Virginia Opossum

Also known as

Opossum, possum

What is the scientific name?

Didelphis virginiana

• Pronounced di-DELL-fis vir-gin-ee-AAN-a
• What does it mean? "Virginia two-womb." Didelphis is from two Greek words, di meaning two or double and delphys meaning womb. This refers to the opossum's fur-lined pouch (marsupium) which acts as a secondary womb. Virginiana is the Latinized form of the state of Virginia, source of the first scientifically described opossum.

Where are they located? How many subspecies are there?

Opossums are found throughout most of North America, from southern Canada to Mexico. While originally restricted to the eastern United States, they have continued to expand their range both west and north (Gardner, 1982). There are four subspecies of opossum, but only one that occurs over most of the United States: D.v. virginiana (Gardner 1982; McManus 1974).

Where do they live?

The opossum prefers deciduous woodlands near water, but can be found in a variety of habitats including marshlands, forests, farmland, and residential areas (Gardner 1982).

What do they look like?

Opossums are gray with long pointed noses and hairless ears and tail. The tail is "prehensile," which means it can be wrapped and folded around objects like a tree branch. While certain monkeys have prehensile tails and use them to hang from, opossums don't normally hang by their tails (Nowak 1991).

How big are they?

The head and body length is between 13 and 20 inches; tail length is between 10 and 21 inches (Maser et al 1981). Males can grow up to a total length of 37 inches; females to a total length of 36 inches (Hall 1981). Males can weigh between 1 and 13 pounds, but average around 5 pounds. Females weigh between one-half and 8 pounds, but average about 2 pounds (Gardner 1982).

How long do they live?

The average life expectancy is one and one-third years (Petrides 1949), but even this is thought to be a high estimate (Gardner 1982). The oldest recorded opossum in the wild was about three years old (Gardner 1982). In captivity they can live between four and five years (Gardner 1982).

What do they eat?

Mostly insects and carrion (McManus 1974), but the opossum is omnivorous, eating a variety of animal and plant matter. The diet includes: grasshoppers, slugs, caterpillars, mice, frogs, shrews, snakes, bird eggs, corn, chestnuts, acorns, blackberries, wild cherries, persimmons, grass, and carrion from such mammals as deer and rabbits (Gardner 1982).

Interesting notes: Owing to their unique marsupium, the birth of opossums is particularly fascinating. Female opossums can have up to two litters per year with sizes ranging from one to 17 newborns per litter. The young are born in an embryonic stage 12 or 13 days after conception and are only about one-half inch long and one-tenth of an inch wide. You could fit an entire litter into a teaspoon. After emerging from the uterus, the newborns have to climb one to two inches from their mother's vulva to the pouch where they attach themselves to one of 13 nipples. Not all newborns will reach a nipple and not all nipples will be functional if they arrive. Sometimes only seven to ten of the 13 nipples will produce milk. Those newborns that can't find a fucntional nipple perish. After attaching, the tiny opossums will stay attached and nurse for 50 to 65 days. They are weaned after 95 to 105 days (Gardner 1982; McManus 1974; Asdell 1964).

Opossums are probably best known for playing dead, a defense mechanism that is utilized to keep them from being eaten and is only used as a last resort. Opossums don't move very swiftly, their fastest speed was clocked at a roaring 4½ miles per hour (McManus 1970). Instead, they have developed another way to escape predators called "death feigning" (pretending to die). This unusual habit of defense is successful because predators don't often attack or eat dead animals and they don't always eat their prey as soon as they have captured it. "Playing possum" has also been observed in ducks, rodents, reptiles, and amphibians (McFarland 1982).

While pretending to be dead the opossum lies on its side, opens it mouth slightly, draws the corners of its mouth back, and begins to drool. The eyes remain open. If the predator goes away the opossum may recover immediately or it may take up to 20 minutes to start moving again. Even though they are "feigning death" and don't react to being probed, opossums "playing possum" are still aware of what is going on around them. In fact, experiments have shown that certain body measurements like heart rate and brain waves are no different between an awake opossum and one "feigning death" (Franq 1969). Opossums can feign death for a period of several minutes up to six hours (McManus 1970).

Opossums are not native to the west but were brought here from the eastern United States. It is difficult to trace the current population back to its roots, but they probably originated from several different planned and unplanned introductions. For example, between 1910 and 1930 eight opossums were introduced into Umatilla County, Oregon. Most of these were pets and either escaped or were released by their owners. This small number was apparently enough to start a local population, as opossums started showing up in traps set for minks and skunks several years later in that area. These were doubtless not the only occurrences of opossums being released, but it is one of the earliest recordings and most likely helped to establish the current population ranging throughout Oregon (Jewett and Dobyns 1929).