Nine extinct genera and 21 extant species of armadillo have been described, some of which are distinguished by the number of bands on their armor.

Armadillos originated in South America, where they still live today. They are particularly diverse in Paraguay, where 11 species exist. Only the nine-banded armadillo has migrated as far north as the United States.

While armadillos are omnivorous and eat a bit of everything, more than 90% of their diet is made up of insects and their larvae. Armadillos also feed on earthworms, scorpions, spiders, lizards, eggs, fruits, seeds, tubers, fungi, and even the occasional carrion.

They have very poor eyesight, and depend upon their keen sense of smell to hunt.

As nocturnal animals, armadillos perform most activities at night. During the daylight hours, they spend up to 16 hours sleeping, usually in burrows. Armadillos rarely share their burrows with other armadillos, but they do share them with tortoises, snakes, and rats.

A common myth is that armadillos curl up into tight armored balls when threatened by a predator. Only two species--the Brazilian and Southern three-banded armadillos--are capable of this trick. All other armadillo species have too many plates, making this level of flexibility impossible.

Nine-banded armadillos always give birth to identical young formed from the splitting of a single fertilized egg. Among mammals, this is unique to nine-banded and other Dasypus armadillos.

Armadillos sleep away most of their lives, but the pichi (Zaedyus pichiy) or dwarf armadillo takes it a step further by hibernating every winter. Like many hibernating animals, they build up considerable fat reserves before entering their winter burrows, where they remain from May to August. During hibernation, their body temperature drops from its normal value of about 35 °C (95 °F) to just 14 °C (57 °F).

Glyptodonts, a group of gigantic armadillos with spiky club-shaped tails roamed the Americas about 20 million years ago. They were as big as a Volkswagen Beetle, but despite their enormous size, they were grazing herbivores that lacked canine teeth. Archeological evidence suggests that humans hunted these two-ton animals for meat and created shelters from their bony carapaces.

The giant armadillo (Priodontes maximus) grows up to 150 cm (59 in) and weighs up to 54 kg (119 lb), while the pink fairy armadillo (Chlamyphorus truncatus) has a length of only 13 to 15 cm (5-6 in).