Only The Strong Survive: The Virginia Opossum

Lucy the leucistic Virginia opossum resting peacefully. Image taken at the San Francisco Zoo.

Where do I even begin with opossums? They are one of my favorite mammals and I believe they are a little misunderstood sometimes. They’re very important animals, that eat carrion (dead stuff), garden pests such as snails and slugs, snakes and even over-ripe fruit (preventing it from rotting), so they play an important role in our ecosystem. Furthermore, if we took opossums out of the ecosystem, the niche they fill is easily taken over by skunks, raccoons and rats. However, opossums are probably preferable (although I do love skunks, raccoons and rats), because they don’t dig up your yard and even cooler, they have an immunity to rabies and distemper!

Speaking of immunity, these adorable creatures are immune to the venom of rattlers, water moccasins and copperheads. They do have to worry about parasites and interestingly enough, frost bite and the often resulting gangrene. They used to live only as far north as Virginia and Ohio, but with the arrival of Europeans, these animals were introduced farther north (up to British Columbia) as small game after WWII. However, since they evolved in warmer climates (a long time ago, as they were around with the dinosaurs), they are ill-equipped to deal with harsh winters, being unable to hibernate and having naked hands, ears and tails. Yet these hardy animals survive there and in fact do quite well, frost bite aside.

One thing I find particularly endearing about opossums is their hands and how they use them. They actually have opposable “thumbs” on their back feet, so they are excellent climbers (and swimmers) and sometimes use their hands to eat.

Lucy the opossum showing us her hand. Image taken at the San Francisco Zoo.

They also use their hands to groom their faces, kind of like kitties. This is Henrietta, my all time favorite opossum grooming herself:

I can see why some people would be intimidated by opossums. They do have more teeth than any other mammal in North America (50, to be exact) and if they are scared, these relatively peaceful animals will expose their teeth and hiss, as a first line of defense. To see what their teeth and skull looks like, here is a site with a 3D opossum skull that you can rotate around. It’s pretty cool. While I have been hissed at, most often I see opossums using their teeth like this:

That is Henrietta again, very gently taking and nomming grapes from my hand, with the most adorable smacking sound.

Now I mentioned that they will hiss and show their teeth as a first line of defense, but if that should fail, their body has an automatic reaction that is also pretty neat. Have you heard of the expression “playing ‘possum?” These cuties will actually slip into a comatose state, with their mouths open, drooling and everything, to appear dead. They will even emit a foul smell from their anal gland and their heart and breathing rates drop. It’s quite convincing and many predators, such as foxes and bobcats, will leave them be.

After all of this, I think the most interesting thing about Virginia opossums is their mating and reproduction. They are the only marsupial found in the United States. The male opossum courts a female by clicking its teeth and following her around. At some point the female accepts his appeals and he mounts her in a typical mammalian fashion. Then they will fall to their right side. Yes, almost always to their right side. If they stay upright, or if they fall to their left side, then the female is not likely to be inseminated. The opossum penis is forked, which is probably why people used to believe that male opossums would inseminate the females through their noses and that the females would then sneeze their babies into their pouches. Yes. People really believed that. Their sperm are also paired and can only swim properly in pairs. If you separate a pair of sperm, then each sperm just swims in circles. I could not make this shit up.

Alright, the male is now done and everything else is up to the female. Like most marsupials, she has a pouch and the incredibly tiny young are born shortly after fertilization and climb into her pouch. However, for opossums its not quite so easy. Up to 25 small opossums are born. They are all so tiny that you could fit all of them together in a teaspoon.  And they will all race to mom’s pouch, because in an extreme case of survival of the fittest (not the Darwinian definition of fitness, but in terms of physical strength and endurance) only 13 will be able to attach to a nipple. (In “North American Wildlife” by David Jones, he calls it the “world’s cruelest game of musical chairs.”) That’s right mom only has 13 nipples and once a young opossum attaches to a nipple, it swells up and they are essentially locked on until they are developed enough to leave the pouch (about 2 months). The rest of the babies, if they even make it into the pouch, just die. While we’re on the topic, the Virginia opossum is one of the few mammals that has an odd number of nipples. She has 12 nipples in a circle, and then one right in the middle. They are truly unusual mammals.

One last thing that I think is interesting. While opossums do have prehensile tails, adults cannot hang by their tails, contrary to popular belief. They use their tails to aid in climbing and they will collect nesting material with them as well. On the other hand, young opossums can hang by their tails.

Baby opossums hanging from their tails. Image taken by Frank Lukasseck/Corbis.

While this picture is not mine, I simply had to include it because it is unbearably adorable. And just for shits and giggles, I’ll add just one more photo of my princess, Henrietta. I want to point out that Henrietta was rescued from her dead mother’s pouch and was a wonderful part of the San Francisco Zoo’s education programs. She could have just died and so I’d like to point out that if you see a dead opossum, it might be in its comatose state or it might still have living young in its pouch, so it’s important to contact the professionals to check it out.

Henrietta the opossum. Image taken at the San Francisco Zoo.

So there you have it. The Virginia opossum. I would like to note that throughout this post, I am always writing about the Virginia opossum and not any other opossum species. As you can see, these animals are non-threatening, clean, adaptable and beneficial survivors. I hope you all can appreciate them as much as I do. To learn more about them, here is a fantastic site by the Washington Department of Fish and Wildlife and here is a cool site to help you find opossum tracks.