Good Natured: The Virginia Opossum
As we head into a brand-new year, let's take a look at an old friend: the Virginia opossum, Didelphis virginiana.
Now this critter is so familiar, most of us drop the “Virginia" part from the name; some even go so far as to drop the “o" and go with simply possum. Either way, these animals have quite a story to tell.
Their ancestors hail from South America, where they expanded their range northward, first to Central America after the Isthmus of Panama formed (about 3 million years ago) and then into North America (about 600,000 years ago). Today they can be found from Costa Rica to southern Ontario, Canada, and their range is still growing.
Besides their successful generalist ways, these critters are also renowned for their ability to “play possum"—that is, appear very dead. This reaction to extreme fright looks like something they can control, but it's actually an involuntary response that produces a coma-like state, complete with lowered heart rate and respiration, and the release of various bodily fluids.
As gross as it sounds, it can be an effective defense against certain types of predators. Some animals really do need the thrill of the chase in order to stimulate appetite, and when stinky, still-as-death prey doesn't fill the bill, they're apt to move on to more appealing forms of food.
Opossums have another, lesser-known defense: Drool. They chew and jaw until saliva drips out of their mouth and even bubbles out the nose. All that goo makes them look sick and unappealing and can cause a predator to bypass the whole dribbly mess.
Then we have another entire set of physical adaptations that make opossums so unique among North American mammals. Opossums are our only native marsupials! They carry their teensy-as-a-bean newborns around in a pouch where the young'uns nurse and grow; once large enough, they then climb out and ride around on mom's back.
The gripping skills they develop at this early age serve them well later too: Opossums are expert climbers. Aided by a cool opposable toe on each hind foot as well as a weakly prehensile tail, they can amble up a tree, fencepost or deck railing with no trouble at all. (Speaking of prehensile…opossums can grip light things, like dried leaves, with that tail, and they can use it for balance when climbing, but no matter what you may have heard, they don't sleep hanging by it.)
Opossums have 50 teeth, more than any other mammal on the continent, and aren't afraid to show them. They may bite when cornered, but their teeth primarily are used to consume an extremely varied diet of carrion and rodents, insects, plant matter and of course all the leftovers humans leave behind, including French fries in parking lots, snacks on playgrounds, and cat food and dog food on porches.
These animals also have one of the smallest brain-to-body mass ratios, but their extreme adaptability lets them flourish pretty much wherever they set foot. As we noted, they're not fussy eaters; they're as comfortable under a deck or shed as they are in a secluded woodland nook; and they can adjust the sex ratios of their offspring in response to various environmental conditions to maximize survival. How cool is that?
You might have heard that opossums are tick vacuums, slurping up as many as 5,000 a season. I gotta say, I was skeptical of that laboratory-induced figure when it came out, and was happy to see the scientific community challenge it too. Last year researchers at Eureka College in central Illinois tackled this topic, examining 23 manuscripts on opossum diets as well as the stomach contents of 32 actual opossums. And you know how much evidence they found of ticks being consumed? Zero. Zip, zilch, nada.
Which is just fine, considering all the other things they eat as part of nature's cleanup crew.
You might think, given their expansive range and indiscriminate palate, and those cool opposable toes, that opossums are poised to take over the world. Who knows, someday they might. But their northern advancement might be slowed, at least for the time being, by one major disadvantage: They are not well adapted to cold weather.
Just look at them… Bare ears. Bare tail. Thin fur.
Next time you see an opossum, take a moment to assess its overall appearance. Are the ears small and ragged? Chances are they've been frostbitten. What about the tail? It is also vulnerable to cold, and will look stumpy over time.
Fewer than 10% of opossums survive their first year, and an opossum of two or three years of age is an elder indeed. Their family though, the Didelphidae, has survived for 65 million years on this planet. With that sort of success, they could be around 65 million more. Happy 2023, li'l D. virginiana!
Pam Otto is the outreach ambassador for the St. Charles Park District. She can be reached at firstname.lastname@example.org.