Woe be the lowly opossum; the Rodney Dangerfield of the mammal community.† Itís not that they donít deserve it.†
Opossum are the only marsupials in North America, migrating north from South America when the land bridge between the two continents was formed some 3 million years ago.† They are, in fact, a more primitive mammal than placentals.† Opossums, like the more primitive monotremes (echidna and duck-billed platypus), and some shrew, have only a single opening, or cloaca, closed by a sphincter muscle into which all of the fecal, urinal and genital products are discharged.† This characteristic is shared with reptiles and birds.
They also have a less efficient reproductive process than the placental mammals.† Records exist of females with as few as 9 or as many as 17 teats.† Additionally, not all mammae are functional.† Males have a forked penis, which matches the paired lateral vaginae of the female. In other more advanced mammals, the female reproductive tube fuses in the middle to form a single canal. In fact, the opossums produce paired sperm.† As a pair, the sperm swim in a straight line, but if separated, they swim in circles.† Copulation involves the male grabbing the female by the nape of the neck and both falling over to the right side. On occasion when they may fall to the left, or remain upright, copulation is likely to be unsuccessful.† I donít make this stuff up.
At the time of European arrival in North America, opossum were limited to south of the Potomac River to Harpers Ferry, and on a line to Wheeling, then northwest including most of Ohio, Indiana and Illinois.† With the removal of natural predators, they have moved north since that time and now reach Canada.† Itís not hard to find opossum in northern regions suffering from frostbitten ears or toes.
One might say their omnivorous diet is somewhat primitive as well.† Carrion, with maggots, is a year-round treat.† In fact, in baited traps in the Smokies, more opossum were caught with decomposed bait, rather than fresh bait.†† Strangely enough, they can also eat rattlesnakes, copperheads and water moccasins due to their apparent immunity to pit viper venom.† They have even been known to eat toxic American toads.† And, in the category of more than you wanted to know, if you come across a partially eaten deer carcass in the woods, the entrance via the anal area would be the work of an opossum.
Opossum are terribly near-sighted (one reason for so many road-kills). Also, when frightened, they freeze, or feign death (not effective against cars). Finally, they are often along roads looking for food in the form of road kills---often other opossum.
For more on the opossum or other Appalachian mammals, go to www.bobpickett.org.
North America's only marsupial (female has a pouch) mammal. The female carries and nurses her young in her marsupium until they are about 2 to 3 months old; then they are carried on her back another 1 to 2 months whenever they are away from the den.
Size of a cat; grey to black fur; black eyes; pink nose, feet and tail; black ears; and pointed nose.
Solitary and nocturnal: usually slow moving; when frightened and unable to flee may fall into an involuntary shock-like state, "playing 'possum".
Hiss or growl and show their 50 sharp teeth when frightened; but, in reality, they are gentle and placidó they prefer to avoid all confrontations and wish to be left alone.
Omnivorous: eats insects, snails, rodents, berries, over-ripe fruit, grasses, leaves, and carrion; occasionally will eat snakes, ground eggs, corn or other vegetables.
Adaptable; able to live wherever water, food, and shelter exist. At home in trees; uses its prehensile tail to help stabilize position when climbingó it does not, however, hang by its tail.
Few live beyond the age of 1 year in the environment; rare reports of living 5 to 10 years in captivity. Killed by many predators: humans (and cars), dogs, cats, owls, and larger wildlife.
It does not have a territory, but is always on the move, going to wherever the food is. Females stay in a smaller area while they care for their young. They seem to have a naturally high level of immunity to most diseases. Example? Opossums are more resistant to rabies than any other mammal; cattle, goats, dogs, cats, sheep, and the ice cream man are far more susceptible to rabies!
Vernon Bailey, a former naturalist with the U.S. Biological Survey, decided to measure the brain capacity of a number of common animals by filling the brain pans with beans. The number of beans necessary to fill a ípossumís brain chamber was 21. In comparison, Bailey recorded the following number of beans for other animals: skunk, 35 beans; porcupine, 70; raccoon, 150; red fox 198.
Other scientists, however, have found evidence that opossums do not deserve the "dim-witted" label. Researcher William James of the University of Georgia, for instance, discovered that opossums were better at remembering where food was hidden in a complicated maze than were dogs, cats, rabbits or turtles. In fact, only humans were clearly superior to them in such studies. Cornell University researchers, meanwhile, discovered that opossums learned quickly how to distinguish between toxic and edible mushrooms, even though the plants used in the study were nearly identical in appearance.
Intelligent or not, opossums clearly are adaptable, which is why they have survived for more than 50 million years, far outliving such creatures as the saber-toothed tiger. During this time, their instinctive behavior has helped them cope with adversity. For example, when attacked by a predator, opossums often roll over and play dead, putting themselves into a stupor, rather than try to outrun their enemies. "Playing ípossum" has worked well against aggressive predators, but unfortunately not so well against oncoming cars.
The opossumís reproduction system may be its true trump card for survival. Though courtship among opossums is nearly nonexistent, the result of a pairing is incredible. After only 12-1/2 days, the shortest gestation of any North American mammal, the female bears a litter of about 16 youngsters--hairless, pink grubs so small that all 16 could fit easily into a teaspoon. But for these youngsters, being born is easy compared to the life and death journey from the motherís womb to the pouch on her belly.
Blind and with only two working legs, and no help whatsoever from the mother, a newborn opossum begins its toughest struggle for survival. Entirely on its own, the youngster must laboriously drag itself up to and into the marsupium three inches away. Some do not make it, and some of those that do complete the journey cannot find a nipple inside, and they also perish. Though 16 to 18 are born, the average number of young opossums raised in the pouch is only nine. But with two litters a year, there are plenty of opossums around to saunter across backyards, crawl into garbage cans--and lick up fallen birdseed on cold winter days. --George H. Harrison
The uniqueness of the opossum makes him a valuable member of our wildlife community. He has more teeth (50) than any other American land mammal, and puts them to good use eating cockroaches, moles, crickets, snails, rats, mice, overripe friut, and dead animals of all types. He is more immune to many diseases (including rabies) than your neighbor's dog or cat, and even has a remarkable resistance to poisonous snake bites.
†† "Playing Possum" is one of the most effective ways the opossums defends itself. When unable to flee, extreme fear places the opossum into an involuntary coma. They become stiff and their mouths will gape open. This condition will last 40 minutes to 4 hours. Most predators will abandon their attack, once the opossum is thought to be dead.
You will not see opossums being born. At birth 20 can fit into a teaspoon. You will see infant opossums at about three months of age, riding on mothers back or in or near her pouch. If you see a mother with babies, be very quiet, if you spook her she may dash off and drop a baby. She will not come back for it and unless you rescue it, it will perish. If you see a large opossum on the road that has been hit, you can check to see if there are babies still in her pouch or around her body. Often in the spring, mother who have been hit will still have babies that have survived and can be rescued. The opossum is not a hibernating animal but it will hole up in a hollow log or a crevice among the rocks during a cold spell. It is an extremely tough and adaptable animal, if somewhat slow. Opossums have opposable thumbs on their hind feet which help them to grip branches and climb. They are the only non-primates with opposable thumbs.
Opossums have the most teeth of any North American mammal.
Opossums are found in North America, from Central America and Mexico in the south, through the United States east of the Rocky Mountains and north into southwestern Ontario. Opossums are also found along the west coast of the United States. Their range appears to be expanding northward (McManus, 1974).
Virginia opossums rarely live for longer than 18 months. The oldest known opossum in the wild was 3 years old when last captured. Although they are preyed upon by several predators, most are killed by cars.
When America was first colonized by Europeans, these possums did not occur north of Pennsylvania. As time passed, they moved north and westward on the Great Plains. In 1890, they were introduced to California. They spread on the west coast. Today in Michigan, they are currently spreading into the Upper Peninsula.
Opossums are living fossils, the oldest living mammal on this continent. Paleontologists have learned that while dinosaurs still roamed the huge land mass known as Gondwanaland, the first mammals that evolved were opossum-like marsupials (pouched mammals).
When Gondwanaland began to separate, Australia drifted down under with its now-famous marsupial critters. South America also sailed away into isolation for millions of years, while a whole slew of marsupial species evolved.
Somewhere between two to five million years ago, North America and South America met up again, opening a super-highway for wildlife traffic in both directions. Only one marsupial managed to go northward, the common opossum (Didelphis marsupialis). It developed into a new species, the Virginia opossum (Didelphis virginiana), which settled in what is now the southeastern United States.
Twelve and a half days later (the shortest gestation period of any North American mammal), the mother sits up and licks the fur on her belly then gives birth to about 20 not yet fully-formed babies. Each is about half an inch long. They are blind, deaf, and barely functioning, except for a strong mouth and two front feet which "swim" up the wet pathway into her pouch.
Once inside the furry pouch, each of the 13
luckiest (and strongest) babies attach themselves to one of her her 13 nipples,
which become their lifelines for the next two months.
At two months, when the youngsters have grown from the size of a bee to the size of a chipmunk, their eyes finally open. They cautiously peek over the pouch opening and finally venture outside, usually pulling their nipples out with them. Imagine poor, patient momma with thirteen nipples being stretched in thirteen different directions!
In another week or two, with their little tails and hands (yes, hands, with opposable thumbs!) clutching her fur, the whole family rides around on momma's back (sans nipples) for a few weeks while she forages. If she needs to cross a stream, all the babies pile back inside. Momma tightens up her pouch muscles and keeps the babies dry.
Later on, the gray and white babies, which grow to house cat size (6 to 12 pounds), use their prehensile tails for stability while climbing trees and for carrying nesting material. The only opossums who hang by their tails are in cartoons!
Some of the other adaptations include the New World opossums, which have a clawless, opposable hallux (the big toe) on the hind foot which they use much like a thumb to gain a foothold in the trees, since they are arboreal in habit.