Armadillos are New World placental mammals, recognizable by the bony shell that gives them their Spanish name, meaning “little armored one.” They belong to the superorder Xenarthra, a group that also includes sloths and anteaters, all native to the Americas. With 21 distinct species, armadillos range in size from the tiny pink fairy armadillo to the giant armadillo, inhabiting diverse environments.
Their Natural Armor: Structure and Purpose
The armadillo’s defining feature is its shell, or carapace, made of bone and skin. This armor is composed of bony plates called osteoderms that develop in the skin and are covered by keratinized epidermal scales. The armor is divided into rigid shields over the shoulders and hips, connected by flexible bands that allow for movement.
This segmented design provides protection while retaining mobility, and the shell can account for about 16% of the animal’s body weight. The effectiveness of the armor varies significantly by species. The widespread nine-banded armadillo cannot fully roll into a ball and often escapes predators by fleeing or jumping. Only the South American three-banded armadillos (genus Tolypeutes) can curl completely into a nearly impenetrable sphere.
Unique Reproductive Biology
The reproductive cycle of the nine-banded armadillo (Dasypus novemcinctus) includes monozygotic polyembryony. This process means a single fertilized egg divides multiple times to produce a litter of genetically identical offspring. This is the only reliable manifestation of polyembryony in the entire class Mammalia.
After delayed implantation, the blastocyst develops, splitting into four distinct embryos. A female nine-banded armadillo gives birth to a litter of identical quadruplets of the same sex. Other species, like the seven-banded armadillo, may produce larger litters of identical siblings, sometimes up to twelve. This trait makes them valuable subjects for scientific studies.
Specialized Digging Lifestyle
Armadillos are specialized burrowers, using powerful limbs and sharp claws for both foraging and shelter. Their proficiency at digging has earned them the classification of “ecosystem engineers.” By creating extensive burrow systems, they alter their environment, which benefits many other species.
These burrows provide shelter from predators and serve as thermal refuges from extreme temperatures for a variety of vertebrates. Giant armadillo burrows have been documented as providing temporary homes for over two dozen other vertebrate species. Armadillos primarily use their keen sense of smell to locate their diet of insects, grubs, and other small invertebrates.
Connection to Hansen’s Disease
Armadillos have a natural susceptibility to the bacterium Mycobacterium leprae, which causes Hansen’s disease (leprosy). They are one of the few non-human animals that can contract the disease systemically. The biological reason for this vulnerability is their relatively low internal body temperature, which ranges between 91 and 97 degrees Fahrenheit (33–36°C).
This cooler temperature is optimal for the slow-growing M. leprae bacterium to thrive and spread throughout the animal’s tissues. Transmission to humans is rare but possible, usually occurring through handling infected armadillos or consuming their meat. The nine-banded armadillo is considered a natural reservoir for the disease in parts of the southern United States and South America.