Opossum are North America’s only marsupial, coming from South America over the Panamanian land bridge about 3 million years ago. 69 other species exist in South America. Of particular interest is the fur-lined pouch where the babies spend two months growing from bumble bee to chipmunk size. Nocturnal animals, they mark home ranges, pecking orders and can share nests. Smells have a role in the opossum society. They are unsurpassed omnivores (called "living vacuum cleaners"). They are even immune to rattlesnake venom, thereby adding rattlesnakes to it’s diet when available. Since food is found everywhere, no need for a permanent den. Opossum simply establish a temporary home range, forage throughout the area for several days using the same den, then, when the food has been used up, the opossum moves on to a new area.