millipede, elongated arthropod having many body segments and pairs of legs. Millipedes, sometimes termed thousand-legged worms, have two pairs of legs on each body segment except the first few and the last. Females in one Californian species, Illacme plenipes, typically have more 650 legs, but are only 1.3 in. (33 mm) long; the leggiest ever found (1926) had 750. The millipede body is nearly circular in cross section. Most temperate region millipedes are rather small and dull in appearance, but a few tropical species are brightly colored, and some reach 1 ft (30 cm) in length.

Millipedes do not have a poisonous bite, but many protect themselves by offensive odors produced by stink glands; some produce highly irritating compounds that can injure the skin or eyes of attackers; and some can roll up into a ball or spiral for protection. They are widely distributed in temperate and warmer regions, living in surface litter, under stones or logs, and in relatively humid surroundings. They feed mostly on decaying vegetation, although some will consume decaying animal food. Some species attack plant roots and cause crop damage.

Centipedes, with which millipedes are often confused, are carnivorous, have a single pair of legs on each segment, and a body that is flat in cross section. Millipedes belong to the phylum Arthropoda, class Diplopoda.

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.

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