A possum (plural form: possums) is any of about 70 small-to medium-sized arboreal marsupial species native to Australia, New Guinea, and Sulawesi (and introduced to New Zealand and China).he common brushtail possum was introduced to New Zealand by European settlers in an attempt to establish a fur industry. There are no native predators of the possum in New Zealand, so its numbers in New Zealand have risen to the point where it is considered a serious pest.