Armadillos, known for their distinctive armored shells, often spark curiosity about their biology, particularly regarding their reproductive method. A common misconception is whether they lay eggs.
Armadillos Are Mammals
Armadillos do not lay eggs; they are viviparous mammals, giving birth to live young like humans, dogs, and cats. Armadillos belong to the order Cingulata, placing them firmly within the mammalian class. This classification means they share fundamental mammalian characteristics, including mammary glands to nurse their young and bodies covered, at least in part, by hair.
The armored shell, a defining feature of armadillos, is composed of bony plates covered by keratinized epidermal scales. While this unique external structure might lead some to believe they are egg-layers, like reptiles, their internal biology confirms their mammalian identity. All 21 known armadillo species, native to the Americas, give birth to live offspring.
The Phenomenon of Identical Litters
A unique aspect of armadillo reproduction is polyembryony, where a single fertilized egg divides multiple times to produce genetically identical offspring. This phenomenon is particularly characteristic of the nine-banded armadillo (Dasypus novemcinctus), which almost always gives birth to identical quadruplets. These quadruplets are all of the same sex, having originated from that single zygote.
While polyembryony can occur randomly in other mammals, such as identical human twins, it is a regular and expected reproductive strategy in the genus Dasypus. The single fertilized egg implants in the uterus, then splits into four separate embryos. These embryos develop together, often sharing a common placenta. This mechanism, while not fully understood, may offer an evolutionary advantage by ensuring multiple offspring from a single reproductive event.
From Birth to Independence
Armadillo reproduction involves a unique timing mechanism known as delayed implantation. After mating, which for the nine-banded armadillo often occurs in the summer, the fertilized egg does not immediately implant in the uterine wall. This blastocyst remains free-floating in the uterus for several months, typically three to four months, before implantation occurs, usually around November. This delay allows the female armadillo to time the birth of her young for a more favorable season, often in early spring, when environmental conditions are more suitable for raising offspring.
Once implanted, the gestation period lasts about four months. Armadillo pups are born in a relatively developed state. At birth, their shells are soft and leathery, not yet hardened, resembling the texture of human fingernails. These shells gradually harden over a few weeks to months.
The pups are dependent on their mother for nursing, typically for two to four months, during which they remain in the burrow. They begin to forage alongside their mother and generally become self-sufficient by three to four months of age, reaching sexual maturity around nine to twelve months.