The peculiar armadillo's strong and flexible shell is unlike the exterior of any other animal on the planet. They have to move quickly on land, so their shells cannot impede their movement, and they must be light and flexible. Armadillos have thousands of thin, bony plates that develop from within the skin to form shells that protect their bodies yet still allow them to burrow, hunt and even swim.
Meet the Family
Twenty-one living armadillo species, inhabiting North, Central and South America, form taxonomic family Dasypodidae. Sloths and anteaters combine with the armadillos to form the group Xenarthra, which also contains extinct species such as giant ground sloths and animals called glyptodonts. In spite of broadly similar morphology, biology and diet, armadillos are diverse; members of the smallest species, pink fairy armadillos (Chlamyphorus truncatus), weigh less than a quarter pound, while the largest, giant armadillos (Priodontes maximus), sometimes exceed 100 pounds. The only North American armadillos, nine-banded armadillos (Dasypus novemcinctus) are born weighing about 4 ounces but reach about 12 to 14 pounds at maturity.
Unlike some other animals with protective shells, armadillos are nimble. That's an important component of their lifestyle. To get the best of both worlds, armadillos have evolved thin but strong bony plates. Embedded within the skin, the bony plates are called osteoderms. The thickness of the shell varies between the species, but in no case is the shell thick; nine-banded armadillo shells are roughly one-tenth of an inch thick. Even though the bones are very thin, the shell can account for up to 15 percent of an armadillo's weight.
Defending Themselves from Prey
Though the shell likely evolved for defensive purposes, it may provide protection against abrasion, which occurs as a byproduct of their subterranean, tunneling lifestyle. Additionally, the thick bony plates may protect the armadillos from biting or stinging prey. While many armadillos are omnivores and prey generalists that consume a wide variety of plants and prey, some species primarily consume ants.
When Armor Fails
Armadillos can’t rely solely on their shell to protect them, so they dig deep burrows in which they can hide, sleep, mate and raise young. In some species, a single large chamber connects to six or more escape shafts. Some species have evolved additional behavioral tactics as well: Hairy armadillos (Chaetophractus nationican) snort at perceived predators, while nine-banded armadillos can leap several feet into the air to evade predators. Nine-banded armadillos will also play dead if a predator captures them.
- Animal Diversity Web: Dasypodidae
- Animal Diversity Web: Xenarthrans
- Journal of the Mechanical Behavior of Biomedical Materials: Armadillo Armor: Mechanical Testing and Micro-Structural Evaluation
- The Anteater, Sloth and Armadillo Specialist Group: Species
- University of California, Berkeley: Introduction to the Xenarthra
- Tom Brakefield/Stockbyte/Getty Images