The opossum (properly, the Virginia opossum—Didelphis virginiana) is the only marsupial found north of Mexico. Marsupials are distinguished by their unique mode of reproduction: The young are born in an almost embryonic form and make their way to the pouch in their mother's abdomen, where they are nourished for what in other mammals would be most of the gestational period.

Opossums are found throughout much of the United States and north into parts of southeastern Canada. Like other mammalian generalists common in urban and suburban areas—animals such as raccoons and coyotes, who aren't picky about what they eat—opossums have thrived despite human alterations to the landscape.

The opossum is a medium-sized mammal about the size of a house cat, with long guard hairs that give their fur a very coarse appearance. Their coat color varies from light—almost white—to almost black, but usually looks gray. Opossums also have naked ears and a long, almost hairless, prehensile tail, which is capable of grasping and holding objects. While the tail might support the opossum's full weight for brief periods, the animal usually uses at least one foot as well as the tail when dangling from a limb. Perhaps because of their naked tails, opossums are often mistaken for rats.

When confronted, opossums sometimes display their teeth (opossums have more teeth—fifty of them—than any other North American mammal) and may even hiss. Although this appears to signal a fierce opponent, opossums are actually shy and inoffensive. Rather than fight, they'll sometimes slip into a state of apparent death—a reaction celebrated in our colloquial expression, "playing possum." This state of catatonia can last a minute or two, or even as long as two hours, before the "dead" opossum revives and moves on, once the danger has passed.

Opossums are omnivorous and consume an amazing variety of plant and animal foods. Invertebrates, such as insects, slugs, snails, and worms, can comprise a large part of their diet, and they're not above scavenging carrion. Contrary to popular folklore, opossums very rarely raid garbage cans, poultry coops, or gardens. They are most active at night, and they have a habit of ceaselessly moving along the ground in search of food, without following trails or travel routes to places of known food sources. In fact, adult male opossums may wander continuously. Females spend their lives in more defined areas, but still move around almost randomly. Most opossums seen in yards and neighborhoods are likely to move on without human encouragement or intervention if given enough time.

Opossums may breed twice a year and give birth to as many as 12 young, to overcome the high mortality rate that most opossum populations face—the average female opossum probably lives only a year. Young emerge from their mother's pouch at about 1–2 months of age, then ride on their mother's back. They become independent at about three months. Excellent climbers, opossums may take shelter by day in tree dens, old squirrel nests, or nests they've built themselves above ground. They can also make homes under decks or patios, and in wood- and brushpiles.

Problems and Solutions

Opossums are undoubtedly more beneficial to humans as consumers of undesirable insects, snails, and slugs than they are harmful to people for any damage they cause. If you see an opossum in your yard and wonder what, if anything, you should do, the best reaction is patience. The animal will likely move on in short order and should not be a threat or concern. Where an opossum is known to den under a porch or patio, the eviction strategy is much the same as for skunks (click on "Solving Problems with Skunks" below). While it is unlikely that they'll plunder your garden or trash cans, the most effective methods for discouraging visits by opossums or other urban wildlife are to secure trash containers with tight-fitting lids, secure pet doors at night, and pick up food bowls at night if pets have been fed outdoors.