NEW WORLD OPOSSUMS – [Didelphimorphia]

PHYSICAL CHARACTERISTICS

The word “opossum,” commonly used to refer to all species

within the family Didelphidae, is derived from an Algonquian

Indian word for the Virginia opossum, the only living marsu-

pial species north of the U.S.-Mexico border. “Possum,” with-

out the first “O,” refers to certain Old World marsupials in

Australia and New Guinea.

Didelphidae are tiny to medium-sized animals, most tending

toward the smaller end of the size spectrum. Males are larger

than females. In most species, the tail is about the same length

as the combined head-and-body length, or longer, scaly and

only lightly furred, and is prehensile (able to grasp) to varying

degrees among species. In the smallest species, adult head and

body length runs 3.3 to 7.2 inches (8.5 to 18.5 centimeters)

and tail length is 3.5 to 10 inches (9 to 25 centimeters). In the

largest species, adult head and body length runs 13 to 19.5

inches (32.5 to 50 centimeters) and tail length is 10 to 21 inches

(25.5 to 53.5 centimeters). Adult weight in the larger

species is usually between 4.5 and 12 pounds (2 and 5.5

kilograms).

The limbs of Didelphidae are short, except for the yapok (or

water opossum), whose hind legs are a little longer than the

forelegs. All four feet bear five digits and the hallux (HAL-lux;

big toe) is opposable. All digits are clawed, except for some

species in which the hallux lacks a claw. The muzzle (mouth

area) is long and pointed, and the ears are prominent. The ca-

nine teeth are long and large.

The fur may be fine and velvety, thick and woolly, or some-

what coarse and stiff. Pelt colors, combinations, and patterns

vary widely among genera (JEN-uh-rah) and species. The brown

four-eyed opossum and the gray four-eyed opossum owe their

common names to a colored spot of fur above each eye. In some

species, there are dark brown or black patches around the eyes.

In most Didelphidae species, the back and sides of the body

are dark, the underparts lighter. Upperparts may be gray, dark

brown or reddish brown, the underparts white or yellowish. The

thick-tailed opossum has an elaborate coloration that varies

among individuals. The upper body fur may be yellow, yellow-

brown, or dark brown, while the underparts are reddish-brown,

light brown, or dark brown. The fur may have an unusual pur-

ple tinge. The face may show vague markings. The body shape

of this species is also unusual, tending toward a long, low-slung,

weasel-like form, with short but strong legs.

GEOGRAPHIC RANGE

In a very general sense, the Didelphidae can be said to in-

habit both New World continents, from southeastern Canada

to southern South America, but the common or Virginia opos-

sum is the only marsupial making its home in the continental

U.S. and Canada. All other species of Didelphidae range across

Mexico, Central, and South America, from northern Mexico to

southern Patagonia in South America, and on some of the Lesser

Antilles Islands.

HABITAT

The Virginia opossum inhabits the widest range of habitats of

any New World opossum, being found over most of the conti-

nental United States and southeastern Canada, in forest, grass-

land, and desert. The other species variously inhabit tropical and

subtropical forests, and a few, like the Patagonian opossum, in-

habit temperate grasslands in South America. The dryland mouse

opossum prefers desert-like conditions in Central America.

DIET

Diet among Didelphidae is omnivorous, with some variation

among species. Food sources include insects, small reptiles,

small mammals, especially rodents, birds’ eggs, fruits, seeds,

snails, freshwater crustaceans, earthworms, and carrion. One

species is skilled at subduing scorpions. The yapok, or water

opossum, hunts and eats freshwater fish. Some species store fat

in the bases of their tails to carry them through the lean months.

BEHAVIOR AND REPRODUCTION

New World opossums are marsupials, mammals that give birth

to tiny, only partly developed young that crawl into the mother’s

pouch, latch their jaws tightly onto a milk nipple, and finish their

development. Most mammals are placental, meaning that they

carry their young in the womb for longer periods before birthing

them, and these are born in a more completely developed state.

“Marsupial” comes from “marsupium,” the Latin word for pouch

or bag, and names that special feature of marsupials.

Not all species have females with complete, functional

pouches. In species without pouches, newborn young just cling

with their jaws onto the mother’s nipples and grasp her fur, re-

maining so until weaning, or stopping breastfeeding, and cling-

ing to the mother wherever she goes. Some of the non-pouched

opossums have partial pouches that cover only the rows of nip-

ples on either side, and run the length of the underbelly. Fe-

males may have from five to as many as twenty-five nipples. In

the common large opossum species, a typical female has a func-

tional, snug, fur-lined pouch and thirteen nipples inside,

arranged in a circle, with one nipple in the center, although the

number of nipples may vary among species and even among

individual females within a species.

American opossums may have definite mating seasons in

more temperate regions, or may breed anytime of the year in

the tropics. Litter sizes generally run between four and nine

young. As many as sixteen young, or a record fifty-two for the

Virginia opossum, may be born in a single litter. In such large

litters, some of the young are likely to die before weaning, de-

pending on the number of nipples the mother has. The gesta-

tion period is short, about two weeks, followed by up to ten

weeks of pouch life. When leaving the pouch, the young may

still nurse and ride on their mother’s back for another month

before striking off on their own. Individuals reach reproduc-

tive age at four months to one year. Lifespans among Didel-

phidae species are short, only one to five years.

For shelter, some American opossum species build nests of

twigs and leaves, or of grasses; others dig their own burrows

or use burrows abandoned by other animals, abandoned birds’

nests, or shelter in hollow logs and among rocks.

All but a few species are nocturnal (nighttime) foragers, and

as far as anyone knows, all are solitary, breaking that rule only

during mating times. Outside of the mating season, same-sex

individuals of a species, upon meeting, ignore or threaten each

other. During the breeding season, a male and female may stay

together for several days. Some species are mainly arboreal

(spending most of their time in trees), others forage on the

ground, and some do both. The Patagonian opossum is an ex-

cellent swimmer in freshwater, where it hunts for fish, even

though it is not as specialized as the water opossum.

NEW WORLD OPOSSUMS AND PEOPLE

As a whole, the Didelphidae are no threat or bother to hu-

mans. People hunt and eat some species and use their fur for

clothing and parts of clothing. The gray short-tailed opossum

frequents houses in South America, where it is welcome be-

cause it hunts and eats rodents and insects infesting the houses.

Brown four-eyed opossums, gray four-eyed opossums,

woolly opossums, and common mouse opossums occasionally

raid fruit and corn crops. The southern opossum, and the white-

eared opossum sometimes kill poultry.

CONSERVATION STATUS

Out of all the Didelphidae species, the IUCN lists three as

Critically Endangered (facing an extremely high risk of ex-

tinction), three as Endangered (facing a very high risk of ex-

tinction), fifteen as Vulnerable (facing a high risk of extinction),

and eighteen as Near Threatened (close to becoming threatened

with extinction).