The Virginia Opossum
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The Virginia opossum, or 'possum, as he's usually called, is a docile and timid animal who's received a bum rap. Maybe this is because many people think he's a huge rat. In fact, this "rat" is no rat. He's the only marsupial living in the U.S. and is related to kangaroos, koala bears, wombats, wallabies, Tasmanian Devils and other "pouch" mammals.
Marsupials are unique in that they undergo part of their development in their mother's womb and the rest of it in her pouch, a sort of external womb. Appropriately, the name of the opossum's order, Didelphis, means "double womb." "Opossum," comes from apasum, an Algonquin Indian word for "white animal."
Worldwide there are about 65 species of opossum (oh-POSS-um) and the one living in the U.S. is the Virginia opossum (Didelphis virginiana). These opossums were first seen by European colonists in, yes, Virginia.
Opossum-like ancestors first appeared about the time dinosaurs went extinct, about 65 million years ago during the Cretaceous Period. Opossums have survived so long because they're very adaptable: Change their habitat, they'll make do with the new one. Remove their usual food sources, they'll find new ones.
Virginia Opossum skeleton
(photo: Allen Gathman / Flickr)
Virginia Opossums are about the size of a large house cat, adults weighing 8 to 14 pounds, with males being larger than females. They have a long, pointy face with black eyes and a pink nose. Their whiskers are long. The ears are hairless, black, and tipped or edged with white. White hair covers their face and the body is a sparse, coarse mix of grayish and blackish hair. The tail is hairless, scaly-looking and long. It's also prehensile, meaning it can be used to hold or grasp things. Monkeys are another animal with a prehensile tail; they use it for hanging. Opossums can hang by their tail -- you may have heard this is how they sleep -- but that's not so. They're are too heavy to hang for very long. Opossums have very keen senses, except for their eyesight, which is rather poor.
Virginia opossums have 50 teeth, the most of any U.S. land mammal. When they open their mouth, all those teeth are exposed and look menacing. It's deceptive, because opossums are mild mannered and will move away from confrontation, given the opportunity.
Note the flexible toes.
Opossums have five dexterous toes (some experts call them fingers) on each foot. The hind feet each have an opposable thumb (technically, a "hallux"). In the photo to the right, notice how flexible the toes are as they grasp the railing. The back feet are even more dexterous. All their toes are clawed except for the thumbs, which are used to grasp branches when climbing.
Opossums emit sounds. They hiss and snarl very convincingly when threatened and mothers purr to their young.
They have no body odor because they lick themselves constantly. This, at least in part, has to do with thermoregulation of their body temperature -- they lack sweat glands and the evaporating saliva helps to cool them.
Opossums try to act very scary by
flashing their teeth and hissing. Even
young ones, like this.
(Lisa Wright / EOL)
Virginia opossums are nocturnal and solitary. Many folks have seen one only as roadkill or in the spotlight of a suddenly-switched-on porch light. Coming face-to-face, opossums may freeze in place, but often they just turn and move away. For them, moving usually means shuffling in a clumsy-looking waddle. If circumstances compel them, however, they can run at about 4 miles per hour -- equivalent to a fast walk for a human. Opossums know this isn't fast enough to save them from most predators, so typically they head for safety. They might crawl into a den, scale a tree (they're expert at this), or drop "dead." Opossums are able swimmers, too.
Opossums are well known for feigning death, or "playing 'possum." They certainly look dead when they "play" at it, but they aren't actually acting out a theatrical role. It's apparently an involuntary, stress-induced nervous collapse, and it's convincing.
This opossum isn't dead; he's
They fall over on their side, curl their body, open their mouth in a grimace, let their tongue hang out, and stare with unmoving eyes. This convinces some predators who don't eat dead meat to move on. Sometimes opossums will become even more undesirable by defecating, vomiting or drooling. When it's safe, they get up and go about their activities with no ill-effects.
Opossums don't always play dead. Instead, they may try to bluff their way out of trouble with a flash of teeth and scary snarling. (Baby opossums open their mouths wide, in imitation of their mother, but their toothless gums just aren't that threatening!) Opossums always try to avoid confrontation and are sometimes called the pacifists of the animal kingdom. Like all wild animals, however, they can be aggressive if they have no other option.
Opossums have a reputation for being very dumb because of their slow movements and small brain size (five times smaller than a raccoon). Yet, owners of rescued young opossums, who could not be released back into the wild, say they can be litter box and leash trained, love to be held and to snuggle, and will greet you at the door when you return home. They also claim that opossums will come when their name is called.
Virginia opossums are harmless, beneficial visitors to backyard wildlife habitats. They're quiet, they don't dig or claw. They don't eat flowers or chew up the vegetable garden. Instead, they arrive, eat a rodent and some snails, scoop up some insects, munch on a piece of fallen fruit and clean up our garbage, if we've left it accessible. All in all, opossums are pleasant, helpful critters to have around.
Although well adapted to city life, the natural habitat of opossums is forests, brush, wastelands, and wet areas, such as marshes and streams. Opossums were originally a species of the southeast U.S., but now inhabit much of the southern half of the U.S., plus California. Opossums have been puzzling scientists in recent years by moving northward, even though their sparse hair makes them susceptible to frostbite in colder climates.
You name it, they'll eat it. This is probably one factor contributing to opossums' survival since prehistoric times. In addition to "people food" in the garbage can and pet foods left outdoors, opossums eat rodents, frogs, insects, fruits, grains and carrion.
The wildlife rehabilitator who treated this injured baby says possum babies are her favorites because "they're so sweet."
Cover and nesting
Virginia opossums are solitary animals who generally nest alone. Females, however, will sometimes use daytime nests together. Opossums' feet are soft and delicate with small claws, not designed for digging. So, they look for existing nest sites that will keep them warm and safe, such as old burrows, drainage pipes, hollow logs, old squirrel nests, rock crevices, woodpiles or under a porch. Even in a chimney. They line nests with soft materials, like grasses and dried leaves.
It's interesting how an opossum goes about transporting nest-building materials: First he uses his mouth to gather up materials. Then he takes them from his mouth with his front feet. The front feet transfer the materials to the back feet and from there they go to the tail.
A female reaches sexual maturity at about seven months of age and can breed around every 28 days year-round. However, peak time is late winter to early spring, and she is in estrus only about 36 hours at a time, so the window of opportunity is very narrow for the males. Males go their own way after mating and don't participate in raising the young.
She typically has two or three litters a year, each with 8 to 12 young. Like kangaroos, opossums have a very short gestation period -- just 13 days. After their birth, the young continue their development in their mother's pouch (technically called a marsupium). But first they must get from the birth canal all the way up to the pouch. Watching the babies, who weigh 1/200th of an ounce -- the size of a bee -- crawl from the mother's birth canal to the pouch is an edge-of-your-seat thriller. Not much more than embryos, the babies are hairless and almost transparent.
Their mother has prepared the way by licking a path through her hair for them to follow. With a swimming motion, they must pull themselves blindly (literally, since their eyes are closed) along this path. It's only a three- or four-inch trek, but for these little guys, that's a very long trek. And, it's treacherous. A sudden move by their mother and they'll all fall off and perish. The weaker babies will not make it, regardless.
Those who do enter her fur-lined marsupium will find one of 13 teats aligned there in a horseshoe arrangement. This is their lifeline to further physical development and they hang on tightly. If more than 13 babies (called joeys) enter the marsupium, then the extra ones will die.
Two months later and the size of a mouse, they've begun to outgrow their warm, protected environment that's now stretched almost to its limit. Ever so cautiously, they peek out. Then they duck back inside. They peek out. They duck back inside. They'll do this many times over the next couple of weeks until finally they climb out -- still clinging to the teat! They'll stretch just as far as they possibly can, but won't turn loose.
Eventually, in a tense moment of bravery, they open their mouths and let go. Then comes the second important climb of their lives: up to their mother's back (not her tail, contrary to myth), where they tightly grasp her hair with their feet and tail. If one falls off, he'll makes "hussing" sounds, and his mother will make clicking sounds in response. If she's unaware he is gone, however, she'll continue on without him, and at this young age he'll perish.
A mother loaded with babies.
Those on her back are about to go for the ride of their life. They travel widely in search of food, staying in one den only three or four days before moving to the next (except in winter when a nice, warm, well-built nest invites a longer stay.) Their mother will use her whiskers like a cat, to feel her way along dark passages, and her excellent sense of smell will locate food. They go up and down trees, through thick bushes and brushpiles, into garbage cans and compost piles, under the porch, under fences, through drain pipes and culverts, and into hollow logs. They might even go into the water if their mother swims across a creek. (They can stay dry by squeezing back into her pouch, as she can amazingly seal it so tightly it becomes waterproof.)
The joeys learn how to forage for snails, slugs, beetles, and other insects, and to feast on carrion, garbage, birdseed and fallen fruit. They learn how to kill and eat a rat, and a snake, too. They learn the best ways to hide and defend themselves, and where to live.
After a few weeks of tutoring they begin life on their own four feet by simply loosening their grip and dropping off their mother. By now, they're about seven to nine inches long, excluding their tail. They share their mother's den for a short time, then leave to establish their own territories.
Opossums can live up to 10 years under ideal conditions, but most don't make it past their first year because of heavy predation by dogs, foxes, coyotes and owls. Autos take a huge toll -- it's thought the opossum's fondness for carrion draws them to roadkill, where often they also become roadkill. At one time, opossums were widely hunted for their fur and meat.