Misplaced Marsupial

The Adaptable VIRGINIA OPOSSUM, a Misplaced, Mischievous MARSUPIAL, Thrives in the Desert

IT'S NO SURPRISE TO GLIMPSE LONG-tailed, bewhiskered, water-loving opossums ambling along back roads in swampy areas of the southeastern states. However, not many think of this robust marsupial as a resident of the arid Southwest - hanging upside down with an idiot grin from the prickly arm of a saguaro. But the opossum thrives in an astonish ing variety of Arizona's sometimes harsh envi rons. Then again, survival is the opossum's specialty, as it's the only marsupial species to live in North America. Broad tastes, a weird thermostat, an improvised thumb and a useful stink serve the opossum well.

Some experts say S.M. White of Tempe first introduced Virginia opossums (Didelphis virgini ana) to Arizona in 1927 with releases near Tucson and in the White Mountains of the east central part of the state. Others believe the resourceful critters migrated here from Mexico.

Either way, opossums have happily settled in Arizona, and it looks as though they're here to stay.

"[White] dearly loved opossums," said Randy Babb, a biologist and an information and edu cation program manager with the Arizona Depart ment of Game and Fish. White, a transplant to Arizona from his native Arkansas, decided that if he could move, so could his beloved marsupial. And so he became "the Johnny Appleseed of opossums," liberally releasing the mis-chievous critters in southern Arizona.

But opossums also have hitched rides west on their own. Babb related a recent tale of a young male in Kentucky that ambled under the cover of darkness into a truck filled with shopping carts. Several days later in Arizona, the opossum was discovered when the truck was unloaded. "They pop up with an alarming degree of regularity where they don't belong,' Babb said.Studies show the Virginia opossum has expanded its range northward and westward within the past century, multiplying throughout the United States. Its appearance varies markedly from region to region - a grizzled gray in the North and darker-featured in the South.

The Virginia opossum can lower its body tem perature during freezing weather and become dor mant, though it doesn't truly hibernate. This cosmopolitan carnivore has a highly opportunis tic attitude toward food and dines on insects, birds, reptiles, amphibians, eggs, earthworms, small mammals and carrion. In a pinch, it munches on fruits, plants, grains, mushrooms and acorns. Nearly everything rates as welcome fare for this survivor.

When these dietary generalists show up around civilization, trouble is sure to follow. They are likely to end up on a front porch to eat from a cat food dish, climb orange trees for their fruit or land headfirst in a garbage can. Then they might curl up in a garage or attic to sleep for the day. "They can hold things, open stuff, pry the lid off a box and take off a trash can lid," said Babb. "Because they are so dexterous, they can get into quite a bit of mischief."

Of the 77 opossum species found in the Western Hemisphere, the Virginia opossum is the largest, measuring an average of 43 inches in length half of it tail. The animal's front feet have five clawed toes. Its hind feet have four clawed toes, with the fifth clawless toe acting as an opposable thumb.

The opossum's long, sleek gray hair and its soft, woolly undercoating were once prized as fur for apparel. Nowadays the opossum isn't losing its skin to the fur trade, but its meat is still considered a delicacy in the South.

Mostly nocturnal by nature, the roving Virginia opossum usually sleeps in a borrowed burrow by day and hunts all night. Although the young can sometimes be seen hanging from trees by their tails, adult opossums are too heavy to support their weight in this manner.

Like all marsupials, the Virginia opossum grows its embryolike young in a pouch instead of a womb. A female opossum typically has 13 nip ples and an average litter size of seven to nine. After a two-week gestation period, the newborn opossums, about the size of kidney beans, wiggle their way from the birth canal, up across their mother's belly and into the pouch, a distance of about 3 inches. Once they successfully make the trip, the newborns spend about 2 months in the mother's pouch attached to the nipples - a period equivalent to the gestation period of any mammal of the same size. About another month will pass with the young occasionally taking short trips out of the pouch before being weaned.

However, the opossum doesn't display much maternal behavior and only cares for its young while they're in the pouch. The babies are on their own about 100 days after birth. The opossum has underdeveloped "social skills" and is launched by instinct into a dangerous, solitary life. The Virginia opossum's habit of feigning death when threatened gave rise to the expression "playing possum." However, the creature's builtin defense mechanism when faced with danger - becoming immobile, slack-jawed and fetid actually puts the animal into a torpid state. It then emits a stench that convinces most predators it's been dead long enough to make an unhealthy meal.While appearing dead, the temporarily catatonic critter has a reduced sensitivity to tactile stimulation and can be poked and prodded without responding. It may remain in this state for as long as two hours before rolling over and continuing on its merry way.

Some people have succeeded in taming opossums, although the animals' lack of intelligence limits their learning potential. Their primitive brains measure about one-fifth the size of an average house cat's. The sturdy marsupials also have a low taste sensitivity, which is why they can eat just about anything.

Scientists believe that the Virginia opossum bears a close resemblance to ancestral mammalian stocks. The opossum's ancestors roamed the Earth with dinosaurs, and marsupial fossil remains date from as far back as 70 million years, during the Cretaceous period.

However, the Virginia opossum didn't show up in North America until the latter part of the Pleistocene period, 150,000 years ago.

And they're still on the move, occupying even unlikely desert environments sort of like good old Homo sapiens.

So maybe there's a lesson in this for us. Maybe it's all right to have a small brain and a bad stink so long as you've got opposable thumbs and aren't a picky eater. All