Armadillidium vulgare, may reach a length of 18 millimetres (0.71 in), and is capable of rolling into a ball when disturbed; this ability, along with its general appearance, gives it the name pill-bug and also creates the potential for confusion with pill millipedes such as Glomeris marginata. It can be distinguished from Armadillidium nasatum and Armadillidium depressum, the only other British species in the genus, by the gap that A. nasatum and A. depressum leave when rolling into a ball; A. vulgare does not leave such a gap
Because of their unusual yet non-threatening appearance, some Armadillidium vulgare are kept as pets in areas throughout the U.S., typically among children. Among adults, they are often seen as unwanted (but essentially harmless) home pests. Keeping a pet pill bug requires a very moist habitat with limited light and lots of decaying plant matter. They can often live up to three years.