It is a terrestrial crustacean possessing a rigid, segmented exoskeleton similar to the armor of an armadillo, and fourteen jointed limbs. When alarmed, pill bugs have the ability to roll up into a tight ball as a defense tactic against predators.
They require moisture to breathe with their gills, and are usually found in damp, dark places, like under rocks and logs. Pillbugs are nocturnal and feed on dead plant matter.
Other terrestrial crustaceans that can be confused with Armadillidium in both appearance and name are the genuses Porcellio, Philoscia, and Trichoniscus. These arthropods have a flatter profile, and are incapable of rolling up into a ball. Both groups tend to hang out in the same places, which probably led to the shared common names.