General: The opossum (Didelphia virginiana) is one of the oldest known mammals, having been traced back 70 million years through fossilized remains. Over 60 species of this common mammal are now found across North and Central America. The opossum is the only marsupial found in North America1 and is notable for the unique presence of a pouch that is used to protect, nourish and raise young. You may come across one of these nocturnal animals wondering quietly at night or even hanging from their prehensile tails from a tree branch. Unfortunately, many opossums are killed by automobiles because of their tendency to eat carrion. Despite their high mortality rates, opossums are widespread with healthy populations and are listed as least concern on the IUCN Red List.
Description: Opossums are slow, clumsy heavyset mammals that reach a mature weight of 8.8 to 13.2lbs. and nose-to-tail length of up to 30”, with males being slightly larger than females. They have easily identifiable elongated heads with conical snouts and long whiskers. The skull of the opossum contains 50 teeth, more than most other mammals within their habitats (a feature that is indicative of the opossum’s ancient lineage2.) Opossums are possibly best known for their long, tapered prehensile tails that are scaly in appearance. This type of tail is used as a fifth limb and is adapted for gripping and wrapping, aiding in climbing and allowing opossums to hang from their tails for short periods of time. Opossums also have hand-shaped feet with sharp claws that aid in climbing and an opposable hallux located on the interior of each rear foot. A hallux functions similar to a thumb and aids in gripping3. Opossums use these digits to groom their fur, faces, and front feet4. As members of the Didelphidae family (and the only marsupials found in North America,) female opossums have wooly, fur-lined pouches on their abdomens that are used to carry their young.
The coloration of opossums varies by region, but opossums generally appear gray with small black eyes set into a lighter or white face, black feet with white or pink toes, and leathery black ears with white or pink tips. Their coloration is a result of a dense white undercoat that is tipped in gray (or sometimes brown) with dark or black guard hairs. Southern populations tend to have a sparser undercoat. Albino mutations are not uncommon and result in a white coat, ears and feet and pink eyes5.
Opossums are nocturnal and use their senses of smell to locate food. While their level of intelligence is undetermined, opossums are known to have poor and limited social interactions. Males tend to be solitary and aggressive when in close proximity to other males. Females often live in groups. Opossums exhibit a number of behaviors when threatened (both aggressive and passive,) including growling, urinating, defecating and belching. Outside of growling and audible aggressive displays, opossums are relatively quiet. Most notably, opossums may play dead or “play ‘possum” when threatened. This includes rolling over and lying stiff with closed or fixed eyes, drooling, sticking out their tongues, and slowing their breathing until almost undetectable. This behavior may last for hours until the threat has passed. Opossums may run from threats and have also been known to swim to escape danger.
Opossums do not hibernate but will retreat into dens during extreme temperatures to avoid the risk of frostbite on their hairless extremeties6.
Habitat: Opossums are skilled climbers and nest and spend much of their time in trees in habitats including deciduous forests, farmlands, and open forests. They may be found in arid environments, but prefer moist habitats, including marshes, streams, and swamps.
Opossums do not establish territories (except for when females tend to remain in a small range when raising young7.) Instead, opossums tend to constantly move in unusual patterns in search of food.
Within their habitats, opossums fall prey to many predators, such as birds of prey, foxes, coyotes, and humans, who often hit opossums with cars. The young are susceptible to predators such as snakes and birds of prey8.
Location: Opossums may be found across North and Central America, including parts of the United States east of the Rockies as well as along the west coast. Opossums were introduced to California in 1890 and proceeded to spread along the west coast9. Their range continues to spread northward and populations can now be found in southwestern Ontario and British Columbia, Canada.
Diet: Opossums are omnivorous scavengers whose diets range from human garbage and carrion, to grass, fruit, nuts, berries, insects, snails, mice, birds, worms, and pet food. Their developed senses of smell allow them to locate sources of food at night, when they are most active.
Reproduction: Female opossums may have up to 3 litters in a year, depending on geographic location, at anytime from early spring through summer. Females nest in trees or dens built by other animals. The young are born approximately two weeks after mating occurs and the last litter of the year may still be traveling with the mother when the first litter of the next year is born10. Males offer no parental care or support beyond fertilization. Females may give birth to up to twenty young, born helpless and the size of jellybeans, but litters typically contain 5 to 8 babies. Immediately after birth, the young crawl into the mother’s pouch in search of one of her thirteen teats. Some young do not survive the trip to the pouch and only those that make it to the pouch and find a teat have a chance at long-term survival. The young develop within the pouch attached to the teats for approximately a month, at which point they begin leaving the pouch for periods of time to travel along with their mother, sometimes atop her back or clinging to her tail. The young may remain with their mother for as long as three months11.
Few opossums live past 18 months old because of high mortality rates (many deaths due to car accidents.) The oldest opossum captured was determined to be 3 years old12.
Notes of Interest: Opossums are one of the oldest mammals on Earth. Fossilized remains have determined that opossums existed during the age of the dinosaurs, approximately 70 million years ago13.
Opossums are hunted as furbearers as well as food.
Opossums earned their westernized name in 1608 when first spotted by Captain John Smith, derived from the Algonquin word for ‘white animal,’ apasum14.
Footnotes
1. http://animals.nationalgeographic.com/animals/mammals/opossum/
2. http://www.in.gov/dnr/fishwild/3367.htm
3. http://www.nhptv.org/natureworks/opossum.htm
4. http://animaldiversity.ummz.umich.edu/accounts/Didelphis_virginiana/
5. http://www.in.gov/dnr/fishwild/3367.htm
6. http://www.nhptv.org/natureworks/opossum.htm
7. http://www.opossum.org/
8. http://animaldiversity.ummz.umich.edu/accounts/Didelphis_virginiana/
9. http://animaldiversity.ummz.umich.edu/accounts/Didelphis_virginiana/
10. http://www.in.gov/dnr/fishwild/3367.htm
11. http://www.in.gov/dnr/fishwild/3367.htm
12. http://animaldiversity.ummz.umich.edu/accounts/Didelphis_virginiana/
13. http://www.opossum.org/
14. http://www.nhptv.org/natureworks/opossum.htm
http://animals.nationalgeographic.com/animals/mammals/opossum/
http://www.opossum.org/
http://www.nhptv.org/natureworks/opossum.htm
http://www.in.gov/dnr/fishwild/3367.htm
http://animaldiversity.ummz.umich.edu/accounts/Didelphis_virginiana/