Millipedes are arthropods of the class Diplopoda, meaning double foot. Millipedes possess elongated, segmented bodies with two leg pairs per segment. These arthropods are detritivores that feed on decomposing organic material.
Millipedes have long bodies with short antennae and short legs that are vertically in line with their bodies. This compact body shape enables them to plow through soil and detritus. Most millipedes are largely black, dark brown or grey with bolder shades of red, purple or yellow on their segments and legs. Small holes, or spiracles, on each segment allow them to breathe; millipede spiracles are most efficient in moist environments.
Millipedes inhabit nearly every habitat that includes dark, moist areas. They are commonly found under logs, in leaf litter and in compost. These areas provide a rich supply of decaying organic material – a millipede's primary food source. As detritivores, millipedes help to break down nutrients such as nitrogen and return them to the soil.
Millipedes are not capable of biting in defense. Instead, they cope with threats by curling into a ball and secreting toxic or unpalatable substances through their exoskeletons. The secretions of a few species contain cyanide and several tropical millipedes can even project toxin at a predator's eyes.
Millipedes are often confused with centipedes because of their overall shape and number of legs. However, millipedes always have two leg pairs per segment, while centipedes only have one. Further, centipedes are venomous and capable of delivering a sometimes painful bite.