Virginia opossums are the most unusual mammal in North America

What makes a species successful? Is it its intelligence? Is it its new and unique adaptations that make it able to adjust to a changing environment? How about none of the above?

The Virginia opossum is a bit of anomaly. Its closest relatives are other New World opossums, which are all marsupials, which are quite numerous in the tropical reaches of this continent. There are about 100 species of opossum in South America.

But in these northern reaches of the Americas, only a single marsupial can be found.  In Australia, marsupial mammals have a very hard time competing with placentals, but in North America, the Virginia opossum is thriving. Indeed, its range has expanded continuously since European settlement.

It is believed that the original range of the Virginia opossum in the United States was confined to the subtropical south. It could be found from Virginia to East Texas. By the end of the Civil War, its range extended to the southern edge of the National Road (today’s US 40).  Today, its range extends into southern Minnesota and Wisconsin, parts of Maine, and southern Ontario. For some reason, this species was introduced to California, and now its range extends along the Pacific Coast to British Columbia. The animal can now be from from British Columbia and Ontario to Costa Rica.

Now, the success of this species is not because it has any novel adaptations. It is basically a generic mammal that eats virtually anything. Its has many unspecialized teeth. In fact, it has more teeth than any other mammal in North America. Its shaggy coat has no undercoat, and it cannot dig its own burrows. It has a prehensile tail, but it is unable to hang by its tail, as is portrayed in far too many cartoons. The truth is that this animal has been very successful without specialization. It hasn’t changed much since the early Paleocene or the late Cretaceous.

It is also not a particularly intelligent animal.  Proportionally, thas the smallest brain of any species of mammal in the continent. (There is, however, a terrible urban legend based upon a methodologically poor study that said that opossums were smarter than dogs or pigs. This simply isn’t in keeping with what we already know. Marsupials generally have lowerintelligence and smaller brains than their placental counterparts. The 45 pound dingo had a significantly larger brain than the 70 pound thylacine.)

As Jesus said in the Beatitudes: “Blessed are the meek, for they shall inherit the earth.” (Matthew 5:5). Now, I don’t know how that applies to the nebulous discipline of theology, but I do know that it fits in with what European man has done to the natural history of this continent.

We have slaughtered all the big animals on this continent. Once there were great herds of wapiti (elk) where I’m sitting right now, along with teaming bands of bison, which were harried by packs of wolves.  The cougar is also gone, although a few people claim to have seen them slinking through the undergrowth. All of these have disappeared.

But with the extirpation of the great beasts, the ecosystem was opened up for new expansion by the smaller creatures. The raccoon has spread north and west into parts of Canada where it was never known before. The coyote now lives through most of North America from Alaska to Panama.

Animals that can eat just about anything and that aren’t that big enough to cause people to kill them out fear really do well in this environment. Virginia opossums eat just about anything; they will regularly raid trash cans and left out stores of cat food, which are about the most common food sources in the suburbs.

Further, they can reproduce in very large numbers. Although they live only one of two years, a female opossum can give birth to two to four litters in her lifetime that contain as many as a thirteen offspring per litter. The opossum female gives birth to dozens of offspring, but only the first 13 to attach themselves to the nipples in her pouch survive. The female opossum has 13 nipples, arranged in a circle in her pouch.

They also have another behavior that prevents predation. Contrary to what urban legends say, the Virginia opossum doesn’t play dead. Instead, when it is really scared, it goes into an involuntary coma-like state and releases some stinky green fluid from its anus. Most animals will leave it alone, because who wants to eat something that is dead and squirting stinky juice out of its butt? (Of course, I had a dog, the “golden boxer,” that once caught a large, almost white opossum. She carried it home in her jaws, and as I was watching her carry it, the opossum came to its senses in her jaws. It look around, and suddenly became scared enough again to go back into its “coma.” Apparently, it was out of its stinking anus juice, but that wouldn’t have bothered this particular dog, which reveled in killing skunks. She dropped the opossum near the back door, and both of us went inside. Within an hour, this opossum had come to its senses and wandered off.)

Now, those adaptations really do help the opossum survive, but it is still a tropical species. It is not really adapted fully to the northern parts of its range. During the worst part of the winter, it will use the burrows of other mammals to keep warm, and it sometimes uses attics. But it is really quite common for these animals to get frost-bitten and lose the tips of their ears, tail, and toes during the winter.

Climate change and the tendency of this species to grow a somewhat longer coat have allowed it to expand its range. I don’t think we’ll have Artic opossums any time soon, but their range in Canada and the Upper Midwest is likely to continue to expand.

Now, it is often said that people eat these things. I have yet to meet anyone who has eaten them, and I am from West Virginia. I read in a  wild game book from Missouri, which was written in the 1970′s, that people who want to eat them should capture them alive and feed them table scraps for a couple of weeks before slaughter. This changes the flavor of the meat, which is thought to be degraded from the opossum’s less than savory diet.

I’ve also seen these animals come in colors that vary from almost white to quite black. Supposedly the lighter colors are more common at the northern edge of the range, but in the middle of the rage, which is where I live, these animals are usually gray animals with a few that are almost white and a few that are almost black.

So because our civilization has removed most of the larger, “sexier” species from the ecosystem and then paved over so much of the land, animals as banal as the oppossum now thrive.