Window on Nature
By Lowell & Kaye Christie, F47246
Opossums (Didelphis marsupialis) are the only marsupials (pouched mammals) native to North America, and they’ve been around a long, long time. Unfortunately, we’ve seen far more opossums dead than alive. They have a habit of feeding on roadkill in the middle of the night, completely oblivious to approaching cars. The fact that they aren’t smart enough to get out of the road only reinforces their reputation as being dim-witted animals.
Paleontologists have traced the opossum family line back more than 65 million years. At that time many species of marsupials existed; most are now extinct, replaced by placental mammals such as horses, camels, and dogs. Australia now has the most marsupial species, which include kangaroos, koalas, wallabies, and Tasmanian devils. At least we still have our opossum in North America.
An adult opossum is approximately the size of a house cat. Its head is usually white, with a long pointed snout, a pink nose, shiny black eyes, and a pair of naked black ears. It has 50 teeth, the most of any mammal, and all of them are needle sharp. The body is covered with coarse gray hair; the legs are usually darker in color. Opossum feet are designed for climbing, with toes that grasp like human fingers. As for the tail, it’s naked, scaly, and strong enough for the critter to wrap around a tree for assistance while climbing. (An opossum can hang from its tail, but not for very long.) The tail does come in handy for holding leaves, twigs, and grasses that the front paws have gathered and passed under the hind legs.
When the first Europeans arrived in North America, the opossum’s range was limited to the southeastern United States. Like the cattle egret we investigated last month, opossums have spread throughout much of the United States and have taken up residence anywhere they can find their required habitat.
Since opossums don’t hibernate, their northern range is limited by winter temperatures. Arid deserts aren’t suitable either, so you’ll rarely spot one in the southwestern deserts, but they are plentiful in the Pacific states and are said to range as far south as southern California.
On the whole, opossums prefer living in deciduous woodlands and shrub thickets, but they also inhabit prairies, marshes, farmlands, small towns, and sometimes cities. Any place will do as long as food is present and it isn’t too cold or too dry.
Our subjects also need den sites, but they’re not very choosy about where they set up residence. As long as it’s dry, safe, and sheltered from the elements, opossums don’t care whether it’s a hollow tree, a log, or a brush pile.
For the most part, opossums are nocturnal animals. In colder climates or seasons, they may have to leave their dens to prevent frostbite, or worse. Since the animals don’t store food, their appetites urge them out to look for insects (grasshoppers, crickets, beetles, etc.), as well as earthworms, small rodents, small birds, and rabbits. They’re quite willing to dine on crustaceans, too, if they’re available. Opossums even eat poisonous snakes; luckily, they are immune to the venom. Opossums aren’t strict carnivores “” they’ll harvest fruits and berries in the summer. In human territory, they turn into scavengers, turning over trash bins or stealing produce from gardens.
When moving through an open field or an unprotected area, opossums must be cautious to avoid predators. They are slow animals, and the best way for them to escape danger is to climb a tree. Failing that, they may whip around, bare their teeth, and hiss or snarl when confronted. Drooling is another tactic the animal will use to ward off a threat. Predators often associate heavy drooling with disease, and abandon the pursuit.
When an opossum actually is attacked, it drops to the ground, excretes a foul odor, and “plays possum.” This is an involuntary state of unconsciousness triggered by extreme fear. For many predators, the “kill” is part of the stimulus to eat; thus, it turns away from the motionless critter. The opossum is actually out cold, but when it recovers and sees that the danger is gone, it gets up and moseys off.
Opossums breed in the same manner as other mammals, but the females are pregnant for only 13 days. At birth, the partially developed babies are but a half-inch long and weigh about as much as a dime. Their mother doesn’t collect them and drop them into her warm, fur-lined pouch. Instead, she licks her fur in the direction of the pouch, thus creating a path that the newborns follow.
Upon arrival, each baby finds a nipple and attaches to it. A month and a half later, the youngsters begin to open their eyes and release the nipples. When they are about the size of a house mouse, they begin to leave the pouch for short periods of time.
Litter size varies from five to a dozen offspring; the average is nine. If the litter is large, the pouch may not be sufficient to hold all of the young once they start growing, so some begin riding on their mother’s back. It won’t be long before the babies are large enough and strong enough to venture out on their own.
Life is full of hazards for opossums. Mortality rates are high at all stages and ages. Even in the pouch, the mortality rate is 10 to 25 percent. Only a few adults live longer than a year, and even the lucky ones survive a mere 2-1/2 to 3 years. That’s not their biological limit, though; zoo animals sometimes live for a decade.
As for opossums being stupid … yes, their brains are smaller than other mammals of a similar size. But these critters are smart enough to climb into a trash bin in search of food, and you can bet they’ll find and eat pet food left out overnight. If only they could remember to look both ways before crossing the road.