What are Oppossums?

ORIGINAL: Bittelmethis

Posted by Jason Bittel

26 Jun 2012

OPOSSUMS: SURVIVAL MACHINES

The opossum is a waddling, mostly nocturnal creature that looks like a cross between a bleached raccoon and a cartoon rat. If you live in North America, you’ve likely seen scores of them as road kill, a sad fact that does nothing to discourage the opossum’s reputation as one of the dumbest animals on earth.

Despite their ubiquity, most of us don’t know a whole lot about them. For instance, did you know the opossum is the only marsupial north of Mexico? Or that they are smart enough to be litter-trained? Or that they very rarely contract rabies, due to a low body temperature?

If you answered no to any of the above, let’s make a deal. I’m going to geek out about opossums for the next ten minutes. Let’s call it an Opossum Opus. And if you’re good, I’ll reward you with a video of Marci the Opossum chowing down on some chicken.

THE OPOSSUM DIET

They’re not fast or pretty, but opossums are, as a species, rather badass survivalists. And a lot of that has to do with being opportunistic omnivores. In other words, opossums subscribe to the Les Stroud school of thought – Eat Anything That Does Not Kill You. This includes:

A variety of insects, earthworms, slugs, snails, crayfish, lizards, frogs, small rodents (primarily mice and rats), young rabbits, small birds, eggs, grasses, vegetables, fruits, berries, grains, human garbage, and carrion (dead animal material).

What’s more, opossums have powerful, well-developed jaw muscles for chomping through tough stuff like snail shells and, oh I don’t know, bones. They eat a lot of freaking bones. (Wildlife rehabilitators have found opossums fed a diet with an insufficient calcium-to-phosphorus ratio develop crippling Metabolic Bone Disease. Therefore, if you’re trying to rear an orphaned opossum, stop feeding it hotdogs and turn it over to the authorities.)

Opossums also eat snakes. Poisonous snakes. Which brings us to:

OPOSSUM DEFENSES

What the opossum lacks in swagger and grace, it more than makes up in grit. Truth be told, the opossum is a brick grit-house.

Exhibit A: Opossums are pretty much immune to snake venom.

And not just the neighborhood riffraff, like the eastern diamondback rattlesnake with which they have co-evolved. We’re talking timber rattlers, cottonmouths, Russell’s vipers and common Asiatic cobras. We know this because scientists rounded up a bunch of nasties and forced them to bite a bunch of unfortunate opossums, the latter of which responded like it was a mild bee sting.

Using high-pressure liquid chromatography, scientists then sought to identify what makes opossums so damned special. They found it to be a small protein, which they named Lethal Toxin-Neutralizing Factor (LTNF). Like the name suggests, these proteinase inhibitors grab onto and neutralize venoms. Rather like antibodies going after antigens, only LTNF is a naturally occurring opossum protein – not an antibody.

“This is pretty rad,” said the scientists, “but it could be radder. Better kill some rats.” (Scientists are always trying to kill rats; no one knows why.)

So they took some rats and injected them with LTNF, then pumped them full of otherwise lethal doses of venom from Thailand cobras, Australian taipans, Brazilian rattlesnakes, scorpions and honeybees. But the rats just laughed in their faces.

“Dude,” said one scientist, “we have to kill these rats. Do you watch AMC’s Breaking Bad?” The other scientists nodded of course because everybody watches Breaking Bad. So next they tried to kill the rats with ricin, an extremely lethal poison made from castor beans. (How lethal? Just ask Georgi Markov, the real-life Bulgarian defector killed by a ricin umbrella gun. That’s right, I said ricin umbrella gun.)

Alas, the ricin was a no-go. The now-snooty rats danced Ring Around the Rosie. 

“That’s it!” screeched the lead scientist. “It’s time to release the botulinum toxin. Surely this will conquer the awkward opossum’s super serum!” But after many maniacal laughs and a few bolts of lightning, the rats were still alive.

(The paper does not mention what became of the super rats. I can only assume they went on to write “The Secret of Nimh” while the evil scientists lost their rat-killing grant.)

Exhibit B: Despite the rumors, opossums rarely get rabies.

Opossums often get a bad rap for being disease-ridden. But this is probably more to do with their short life span and propensity to eat garbage than anything else. For opossums are actually rather disease-resistant.

According to Dr. William J. Krause (University of Missouri, Dept. of Pathology & Anatomical Sciences), opossums “appear to be resistant to many viral diseases such as distemper, parvovirus and feline hepatitis.” Scientists think a slightly lower body temperature than other similar mammals might play a role. It may also have something to do with the reason we very rarely find rabid opossums, as the virus prefers a toastier climate for its frothy escapades.

Exhibit C: Opossums don’t just “play” dead.

The one thing everyone knows about opossums is the way they “play dead.” But this defense mechanism is far more biologically complex than that time you “played a tree” in your high school’s rendition of The Wizard of Oz. (Not your best work, by the way.)

Playing dead or “apparent death” is a last resort defense maneuver. When confronted, opossums will first bear their teeth, hiss and puff up – anything to make a predator think they’re bigger or meaner than they really are. (Though it should be noted, opossums have kicking canines capable of considerable damage.) They will also high-tail it up a tree when given the option.

In the event that none of this works, opossums come equipped with self-destruct codes. Arms clutched, tongue lolling, they roll onto their side and go catatonic. They may also defecate and release a green, foul-smelling liquid from two paracloacal glands near the base of their tail. And they remain like this – despite being poked, shaken or bitten – anywhere from a few minutes to six hours. Interestingly, young opossums seem to use the trick more than old ones.

Unfortunately, we don’t know much about what’s going on in the opossum’s brain during feigned death. Studies using electrocardiograms (ECGs) and electroencephalograms (EEGs) have found their brainwaves to look much the same whether awake or passed out. (I’d make a Lindsay Lohan joke here, but I don’t want to misconstrue these findings to mean opossums are overpaid idiots.)

Exhibit D: Opossums take a lickin’.

Most predators are highly adapted to track and kill live prey. Once something looks dead and smells like whatever comes out of a paracloacal gland, they seem to lose their appetites and mosey on. But not always.

Sometimes a predator will still take a few nibbles of a catatonic opossum, just to see if maybe it’s something capable of being choked down – like me with vegan food. To combat all this trauma to a defenseless body, opossums seem to have developed a heightened ability to heal.

In a study published in the Journal of Wildlife Diseases, researchers inspected road- killed possums for signs of bones that had been previously broken but since healed. (I.e., not broken by the car that killed them.) Their painstaking work revealed possums to have “a considerably greater frequency of healed fractures” than nonhuman primates, viverids and water voles – other animals to undergo similar research. What’s more, an amazing 31% of the opossums showed signs of having four or more such healed injuries. 

However, living to fake-die another day has its costs. With a femur like that, you know the guy on the right wasn’t winning any races.

THE AWESOME OPOSSUM: PART 2

There’s more where that came from. Click on over to Part 2 of the Awesome Opossum Opus, where we’ll talk marsupial sex, teamwork among opossum sperm, and the cutest little marsupial babies you’ve ever seen. 

But for now, you’ve earned this. Go, Marci, go. 

(Skip to 2:04 for the good stuff. Nevermind the lurking old man nipple.)

A big hats off to William J. and Winifred A. Krause and their e-book, “The Opossum: Its Amazing Story” – published by the Department of Pathology and Anatomical Sciences, School of Medicine, University of Missouri. Much of the bangarang for this post comes from this excellent read.

Image credits: Luke Skywalker Opossum, Fierce Baby Opossum, Asiatic Cobra, Broken Femur