According to William B. Davis in his book The Mammals of Texas, breeding takes place from September to December, with the older females breeding first and the younger ones later.
The young are born in March and April. The female has four mammary glands – two on the upper chest and two on the lower abdomen – just the right number for the quadruplets that are born each time.
The four young, always of the same sex, come from a single fertilized egg. The embryo starts as a single individual; however, through a process of bisection, followed by a second sub-division, four clonelike embryos are formed. Each is enclosed in its own membrane sac.
The young are born with their eyes open and are able to get around within a few hours. With the exception of their soft, leathery shells, the young are miniature copies of the adults. Since the shell cannot be shed and replaced with a larger one, it must increase in size as the young armadillo grows, and it does not harden until adult size is reached.