Virginia opossum mothers carry up to a dozen babies, and it’s common for one to fall off if she’s startled by a dog, attacked by another animal, or spooked by a car. She will not risk her life—or the lives of the babies still in her pouch—by returning for the one that was dropped, and she may not even realize she lost it. Because of this, reuniting a baby opossum with its mother is extremely rare. If the baby is the size of your hand or under about seven inches, it cannot survive on its own and needs to be brought to a wildlife rehabilitator immediately.