Beneficial and docile, a marsupial deserving of respect
There are more than 60 species of opossums in the world. The only one occupying the United States is the Virginia Opossum (Didelphis virginiana), first seen by European colonists in, yes, Virginia.
Opossums (oh-POSS-ums) are marsupials, mammals that undergo the early part of their development in their mother’s womb and the rest of it in her pouch. Other marsupials include kangaroos, koalas, wombats, wallabies, Tasmanian Devils and…possums. That isn’t a misprint. Possums aren’t opossums. Except for being marsupials, possums are a group of entirely different animals who inhabit Australia and surrounding islands.
The earliest marsupial species evolved in North America and moved south to South America. The direct ancestors of the Virginia Opossum evolved later in South America and moved north to the southeastern U.S. During the late 1920s and the 1930s they were introduced into western coastal states and have now expanded northward into southern British Columbia. They also extend south into Mexico and Central America, where most of the other opossum species are found.
Virginia Opossums have existed since the Pliocene Epoch, two to five million years ago.¹ They’ve endured the passage of time astonishingly well, and largely unchanged. How? Scientists don’t know for sure, but think it’s probably because they’re masters of adaptation: Change their habitat, they adjust to a new one. Remove their usual food sources, they change their diet.
Virginia Opossums are in the order Didelphimorphia and the family Didelphidae. Their genus name Didelphis is Ancient Greek for “double womb.” As you read on, you’ll see how appropriate that name is. “Opossum,” comes from apasum, an Algonquin Indian word for “white animal.”
Virginia Opossums are 2 to 3 feet long, plus a tail length of 8 to 13 inches. Sources vary widely about their weight, with some reporting a range of 4.6 to 6.2 pounds and others as high as 8.8 to 13.2 pounds. Males are usually larger than females.
Opossums have a long, pointed face with black eyes, long whiskers and a distinctive pink nose. Their ears are black and tipped or edged with white, and hairless. White hair covers their face, and their body is a sparse, coarse mix of grayish and blackish hair.
Their tail is hairless, scaly-looking and long. It’s prehensile, which means it can be used to hold or grasp things. You may have heard that opossums sleep while hanging by their tail, but that isn’t so — they’re too heavy to hang for very long. The sparsity of hair on their body makes them susceptible to frostbite, preventing them from inhabiting regions that are too cold.
Opossums have 50 teeth, the most of any U.S. land mammal. When they open their mouth, all those teeth are exposed and look very menacing. It’s deceptive, because opossums are mild-mannered, unless deliberately provoked, and will move away from confrontation, if possible.
Their feet are bare on the bottom. They have five hairless, dexterous toes (some experts call them fingers). Each of the hind feet have a thumb (technically, a “hallux”). All their toes are clawed except for the thumbs, which are used to grasp branches when climbing.
They have no body odor because they lick themselves constantly. The licking, 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 have a keen sense of touch and smell, with 1,188 genes devoted to smell. (By comparison, humans have 396 olfactory genes devoted to smell and dogs have 811.²) Opossums have poor eyesight and their senses of hearing and taste are rather weak, also.
Opossums make only a few distinct vocalizations. They hiss, snarl, click and screech, and may make all of these sounds when showing aggression. Clicking is also made by males in mating behavior and by females when around their young. The young also make clicking sounds. Some sources say mothers also make a purring sound to their young. Listen to baby making clicking sounds.
Opossums have a reputation for being dim-witted because they move slowly and have a small brain size (five times smaller than a raccoon’s). However, researchers found in a series of tests that opossums are better than dogs, cats and other animals at remembering the location of food hidden in a maze; only humans were superior to them. And, owners of young rescued and un-releasable opossums say they can be litter box- and leash-trained, love to be held and to snuggle, and will greet them at the door when they return home. They also claim that opossums will come when their name is called.³
Opossums are solitary, except when mating or caring for young. They’re strictly nocturnal, except in winter when they’re sometimes active in daytime on warm days. Many people have seen opossums 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, movement is usually a shuffling, clumsy-looking waddle, but if circumstances compel them, they can run at about 4 miles per hour — equivalent to a fast walk for a human. They 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 swim (they’re able swimmers). Or they may drop “dead.”
Opossums are well-known for feigning death, or “playing ‘possum.” They certainly look dead, but they aren’t role-playing. Feigning death is apparently an involuntary, stress-induced nervous collapse, and it’s convincing. They fall on their side and lie still with their body slightly curled. Their mouth opens in a grimace, their tongue hangs out, they drool copiously and stare with unmoving eyes. They may defecate or discharge a foul-smelling fluid from their anal glands. They don’t respond to sound or prodding. They’re pretty convincing and oftentimes predators who don’t eat dead meat will move on. This catatonia-like state may last minutes or hours. Eventually they rouse, get up and go about their activities with no ill-effects. If they’re frightened again after awakening, they play dead again.
Opossums don’t always play dead. Instead, they may try to bluff their way out of trouble with a flash of teeth and scary hissing and snarling. But, they’re aggressive only if necessary and are, in fact, sometimes called the pacifists of the animal kingdom.
Opossums are harmless, beneficial visitors to urban yards. 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 fallen fruit and clean up leftover dog food and any munchies in the compost pile.
Although well adapted to city life, the natural habitat of opossums is deciduous forests, but they also are found in farmlands, prairies and wet areas, such as marshes and streams.
You name it, they’ll eat it, and that’s probably a factor in their survival since prehistoric times. In addition to “people food” in the garbage can and pet foods left outdoors, opossums eat insects, fruits, grains, nuts, rodents, frogs, the eggs and young of other animals and carrion.
Cover and nesting
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 piles, woodpiles or under a porch. Even a chimney. They line nests with soft, dry materials, like grasses and dried leaves. They gather their nesting materials by mouth and then shove them under their body, where they loop their tail around them for transporting.
Females reach sexual maturity at about seven months of age and can breed about every 28 days year-round. Peak time is late December through January (February in northern areas), and to a lesser extent from mid-May to early July. After mating, males go their own way and don’t participate in raising the young.
Females typically mate only one or two times a year, each time having 8 to 12 young. Their reproductive system is bifid, meaning there are two sets of reproductive organs. (The male’s penis is also bifid). Some of the fetuses develop in a left uterus and the others in a right uterus. They have a very short gestation period — only 12 or 13 days. They’re born through a birth canal called the median vagina. After their birth, the young continue their development in their mother’s pouch (marsupium). But first they must make their way there. The newborns weigh 1/200th of an ounce — the size of a bee. Hairless and nearly transparent, they aren’t much more than embryos. Watching them crawl from their mother’s birth canal to her pouch is an edge-of-your-seat thriller.
Mothers prepare the way by licking a path through their hair for them to follow. With a swimming motion, the babies pull themselves blindly (literally, since their eyes are closed) along this path. The trek is only three or four inches, but for these little guys, it’s monumental. Treacherous, too. A sudden move by their mother and they’ll fall off and perish. The weaker babies will not make it, regardless.
Those who make it to the 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 there happens to be more than 13 babies, the extra ones will die.
Two months later and the size of a mouse, babies have 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 their 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 toes and tail. If any fall off, they make hissing sounds, and their mother makes clicking sounds in response. If she’s unaware they’re gone, however, she’ll continue on without them, and at this young age they’ll perish.
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 brush piles, 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 crosses a creek. (They can stay dry by squeezing back into her pouch, as she can amazingly seal it so tightly it becomes waterproof.)
The youngsters 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 perhaps 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.
Captive Opossums can live up to 10 years, but those in the wild usually don’t make it past their first year, because of heavy predation and vehicles.
Natural enemies of opossums include foxes, coyotes, bobcats, eagles, owls and other birds of prey; also dogs and cats. Otherwise, vehicles are their biggest enemy. It’s thought that opossums’ willingness to eat carrion draws them to roadkill and then, oftentimes, they become roadkill. Hunters and trappers, too, take a toll, but mostly by finding opossums while seeking other game.
Opossums and rabies
The body temperature of opossums is 94 to 97 degrees F., which is too low for the rabies virus to survive. It’s nearly impossible for an opossum to have rabies.
*Top photo: Lisa Wright / EOL; cc by-nc-sa 3.0
¹Ancient origins of modern opossums revealed
²For the curious: African Elephants have the best sense of smell, with 1,948 olfactory genes. See the Top-10 list
³Before considering whether to keep a wild animal as a pet, read this: Wildlife cute, but not good pets
Virginia Opossum at a glance
Appearance: Long, pointy white face; small, dark ears tipped with white; pink nose. Body hair sparse, grizzled. Long, hairless, rat-like tail.