To most people, Opossums, Didelphis virginiana, appear to be oversized rats often seen dead on the side of the road. Although their naked tails and body shape appear similar to rodents, the two are not closely related. Opossums are marsupials, or mammals with pouches, (As are kangaroos, koalas and wallabies) whereas rodents are placental mammals. (As are humans, dogs, cows, etc.) There is fossil evidence of Opossums dating back to the dinosaur extinction. The Opossums we know in North America today were thought to have crossed over from South America via the Isthmus of Panama about 3 million years ago. Their northern range may be limited by their naked tails and ears, which can become frostbitten if it is too cold.
One of the things the Opossum is famous for is “playing possum”, or pretending to be dead in the face of danger. Opossums can keel over and remain immobile for hours in response to stress, although they are most likely unaware of the act they are putting on, instead going into a form of shock. This defense mechanism may discourage some predators, but also leaves the Opossum vulnerable. Modern day “predators” such as automobiles tend to kill things that don’t get out of the way.
Opossums are nocturnal and appear to walk around clumsily searching for food. They will eat almost anything they get the opportunity to; carrion, pet food, seeds, insects, and berries are all on the menu. They are climbers and even have opposable “thumbs” on their feet. They are usually found alone, and often wander throughout a larger home range. Breeding season can begin as early as late January, and again in early summer for a second litter. Because they are marsupials, Opossums are born developmentally early, after only 13 days gestation. When they are born, they climb up the mother’s abdominal fur and into her pouch, where they attach themselves to a nipple. They will remain attached for 2 months, after which they will emerge from the pouch and cling to their mother or follow her around until they become independent about a month later. They are not long lived, many not making it to their second year.
While most people encounter Opossums as road kill, the fact that they have been around for millions of years should attest to their resilience. Their uniqueness as North America’s only Marsupials should also be considered. The next time you see, perhaps you can appreciate that they are much more that over-sized rats!
