Opossum

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.
Opossums can help slow the spread of Lyme disease and Rocky Mountain spotted fever because they eat deer ticks and other ticks that carry the germs for these diseases. One opossum can eat 5000 ticks each year. They also eat garden pests, for example slugs, and animals that can carry disease, for example mice and rats.
Marsupials like opossums are born before their jaw bones have grown enough for them to drink their mothers' milk the way other baby mammals do. Scientists from King's College London found that opossums and other marsupials use tissue from their inner ear to make a temporary jaw so they can feed and grow.