Playing 'Possum

We recently had some kind of critter invade the garden in the night and gnaw off tomato seedlings and other vulnerable young vegetables. We struggled with protecting the delicate plants, as we tried to figure out who was the culprit. We at first suspected rabbits, but after several failed attempts at intercepting and identifying the perpetrator, we bought a live trap. The very next morning I entered the garden to greet a very unhappy opposum staring at me from his cage. I drove him up the road a few miles and released him into the woods.

That incident led me to do some investigation into the Virginia opossum, hoping that I could figure a way of discouraging these critters from invading the garden in the future. We have been growing vegetables for over three decades now and this is the first time opossums have raided us. We've dealt with voles, rabbits, countless insects, and deer, but the opossum was a new threat.

The local opossum (Didelphis virginiana) is North America's sole marsupial—which is a type of mammal that lacks a placenta. Like kangaroos, the opossum gives birth to tiny fetal-like creatures, who scramble into mom's pouch, where they spend their first few months of life. The opossum looks like a rat with a very long, pointed head. It's about the size of a domestic cat, but its brain is only one-third of the size of a cat's brain. (Now, that's really dumb! I've written on this blog a few times about how the cognitive capability of the household cat is quite inferior to a dog.)

The opossum is a nocturnal creature, rambling around in the night for its food. Its nose is extremely sensitive, which compensates for its poor eyesight. It is truly an omnivore, as it will dine on grains, snakes, mice, chipmunks, human garbage, insects (ants, ticks, flies, spiders, etc.), as well as tender vegetables. That last item spurred this blog.

Most Americans are familiar with the term “playing 'possum,” which refers to the animal's habit of suddenly falling down and playing “dead” when it's threatened. It does a remarkable job of looking dead. Its eyes are open, its tongue flops out, its heart rate halves, its breathing rate drops by a third, and it oozes a foul-smelling liquid from glands near its anus that reeks of death. It can lie lifeless for up to six hours.

The opossum is a hairy critter (rat-looking, as I said) with a hairless tail that looks eerily like a snake. It has more teeth than any other similar mammal. What's especially unique is that it has an opposable thumb on all four feet; making them look uncannily like human hands. It's a very bizarre little critter!

Another fascinating fact about the opossum is how it came to North America. Millions of years ago North America was inhabited only by placental mammals, while South America's mammals were predominantly marsupial. About three million years ago the Isthmus of Panama arose as sea levels dropped, connecting the two continents. Some marsupials migrated north; some placental northern mammals headed south, through Panama.

Thereafter, similarly-behaving species (one kind marsupial, the other mammal) came into competition, and when they did, the placentals almost always had the advantage. As a result, many marsupials in South America went extinct, giving way there to their placental competitors. In North America, all marsupials went extinct, except for the intrepid opossum. Maybe its ability to play dead so effectively helped it to persevere?

I find it fascinating that we humans evolved from placental mammals—primates—who resemble the opossum. It makes me wonder what if the marsupials had been more fit than placental mammals, and they had won the evolutionary competition? Would the world's most intelligent critter today be a marsupial with opposable thumbs? It's a reminder that, if we could roll back the clock a few million years and replay evolution, today's mix of species would be very different. The fact that humans came out (so far, anyway) as the dominant species was not preordained.