Years ago, when we owned a dog, we fed him on the back porch. One early April evening we heard a commotion outside. I opened the kitchen door and saw Fritz sniffing at an opossum, which was laid out flat on its side, its eyes tightly shut, its mouth stretched in a gruesome grin that exposed its front cheekteeth, and its tongue lolling. While I knew about “playing possum,” Fritz did not, and he looked as puzzled as a dog could. I called him into the house and watched from the window for over ten minutes until the opossum slowly roused itself, remained still for another couple minutes, and then ambled away, none the worse for its encounter.
More recently, opossums come to our back porch on late winter and early spring evenings for spilled birdseeds and usually shamble off instead of playing dead if I open the door. They also like to visit our compost pile for tasty tidbits.
By April, those that have survived the winter are not only very hungry, especially if it has been unusually cold, but if they are females, they are already carrying little ones in their pouches. Most studies show that opossums cannot survive outside if the temperature dips below 19 degrees Fahrenheit, so they spend those cold days and nights tucked in a warm den that once belonged to a woodchuck or other burrow-digging animal. They line it with grass and leaves, which they gather by grasping them in their mouths and then passing them under their body to their tail. They use their tail to transport the materials to the den, a behavior that even youngsters at 88 days of age can master.
However, they don’t hibernate so if they can’t go out, they don’t eat. And if they lose more than 42% of their pre-winter body mass, they starve to death. One researcher calculated that opossums could spend no more than 70 winter days in a den before they might die, and they needed at least 50 winter days to forage in order to make it through the winter. However, those 50 days had to be well-spaced throughout the winter. Furthermore, the more fit an opossum is when winter begins, the more likely it is to survive.
Despite such dire predictions, opossums have managed to expand their range 500 miles northward in the eastern United States since the Colonial Era. Before European settlement, they lived no farther north than Kentucky, Indiana and Ohio. Today they are found as far north as Wisconsin, Michigan, New York and southern New England. But in those northern areas, they are liable to be suburban and urban residents where garbage and fruit-bearing shrubs and trees are readily available, according to a study by L.L. Kanda in Amherst, Massachusetts.
Opossums are renowned for their small brains, which humans have equated with stupidity. Not so, say some scientists, including Steven Austad, who designed four runways, only one of which was connected to a food box. Of the cats, chicks, dogs, goats, pigs, rabbits, rats, turtles, and opossums that he tested, opossums scored highest in their ability to remember where the food box was.
Another researcher, Scott Camazine, when he was at Cornell University, fed opossums poisonous mushrooms that they not only quickly tasted and rejected but remembered as bad food for as long as a year.Penn State ecologist Richard Yahner, in his book Fascinating Mammals, says that…”based on some learning and discrimination tests, some scientists go as far as to contend that the intelligence of Virginia opossums is higher than that of dogs and equal to pigs…” At least as far as their tummies are concerned.
The Virginia opossum, also called “white face,” is one of 70 extant possum species, but the only marsupial that lives in North America. Yet 35 million years ago at least three families, five genera, and 13 species of marsupials lived here. In fact, some scientists believe that marsupials may have originated in North America and most certainly in the Western Hemisphere. But for unknown reasons, marsupials became extinct in North America 15 million years ago, even while they continued to radiate successfully in Central and South America as well as in Australia and New Guinea in the Eastern Hemisphere. Today our hemispheric southern neighbors have close to 80 marsupial species or 30% of the world’s marsupials.
About 75,000 years ago, our Virginia opossum (Didelphis virginia) diverged from its ancestral species, the still flourishing common possum of northern South America (Didelphis marsupialis). One of three species in the genus Didelphis, which is Greek for “double womb,” the third is Didelphis albiventris, the white-eared opossum of southern South America.
Because the explorer John Smith in 1612 first saw the Virginia opossum in Virginia, its species’ name is virginiana. “An Opassum,” Smith wrote, “hath a head like a swine and a taile like a Rat, and is of the Bigness of a Cat.” The name “opossum” comes from the Algonquian “apasum” meaning “white animal,” even though opossums are mostly gray except for their cone-shaped faces. Young opossums, with their bright, black eyes, perky, dark, shell-like ears, and pink noses are apparently endearing to some people, and the National Opossum Society of Catonsburg, Maryland sells a variety of opossum-themed items to what appears to be an expanding fan base for opossums.
But their long, naked, rat-like, prehensile tails that allow them to hang from trees repulse other people. They also show unbecoming signs of old age such as cataracts, weight loss, ears shriveled from frost bite, and lack of motor coordination by the time they are two years old. Those females that are still alive have atrophied reproductive organs. This leads to smaller litters, more female than male young, and often the inability to conceive at all.
For their size-on average four to ten pounds-opossums are incredibly short-lived mammals. But during their reproductive span, they are also incredibly prolific. Here in Pennsylvania, opossums usually have two families a year-in late February or March and June or July.
Males continually make a clicking sound when pursuing a female, the same sound they make in aggressive encounters with other males and that females use in communication with their young. Even though males have half as many sperm as other mammals of their size, their unique, forked penises deliver spermatozoa to the paired uteri of the females during mating, which lasts 20 minutes.After only a 12-to 13-day gestation period, as many as 25 tiny young are born to the sitting mother, her neck arched and her head down. Although they are the size of raisins and are blind, deaf, pink-skinned, and hairless, these “living embryos” have well-developed front legs and sharp claws. Using legs and claws, they climb hand over hand in a swimming motion up the belly hair of their mother and into her pouch–a distance of two inches which takes them about 16 and a half seconds. Not all of them make it and those that do find only 13 nipples to grasp. Once a youngster grabs a nipple, it enlarges and forms a bulb inside the young one’s mouth that remains attached for two months. Within a month, only seven or eight youngsters survive in the pouch, probably because not all the nipples are fully-functional. During that time, their mother moves from den to den and from food source to food source all the while her young are nursing.
Their eyes open at 58 to 72 days of age when they are able to climb out of the pouch. Then they grab their mother by her fur and ride on her back for another two to four weeks. During that time they eat some solid food, and at 100 days of age they are weaned and on their own. But most stay in the brushy vicinity of their weaning den for several months, where they have learned about food sources from their mother, before moving from den to den as adults do. Nevertheless, less than half the youngsters survive the rigors of food-gathering and predator-dodging.
Opossums are mostly abroad at night, foraging in brushy edges or along small permanent or intermittent streams such as our stream. John Seidensticker, who followed radio-collared opossums in Virginia’s Blue Ridge Mountains, discovered that rural opossums would trek to new foraging areas night after night. Females, even with young in their pouches, traveled as far as a mile or more. Males ranged even farther and faster. On average males covered 25 acres on a summer night and females ten acres. But in suburban or urban habitats, where garbage is readily available, opossums may never move.
In the country they eat insects, small mammals, fruits and berries, especially blackberries, apples, and persimmons, amphibians, earthworms, birds, green vegetation, bats, carrion, and snakes, including rattlesnakes, copperheads, and water moccasins because opossums are immune to Western Hemisphere pit viper venom. In parts of Texas, six percent of their diet consists of copperheads.
Opossums, in turn, are eaten by dogs, great horned owls, coyotes, foxes, bobcats, raccoons, and raptors. Most deadly of all, though, is the automobile, especially when an opossum is feeding on road-killed carrion. We often surprise opossums on our road when we are driving home at night and inevitably we must stop and wait patiently until they find their way off the road.
They rely on their super-sensitive noses to find food, and biologist Donna Holmes, who studied captive opossums, discovered that they excrete strong odors, which they use to mark their home range and signal prospective mates. They also follow their noses in search of dens and escape routes.In addition to clicking, opossums hiss, growl, screech, and bare their teeth when defending themselves or encountering other aggressive opossums. They even sometimes extrude a greenish substance from glands near their vent, especially when they are playing dead, but scientists do not know what it is or why they do it.
Altogether, opossums are remarkable animals as Seiedensticker discovered during his five-year study. “I assumed,” he wrote, “they were slow and simple creatures… [but] the supposedly primitive opossum turned out to be a lot more efficient and sophisticated than I had anticipated.” Feeding and breeding, he concluded, are what they do best. Because of their single-minded pursuit of food and their efficient breeding system, they have been able to not only survive but thrive in a wide variety of habitats.
Opossum illustration courtesy of U. S. Fish and Wildlife Service/Bob Savannah