"Simia vulpina", or "Monkey Fox", was the first scientific name of the common opossum of North America. It was applied by Konrad Gessner in his book Historiae Animalium in 1558. Gessner's name for the opossum probably says as much about the state of 16th century science as it does about the appearance of the animal. The modern, 20th century scientific name, "Didelphis marsupialis", encompasses four centuries of scientific and nomenclatural progress. "Didelphis" is Greek for "Double Womb" while "Marsupialis" is Latin for "of the Pouch". So the antiquated "Monkey Fox" has been replaced by "Double Womb of the Pouch". Perhaps we should switch to the Santee Sioux name for this animal which translates literally as "Big Rat'.

By whatever name, the animal in question has been known to Europeans since the early 1500's, when a female carrying young in her pouch was presented to the King and Queen of Spain by the explorer Pinzon. Amazed at this strange inhabitant of the New World, Ferdinand and Isabelle poked their royal fingers into the animal's pouch to verify that such a peculiar construction could indeed exist in nature.

Even today, we remain amazed that the female of this species possesses an external pouch in which her infants reside for an extended period after birth. Much of the folklore surrounding opossums centers around the presence of the pouch in the female, although other anatomical and behavioral peculiarities have given rise to their share of stories as well.

For example, people have believed and continue to believe that female opossums copulate through their noses and, at the appropriate moment, sneeze the newborn young into their pouches. The basis for this belief is undoubtedly the anatomy of the male reproductive organ, which is forked, and the rarity with which actual matings and births of this nocturnal animal are witnessed. In reality, the male organ corresponds to the branched reproductive tract and bifurcate uterus of the female and insures fertilization of the dozen or so eggs lying above each branch of the uterus. Being unfamiliar with the interior anatomy of the female and searching for a suitable receptacle for the unique male appendage has lead many a novice anatomist to the aforementioned erroneous conclusion.

Baby opossums are born 13 days after conception - the shortest gestation period for any North American mammal. At birth, the young have the size, shape, and appearance of embryos, yet crawl across the mother's fur and into her pouch where they will nurse more or less continuously for the next two months. The mother's pouch protects the young and keeps them warm during this period. Average litter size is 8 or 9 young.

Other hotbeds of opossum folklore concern its habit of playing dead and the use of its prehensile tail. Opossums do play dead. When faced with danger, opossums sometimes run away, sometimes bare their teeth and hiss, and sometimes fall into a catatonic state in which they appear to be dead. Other animals exhibit similar behavior, and "playing opossum" has been observed among birds, reptiles, amphibians, and some arthropods. This behavior has been associated most closely with opossums because they are relatively large, relatively common, and because they are so good at it.

Opossums play dead for periods of several minutes to several hours at a time. While playing dead they do not respond if they are poked, their whiskers are pulled, or even if their eyes are touched. Apparently playing dead is an involuntary response which confers some survival value on the participant. Animals accustomed to killing their prey may refrain from dining on a strange creature that dies before they can kill it.

Opossums can hang briefly from branches by their tails, at least when they are young. In reality, however, they rarely or never exhibit this behavior. Opossums do wrap their tails around twigs to steady themselves while climbing, but have no reason to hang by their tails while eating fruit, a position in which they are often erroneously depicted, since many other positions are steadier and much more comfortable. Obviously, opossums would never sleep while hanging by their tails.

Opossums sleep in a variety of locations, the males often denning up wherever they happen to be when the sun comes up. Females are somewhat more selective and in winter both sexes maintain home bases for longer durations, but apparently the concept of a home range is foreign to the fox monkey. Preferred denning sites, somewhat in order of preference, are: hollow trees, rock crevices, groundhog holes, beneath old sheds or outbuildings, abandoned squirrel nests, vine and shrub tangles, or under fallen logs.

In denning, especially during winter, opossums line their nests with leaves and other suitable debris, frequently carrying this nesting material by use of their tail. Possums do not hibernate, but may remain in their dens for days at a time, seldom venturing out if the temperature is below about 20 degrees Fahrenheit.

Opossums spend the majority of their waking hours wandering in an apparently random search pattern, presumably looking for food. They eat various animals and vegetables, living or dead, which they encounter during their travels. The bulk of their nonvegetable diet consists of insects and carrion. Their fondness for the latter menu item contributes to the relatively high roadkill rate for which this species is known.

The mental abilities of the monkey fox are generally held in low esteem. In part, this is due to the foraging and denning habits of the animal, which seem to be only a step above total randomness. In part, this is due to the physical appearance of the animal, particularly the protruding eyes and expressionless face. The almost total lack of vocalization and general lethargy of captive animals contribute to this unflattering reputation. The fact that a major defensive strategy of the animal is to "play dead" does not help.

The average wild opossum is a very young animal. Individuals more than two years old are uncommon in nature. In the northern part of their range, possums which have lived through at least one winter usually exhibit frost injury to their unprotected ears or tails. Opossums are also one of the most heavily parasitized of all North American animals, frequently serving as hosts to mites, fleas, roundworms, flukes, tapeworms, ticks, chiggers, trematodes, coccidians, nematodes and other internal and external parasites.

Why, then, are opossums so common? They are apparently ill equipped mentally, physically, and behaviorally to compete with other mammalian inhabitants of eastern North America. Yet during the past several centuries the monkey fox has extended its range hundreds of miles to the north. While stronger, swifter, and smarter species have become progressively restricted in numbers and range, opossums have proliferated. These slow and silent nomads of the night are one of the mammalian success stories of the century.

Various factors contribute to the success of the opossum. Because of their size, behavior, and nocturnal habits, there has been little human-possum interaction (human-animal interaction usually has a negative effect on wild animal population levels). Opossums are rarely hunted for meat or sport, and are seldom trapped for their fur, which is considered of inferior value (except to the opossums, of course).

Opossums do one thing extremely well, however, and that is to produce more possums. Moreover, the life history of the opossum emphasizes wandering as well as reproduction, a combination which insures both the loss of many individuals and the spread of the species into any suitable habitat. Baby opossums are produced in large quantities and at relatively low cost to the mother in terms of effort, training, and even gestation. Like a dandelion releasing its seeds into the wind, her offspring are sent off to wander through an uncaring world, yet possums and dandelions both turn up in large numbers and bloom in unexpected places.