New World Opossums: Didelphimorphia

Physical characteristics: The Virginia opossum is one marsupial that a majority of Americans have surely seen, if only as roadkill. These opossums have low-slung, vaguely rat-shaped bodies that in adults can weigh up to 14 pounds (6.4 kilograms). Males are larger than females. Adult head and body length can reach 20 inches (50 centimeters), and the tail length can reach 18 inches (47 centimeters). The body fur is light to dark grayish, due to a coat of white fur with black tips under a longer coat of pale guard hairs. The head is white and elongated, and studded with long whiskers. In some individuals, the gray coat may extend in a stripe across the crown, tapering to an end between the eyes. The eyes are black and shiny. The long, strong tail is scaly, colored whitish or pinkish, and nearly hairless, much like a rat's, and is prehensile, able to grasp tree branches Virginia opossums can eat poisonous snakes. They are immune to the venom of these snakes, including copperheads, water moccasins, and rattlesnakes. (Illustration by Jonathan Higgins. Reproduced by permission.) and carry nesting materials. The ears, nostrils, forepaws, and hind-paws are pinkish and only sparsely furred. Each paw has five digits, and the hallux (HAL-lux; big toe) is opposable, allowing the opos-sum to grasp branches.

Geographic range: The Virginia opossum is one of the few marsupials, in Australasia or the Americas, that is at home in temperate regions with cold winters. Its range extends as far north as Ontario, Canada, and as far south as Costa Rica in Central America. Virginia 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.

Habitat: Virginia opossums prefer living in forest, farmland, and suburbia with possible denning sites and a water source close at hand, but this adaptable species can survive and thrive almost anywhere, including grassland and near-desert conditions. These opossums are nomadic, seldom staying in one foraging area for more than a year. Individuals may sleep during the day in whatever temporary shelters they find, or build nests, lined with leaves. Refuges include woodpiles, thickets, rock crevices, and in various human-made structures such as under porches and raised houses, and in barns, drainpipes, and sheds.

Diet: The Virginia opossum is truly omnivorous, eating almost anything that can be considered food. A partial list of dietary preferences includes rats, mice, moles, slugs, snails, shrews, worms, beetles, ants, grasshoppers, crickets, frogs, garbage, fruit, corn, berries, and carrion. An even more unusual source of food is poisonous snakes, to whose venoms the opossums are immune. This includes copperheads, water moccasins, and rattlesnakes.

Behavior and reproduction: Like most opossums, Virginia opossums live and forage, search for food, solitarily. They forage mostly at night, but sometimes during the day. If male individuals meet, they avoid each other or sound off with threat displays, with hissings, growlings, and screechings, often going on to one-on-one combat. Males fight one another ferociously during mating seasons. On the other hand, if a male and female meet during the breeding season, they will mate and then stay together for several days.

Mating seasons vary according to how far north individual opossums live. Virginia opossums begin mating in December in the southern states, in March in the northernmost states and Canada, and in January and February for areas between. In Canada and in the north and central states, females usually bear only one litter per year. Two or even three litters are common in the southern states and further south.

Young are born thirteen days after mating. Litters can range in numbers of up to twenty, with a record of fifty-two, but since the mother has only thirteen nipples, only a maximum of thirteen in a litter can survive. Newborns are scarcely bigger than rice grains. The young spend up to 100 days, or slightly over three months, in the pouch. By seventy-five to eighty-five days, the young are weaned and leave the pouch, but remain with the mother for another two or three months before leaving to live on their own. Until they leave, the mother carries the young on her back. Young males reach sexual maturity at eight months, females at six. The longest recorded lifespan in the wild for the Virginia opossum is three years, although captive individuals have lived as long as ten years.

When threatened by a predator, a Virginia opossum may react in any of several ways. Escape is always the optimal choice, and includes climbing trees and swimming. If escape proves impossible, the opossum may use its variation of the basic mammalian threat response, opening its jaws wide, baring its fifty-five teeth, and hissing at its foe. It may also discharge a foul-smelling, greenish fluid from anal glands. Or, the opossum may use its "drooling" display, building up its saliva content, drooling from its mouth and blowing froth and bubbles from its nostrils, in hopes of convincing a predator that the opossum is seriously diseased and therefore dangerous to eat.

The opossum's final defensive recourse is either fighting back or performing its most famous behavior, "playing possum." The animal collapses, the eyes glaze, the jaws open, the tongue lolls, the teeth are partly bared, and the stinky anal fluid release adds the final carrion touch. The deathlike state is a form of catatonia, in which the animal lies limp, does not react to touch or prodding, and cannot be roused by any method. The muscles become limp, basic functions slow. Predators of opossums, among them coyotes, dogs, bobcats, and birds of prey, will reject the seemingly dead opossum and leave it untouched. From one minute to six hours after the predator has left the scene, the opossum rouses itself and moves off.

Throughout its range in Canada and in parts of the United States that have long, cold winters, Virginia opossums feed to build up extra body fat in the fall in preparation for the lean winter months. The species doesn't hibernate, but in especially cold weather, individuals may stay quietly in their shelters for a few days. Otherwise, they're outside and hiking across the snow to forage.

Virginia opossums and people: Virginia opossums sometimes help themselves to human garbage, but cause far less mess and destruction than do raccoons. Virginia opossums, like most mammals, can carry and transmit rabies. Virginia opossums have been, and still are, hunted for food and for their pelts.

Their ability to eat almost anything organic puts Virginia opossums in the front ranks of living nature's cleaning crews. They eat pest insects like cockroaches, garden pests like snails and slugs, pest mammals like roof rats and mice, and they eat all varieties of carrion.

Conservation status: Virginia opossums have adapted to humans successfully, are in no danger of extinction, and have even extended their ranges in some areas. ∎