Didelphimorphia Temporal range: Upper Cretaceous – Recent
Virginia opossum Didelphis virginiana
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Infraclass:	Marsupialia
Order:	Didelphimorphia
Family:	Didelphidae

Opossums are the largest order of marsupials in the Western Hemisphere, the Didelphimorphia.

They are often called possums, though that term is more properly applied to Australian fauna of the suborder Phalangeriformes.

The Virginia opossum was the first animal to be called an opossum: the word comes from the Algonquian language, and means "white beast." It was one of the few South American marsupials to establish itself permanently in North America after the Great American Interchange, and the only one to survive there today.

Scientists used to believe that opossums are large numbers of ticks, but now they think they do not. Wildlife scientist Cecilia Hennessy thinks this belief came from a paper called "Hosts as ecological traps for the vector of Lyme disease." Hennessy did her own study and found that opossums do not eat many ticks. She and her team looked at opossums' stomachs and found animals without bones like beetles and worms, animals with bones like amphibians and small mammals, plants including grass, leaves and seeds, and garbage.