The opossum uses its prehensile tail to bring nesting material such as leaves, grass, and other material into the den. Opossums begin breeding in late winter and early spring. Two to three litters a year are born after a gestation period of only 12 to 13 days. The young are largely undeveloped at birth except for their mouth and front legs. They crawl along a pathway licked by the mother from the genital opening to the pouch and then attach themselves to one of the teats, which usually average 13 in number.
Litters often number more than the available teats.
Those young failing to find a teat will perish. The young opossums remain attached to the teat for about 2 months. Not long after this, they begin to move around within the pouch and may leave the pouch briefly to climb about on the mother's back when they are around 3 months old. Eventually as they ride about on the mother's back they begin to fall off and are then left to fend for themselves. The opossum is often referred to as 'possum by many people, particularly those living in the southern states where the opossum is particular common.