Millipedes have hard, cord-like bodies made up of multiple segments; each segment has a pair of legs. Because of their many pairs of closely arranged legs, millipedes tend to move slowly, with their legs pushing in a wave-like pattern. When alarmed, millipedes coil up in a tight spiral shape. Size varies greatly by species, with the smallest millipedes measuring about 2 cm in length. While tropical millipedes may measure as long as 30 cm, most Canadian millipede species only reach a length of about 8 cm. Most millipedes are entirely black, though some species may appear dark brown or reddish. They have short but visible antennae made up of 7 segments.

Millipedes are ground-dwelling arthropods that live outdoors and thrive in dark habitats with plenty of moisture. Known to feed on decaying plant matter, millipedes often reside directly within sources of food, like piles of leaf litter or rotting logs. The arthropods also commonly burrow in areas where soil stays moist, like under rocks or piles of mulch.