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The Difference Between Rats & Opossums

The obvious difference between the lone species of opossum in North America -- the Virginia opossum (Didelphis virginiana) -- and the various rats inhabiting the continent is that the female opossum possesses a pouch. Being a marsupial, the opossum has teats in its pouch where its young suckle until old enough to climb out and make the transition to a solid diet. Rats lack such features; that and other differences distinguish them from the opossum.

Size and Features
- Opossums have a hallux -- a thumblike toe used for grasping.
  
  The opossum is the size of an average house cat, with weights between 4 and 14 lbs. The prehensile tail is naked and makes up much of its length, like that of a rat's, but it can grasp onto tree limbs, allowing the opossum to hang from a branch for a short time. Rats are much smaller than opossums, with even the largest species, such as the Norway rat (Rattus norvegicus,) weighing just over a pound. Opossums have what the New Hampshire Public Television Network Nature Works describes as a thumb on its hind legs, used for grasping branches when the animal climbs. Rats have no such feature.
Geography
- Some rats are extremely adaptable, so much so that nonnative types like the Norway rat and black rat (Rattus rattus) occur across much of the continent. Other rats have smaller ranges, including some that dwell only in desert areas in North America. The range of the Virginia opossum extends from the eastern Great Plains across much of the eastern United States, going south into Mexico. Populations of the opossum also occur along the West Coast.
Habitat
- An opossum makes its home in a number of different ecosystems, including marshes, swamps, open forested areas, farmlands and near waterways. A rat's habitat depends upon the species. The group known as cotton rats lives in grassy regions, and have an affinity for thick vegetation. The rice rats prefer a wet environment, living in marshy places. The wood rats adapt to rocky locations, woodlands, swamps and fields. Nonnative species like the Norway rat often live in urban areas in close proximity to humans.
More Distinctions
- The rat diet focuses mostly on plants and grains, but rats also eat carrion, garbage and other foods. The opossum dines on a wide array of items, including carrion, plants, fruit, insects and small mammals. Opossums will have as many as three litters of young per year, while rats vary in this endeavor. Some have just one litter annually, while species such as the Norway rat will have as many as 12 litters in a single calendar year.

Nature