Didelphis virginianaVirginia opossum

Last updated:

Geographic Range

Virginia opossums (Didelphis virginiana) have a wide range throughout Central and North American, which continues to expand. Currently, Virginia opossums can be found from Costa Rica to southern Ontario, Canada. This species is not ubiquitous throughout the United States, Virginia opossums are typically found east of the Rocky Mountains and along the west coast; they are restricted by temperature and snow depth. The movement of this Neotropical species northward has been the subject of research. In the 1970’s, a scientific model hypothesized that this species would not venture beyond Vermont and New Hampshire. Prior to European settlement, their range was limited in the north to Kentucky, Indiana and Ohio. Given their tropical beginnings, it is not surprising that Virginia opossums are ill-equipped for extreme cold, with inadequate thermoregulatory abilities and poorly insulated fur. Instead, the survival of Virginia opossums is likely facilitated by their behavioral modification during extreme temperatures and the shelter offered by human structures, although reports of frost bite are common for northern populations. (Cuaron, et al., 2012; Harmon, et al., 2005; Hossler, et al., 1994; Kanda, 2005)

Habitat

Virginia opossums may be found in a fairly wide range of habitats; however, they typically prefer areas near a water source, such as a stream or swamp. These animals may live in woodlands and thickets but they are very often found within human altered areas. This species has been extremely successful due to their ability to thrive in urban areas; this is assisted by their small body size, nocturnal habits and high reproductive output. Virginia opossums nest in brush piles, hallow trees and drainage areas. They can be found from near sea level to 3,000 meters in elevation. (Cuaron, et al., 2012; Hoffmeister, 2002; McManus, 1974; Wright, et al., 2012)

  • Range elevation
    0 to 3,000 m
    0.00 to ft

Physical Description

Virginia opossums are robust marsupials, with short legs and thick bodies. Their pelage is typically grayish, but it may range from a reddish, brownish or even blackish hue. Within their fur, this species has long white tipped guard hairs. Their coloration may vary based on the range of the population; for instance, northern populations tend to have lighter guard hairs, thicker under fur and a more grizzled appearance, whereas southern populations generally appear darker and have thinner under fur. Albinism has been reported in this species. The fur of their face tends to be lighter than the rest of their body; it is typically pale grayish-white. They have large delicate ears, which are predominately furless, making frost bite to that region extremely common. Likewise, their long tails are also common victims of frost bite. Although there is fur at the base of their tail, it is largely hairless throughout. Virginia opossums’ tails are very long, they tend to be about 93% as long as their head to body length. This species is terrestrial, but they are also adept climbers. They have prehensile tails that are used as an additional limb and are crucial for climbing. Their dark feet are also specialized for climbing, including an opposable hallux. Although there is some disagreement regarding sexual dimorphism, adult male Virginia opossums tend to be slightly larger than adult females. Males often weigh between 2.1 to 2.8 kg, whereas females generally range between 1.9 to 2.1 kg. These may be under-estimates, as some sources claim Virginia opossums’ body weight ranges from 3 to 6 kg. Weight measurement can range based on the animals chosen habitat; populations in urban areas tend to have a body mass that is approximately 34% larger than rural conspecifics. Body and tail length estimates also vary; males have an average body length of 40.8 cm, with a tail length of 29.4 cm, whereas female body lengths average 40.6 cm, with a tail length of 28.1 cm. However, other published estimates suggest body length may range from 33 to 55 cm, with a tail length of 25 to 54 cm. Virginia opossums have the following dental formula: 5/4, 1/1, 3/3, 4/4. (Burnie, et al., 2001; Christiansen, 2006; Gipson and Kamler, 2001; Hoffmeister, 2002; Hossler, et al., 1994; McManus, 1974; McRuer and Jones, 2009; Wright, et al., 2012)

  • Sexual Dimorphism
  • male larger
  • Range mass
    1.9 to 6 kg
    4.19 to 13.22 lb
  • Range length
    33 to 55 cm
    12.99 to 21.65 in
  • Average basal metabolic rate
    5.299 W
    AnAge

Reproduction

Didelphid marsupials engage in a polygynous mating system, in which males vie for reproductive females. Male Virginia opossums possess a sexually dimorphic scent gland on their chest, which emits a musky odor and stains their fur; this is most commonly observed near the onset of the breeding season. Females experience an approximately 29.5 day estrous cycle, upon entering estrous, breeding begins almost immediately. Mating behavior is one of the only social behaviors displayed by Virginia opossums, after mating; females resume their aggressive, solitary disposition. (Christiansen, 2006; Fernandes, et al., 2010; Holmes, 1992a; McManus, 1974)

Virginia opossums become sexually mature within the first year of their life, around 6 months for females and 8 months for males, but typically begin breeding around 10 months of age. This species has a long breeding season, however, the exact months of the breeding season varies based on an individual’s location. In populations found at 44° N latitude, the breeding season lasts from February to September, whereas at 30°N latitude, the breeding season typically lasts from January to August. Likewise, the number of litters per year varies based on the climate. In northern regions, Virginia opossums average only one litter per year, in warmer climates the number of litters may increase to 3 per year. After an extremely short gestation period of 12 to 13 days, 4 to 25 altricial “honey bee-sized” young are born, although females generally have only 13 mammae, some of which may be nonfunctional. The offspring weigh between 0.13 to 0.20 grams and are generally about 14 mm long. Although their newborn offspring are highly under-developed in many regards, the young do possess muscular front legs, allowing them to climb to the mothers pouch. Many young will not survive the trip to the pouch, those who do, remain attached to the mammae for approximately 50 to 70 days, females average about 8 pouch-young per litter. After the period spent within the pouch, the young remain with their mother, either staying in the den while she forages, or riding on her back. The young begin eating solid food at around 85 days old and are fully weaned between 93 to 105 days old. After this period, young are typically independent, although some will stay in the weaning den with their mother until they are about 120 days old. About 60% of the young will not survive once they are fully independent. (Burnie, et al., 2001; Christiansen, 2006; Feldhamer, et al., 2007; Hoffmeister, 2002; Holmes, 1992b; Hossler, et al., 1994; McManus, 1974; O'Connell, 2006; Rademaker and Cerqueira, 2006)

  • Breeding interval
    This species has 1 to 3 litters per year; this varies based on a populations range.
  • Breeding season
    The exact breeding season for this species varies based on a population’s range, in more northern climates they breed from February to September; in ranges further south they breed from January to August.
  • Range number of offspring
    4 to 25
  • Average number of offspring
    15
    AnAge
  • Range gestation period
    12 to 13 days
  • Range weaning age
    93 to 105 days
  • Range time to independence
    93 to 105 days
  • Average age at sexual or reproductive maturity (female)
    6 months
  • Average age at sexual or reproductive maturity (female)
    Sex: female
    184 days
    AnAge
  • Average age at sexual or reproductive maturity (male)
    8 months
  • Average age at sexual or reproductive maturity (male)
    Sex: male
    243 days
    AnAge

Virginia opossums invest little in parental care; males provide no parental care, while females offer moderate care. After breeding, the female’s pouch takes on a brownish-orange hue and emits a musky odor due to scent glands located within; this likely assists newborn opossums in finding their mothers pouch. While young are residing within, females are often observed licking at the pouch and their offspring. This practice led to the mistaken idea that Virginia opossums breed with their noses and afterward, the young crawl from the female’s nostrils into her pouch. Although a female with pouch-young may become very protective of her pouch, once her young are removed, females show little interest. Female Virginia opossums typically continue lactating for about 15 weeks, over which time, the composition of the milk becomes modified. Most young Virginia opossums become solitary after weaning, however, some may remain with their mother in their weaning den until they are about 120 days old. (Holmes, 1992b; Kimble, 1997; McManus, 1974; McRuer and Jones, 2009; Porter, 1956)

  • Parental Investment
  • female parental care
  • pre-weaning/fledging
    • provisioning
      • female
    • protecting
      • female
  • pre-independence
    • protecting
      • female

Lifespan/Longevity

Virginia opossums have a fairly short lifespan; wild individuals typically only survive about 1.5 to 2 years. Early in life, young opossums have a very high mortality rate. Many of these altricial young never arrive in their mothers pouch, afterward; about 60% of those who do reach the pouch will perish once they are weaned. Among adult animals, the vast majority of deaths occurred during the cold season. Although males typically only participate in breeding for one year, they are technically not semelparous because most ranges involve 2 to 3 breeding seasons per year. However, in one study, among approximately 12,000 trapped Virginia opossums, no adult males were found. Females may live slightly longer than their male counterparts; however, they are no longer reproductively viable after 2 years of age. Captive individuals typically have a longer lifespan; they generally survive to be 3 to 4 years old; however, there are reports of captive Virginia opossums surviving until they are 8 to 10 years old. (Christiansen, 2006; Gipson and Kamler, 2001; Harmon, et al., 2005; Hossler, et al., 1994; McManus, 1974; McRuer and Jones, 2009; O'Connell, 2006; Woods II and Hellgren, 2003)

  • Range lifespan
    Status: captivity
    10 (high) years
  • Typical lifespan
    Status: wild
    1.5 to 2 years
  • Typical lifespan
    Status: captivity
    3 to 4 years
  • Range lifespan
    Status: wild
    2.5 (high) years
    AnAge

Behavior

Virginia opossums are solitary, nocturnal and terrestrial; however, they are also very adept climbers and may den in trees. This species begins its nightly activities around dusk and remains active until dawn; this may vary slightly throughout the year. These animals do not hibernate; however, they reduce their activity during the bitter cold seasons. During their active period, males travel greater distances, whereas females shows greater variation in their movement. This neotropically evolved species is able to survive into Canada primarily through behavioral modification and metabolism of fat stores. This species copes with extreme heat by spreading their saliva as a cooling mechanism. Their northward migration is partially facilitated by their ability to flourish in human altered environments. Denning sites vary; this species may use buildings, hallow trees or abandoned burrows. They fill their den with substrate including dry leaves or shredded paper. Virginia opossums change denning sites often; they remain in the same den for long periods only while they are weaning young. Aggressive encounters between males may involve a ‘dance’ in which they lash their tails and reach with their front legs. However, captive individuals raised together may form non-aggressive hierarchies in which females are dominant. Virginia opossums are famous for entering a defensive catatonic state, commonly known as “going opossum”. During this death feigning behavior the animal becomes motionless, this behavior may last as little as a minute, or it may continue up to 6 hours. This behavior is relatively rare and is most frequently displayed in young opossums. Instead, it is more common for a threatened adult to bare their teeth and stand their ground, or flee. Virginia opossums have a reputation for being extremely slow and clumsy; however, they are known to show directional turns when pursued to avoid being captured and their quadrupedal plantigrade stance allows them to run 7.1 to 7.4 km per hour. Likewise, Virginia opossums may also climb or swim to escape a perceived threat. (Allen, et al., 1985; Cuaron, et al., 2012; Hoffmeister, 2002; Hossler, et al., 1994; Kimble, 1997; Ladine and Kissell Jr, 1994; McManus, 1974; McRuer and Jones, 2009)

Home Range

The home range kept by Virginia opossums varies greatly. This may depend on their range, their habitat, the availability of resources and their gender. In general, their home range size is thought to be about 12.5 to 38.8 hectares; females generally have a smaller home range. A study conducted in Georgia found that home range size may be between 7.2 to 94.4 hectares, a study in Texas found home range sizes from 0.12 to 23.47 hectares; likewise, home range sizes in urban environments averaged 18.8 hectares for females and 37.3 hectares for males. Males are believed to keep larger home ranges because their reproductive success is based solely on their ability to find mates, whereas female success is based on the accessibility of food items. Their home ranges are oval shaped and often overlap with a water source. Virginia opossums were once considered a nomadic species but more recent research has shown that an individual maintains a fairly constant home range throughout their lifespan. (Allen, et al., 1985; Gehrt, et al., 1997; Gipson and Kamler, 2001; Harmon, et al., 2005; McManus, 1974; O'Connell, 2006; Wright, et al., 2012)

Communication and Perception

Virginia opossums use olfactory and auditory signals to communicate with their young, mates and potential aggressors. Scent glands help neonates locate their mothers pouch. Male’s sexually dimorphic sternal scent glands emit a musky odor and stain their fur, primarily just before mating season begins. Males are able to detect females based on scent, research suggests that males are able to identify particular females based on scent alone, whereas females are able to distinguish between the genders but are not able to discern among individual males. During aggressive encounters, Virginia opossums may produce an excretion from their anal glands. In addition, females maintain auditory contact with their young through a series of clicks, lip smacking and bird-like sounds. When threatened, these animals may hiss, growl or screech. During the breeding season, mates may communicate with a series of metallic sounding clicks. Virginia opossums likely have acute hearing. Their perception channels are specialized for their nocturnal behavior. They have sensitive vibrissae, which assist in their movement in the dark. Their vision is likely similar to cats, however, they have a rod to cone ratio of 50:1, as opposed to a cat’s ratio of 10:1. While they likely have keen eyesight, their ability to recognize color is limited. Their ability to recognize specific tastes is likely also limited. (Christiansen, 2006; Holmes, 1992a; Kimble, 1997; Kolb and Wang, 1985; McManus, 1974; O'Connell, 2006)

Food Habits

Virginia opossums are extremely opportunistic feeders. These animals eat a variety of foods based on the season, their habitat and their range. Their diets include vertebrates, invertebrates, plant material, fruits, grains and carrion. During the colder seasons, small vertebrates tend to make up a larger portion of their diet, whereas in the warmer seasons, they consume more invertebrates, plant material, fruits and seeds. Stomach content analyses have been conducted on Virginia opossums throughout the United States, generally their diet is composed of 14 to 27% mammal tissues, 10 to 18% fruits, seeds and bulbs, 6 to 11% grasses and leaves, 3 to 13.5% insects, 5.5 to 9% earthworms and 3 to 5% birds. Other food items were found more specific to an animal’s location and included up to 22.5% reptiles and amphibians, 10% gastropods, 9% pet food, 9% garbage and up to 5% carrion. (Christiansen, 2006; Hopkins and Forbes, 1980; McManus, 1974; McRuer and Jones, 2009)

  • Animal Foods
  • birds
  • mammals
  • amphibians
  • reptiles
  • carrion
  • insects
  • terrestrial worms
  • Plant Foods
  • leaves
  • seeds, grains, and nuts
  • fruit

Predation

Virginia opossums may be predated upon by a variety of species including owls, domestic dogs, coyotes, red foxes, raccoons, bobcats and large snakes, among others. They may also be hunted or trapped by humans. Virginia opossums are immune to the venom of a variety of snakes from Family Viperidae including eastern and western diamondback rattlesnakes, copperheads, cottonmouth moccasins and Korean mamusi. This species may have a better chance of survival within more urban environments due partially to the lower predation risk. (Harmon, et al., 2005; Hossler, et al., 1994; Ladine and Kissell Jr, 1994; Werner and Vick, 1977)

Ecosystem Roles

Virginia opossums are opportunistic omnivorous feeders. They consume a variety of vertebrates, invertebrates, plant material and carrion. Virginia opossums are important seed dispersers and redistribute undamaged seeds from the genera Asimina and Diospyros, among others. These animals are also carriers for a wide variety of internal and external parasites. Virginia opossums are known carriers of at least 24 internal and 13 external parasites. Although they are not immune, it is unusual for this species to be a carrier of the rabies virus. (Baker, et al., 1995; Durden and Nixon, 1990; McManus, 1974; McRuer and Jones, 2009; Monet-Mendoza, et al., 2005; Rejmanek, et al., 2009; Willson, 1993)

  • Ecosystem Impact
  • disperses seeds
Commensal/Parasitic Species

Economic Importance for Humans: Positive

Given the frequent urban habitation of Virginia opossums, interaction with humans is almost inevitable. These animals are hunted for sport and food. Some cultures believe that Virginia opossums’ meat has medical properties. For instance, eating their meat in a soup is believed to help inflammation, colitis, gastritis and skin infections. Likewise eating cooked Virginia opossum meat is believed to prevent heart attacks, using an ointment composed of opossum fat is believed to treat epilepsy and infusing opossum bones in water is believe to treat allergies, dermatitis and coughing. Virginia opossums’ pelts may also be sold commercially. Although it is illegal in many states, Virginia opossums are sometimes kept as pets. In such situations, these animals may be successfully litter trained and adapt to the diurnal lifestyle of their owners. Obesity is common among captive Virginia opossums. (Alonso-Castro, et al., 2011; Cuaron, et al., 2012; Jacobo-Salcedo, et al., 2011; McManus, 1974; McRuer and Jones, 2009)

Economic Importance for Humans: Negative

Virginia opossums are often seen a pest species. Stomach content analyses in Portland, Oregon found that as much as 9% of an opossums diet was composed of garbage, likewise, another 9% of their diet was pet food. Virginia opossums are also seen as farm pests due to their proclivity for poultry. (Cuaron, et al., 2012; McRuer and Jones, 2009)

Conservation Status

Virginia opossums are currently listed as a species of least concern according to the IUCN Red List of Threatened Species. This animal’s ability to adapt to human altered habitats has made it extremely successful and widespread. Virginia opossums do not merely tolerate human settlements; they flourish and have a greater survival rate near them. (Cuaron, et al., 2012; Harmon, et al., 2005; Wright, et al., 2012)

Contributors

Leila Siciliano Martina (author), Animal Diversity Web Staff.

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

Neotropical

living in the southern part of the New World. In other words, Central and South America.

World Map

acoustic

uses sound to communicate

agricultural

living in landscapes dominated by human agriculture.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carrion

flesh of dead animals.

causes or carries domestic animal disease

either directly causes, or indirectly transmits, a disease to a domestic animal

chemical

uses smells or other chemicals to communicate

drug

a substance used for the diagnosis, cure, mitigation, treatment, or prevention of disease

endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

female parental care

parental care is carried out by females

food

A substance that provides both nutrients and energy to a living thing.

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

introduced

referring to animal species that have been transported to and established populations in regions outside of their natural range, usually through human action.

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

nocturnal

active during the night

omnivore

an animal that mainly eats all kinds of things, including plants and animals

polygynous

having more than one female as a mate at one time

scrub forest

scrub forests develop in areas that experience dry seasons.

seasonal breeding

breeding is confined to a particular season

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

solitary

lives alone

suburban

living in residential areas on the outskirts of large cities or towns.

swamp

a wetland area that may be permanently or intermittently covered in water, often dominated by woody vegetation.

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

terrestrial

Living on the ground.

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

urban

living in cities and large towns, landscapes dominated by human structures and activity.

visual

uses sight to communicate

viviparous

reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.

References

Allen, C., R. Marchinton, W. MacLentz. 1985. Movement, habitat use and denning of opossums in the Georgia piedmont. American Midland Naturalist, 113:2: 408-412.

Alonso-Castro, A., C. Carranza-Alvarez, J. Maldonado-Miranda, M. Jacobo-Salcedo, D. Quezada-Rivera, H. Lorenzo-Marquez, L. Figueroa-Zuniga, C. Fernandez-Galicia, N. Rios-Reyes, M. de Leon-Rubio, V. Rodriguez-Gallegoes, P. Medellin-Milan. 2011. Zootherapeutic practices in Aquismon, San Luis Potos, Mexico. Journal of Ethnopharmacology, 138: 233-237.

Baker, D., L. Cook, E. Johnson, N. Lamberski. 1995. Prevalence acquistition, and treatment of Didelphostrongylus hayesi (Nematoda: Megastrongyloidea) infection in opossums (Didelphis virginiana). Journal of Zoo and Wildlife Medicine, 26:3: 403-408.

Burnie, D., D. Wilson, J. Clutton-Brock. 2001. Animal. New York: DK Publishing Inc.

Christiansen, P. 2006. The Encyclopedia of Animals. London: International Masters Publishers.

Cuaron, A., L. Emmons, K. Helgen, F. Reid, D. Lew, B. Patterson, C. Delgado, S. Solari. 2012. "Didelphis virginiana" (On-line). IUCN Red List of Threatened Species. Accessed May 02, 2013 at www.iucnredlist.org.

Durden, L., W. Nixon. 1990. Ectoparasitic and phoretic arthropods of Virginia opossums (Didelphis virginiana) in central Tennessee. Journal of Parasitology, 76:4: 581-583.

Feldhamer, G., L. Drickamer, S. Vessey, J. Merritt, C. Krajewski. 2007. Mammalogy: Adaptation, Diversity, Ecology. Baltimore: The John Hopkins Press.

Fernandes, F., L. Cruz, E. Martins. 2010. Growth and home range size of the gracile mouse opossum Gracilinanus microtarsus (Marsupialia: Didelphidae) in Brazilian cerrado. Journal of Tropical Ecology, 26:2: 185-192.

Gehrt, S., D. Clark, E. Fritzell. 1997. Population dynamics and ecology of Virginia opossums in southern Texas. The Southwestern Naturalist, 42:2: 170-176.

Gipson, P., J. Kamler. 2001. Survival and home ranges of opossums in northeastern Kansas. The Southwestern Naturalist, 46:2: 178-182.

Harmon, L., K. Bauman, M. McCloud, J. Parks, S. Howell, J. Losos. 2005. What free-ranging animals do at the zoo: A study of the behavior and habitat use of opossums (Didelphis virginiana) on the grounds of the St. Louis Zoo. Zoo Biology, 24: 197-213.

Hoffmeister, D. 2002. Mammals of Illinois. Urbana: University of Illinois Press.

Holmes, D. 1992. Odor as cues for orientation to mothers by weaning Virginia opossums. Journal of Chemical Ecology, 18:12: 2251-2259.

Holmes, D. 1992. Sternal odors as cues for social discrimination by female Virginia opossums, Didelphis virginiana. Journal of Mammalogy, 73:2: 286-291.

Hopkins, D., R. Forbes. 1980. Dietary patterns of the Virginia opossum in an urban environment. The Murrelet, 61:1: 20-30.

Hossler, R., J. McAninch, J. Harder. 1994. Maternal denning behavior and survival of juveniles in opossums in southeastern New York. Journal of Mammalogy, 75:1: 60-70.

Jacobo-Salcedo, M., A. Alonso-Castro, A. Zarate-Martinez. 2011. Folk medicinal use of fauna in Mapimi, Durango, Mexico. Journal of Ethnopharmacology, 133: 902-906.

Kanda, L. 2005. Winter energetics of Virginia opossums Didelphis virginiana and implications for the species' northern distributional limit. Ecography, 28:6: 731-744.

Kimble, D. 1997. Didelphid behavior. Neuroscience and Biobehavioral Reviews, 21:3: 361-369.

Kolb, H., H. Wang. 1985. The distribution of photoreceptors, Dopaminergic Amacrine cells and ganglion cells in the retina of the North American opossum (Didelphis virginiana). Vision Research, 25:9: 1207-1221.

Ladine, T., R. Kissell Jr. 1994. Escape behavior of Virginia opossums. American Midland Naturalist, 132:2: 234-238.

McManus, J. 1974. Didelphis virginiana. Mammalian Species, 40: 1-6.

McRuer, D., K. Jones. 2009. Behavioral and nutritional aspects of the Virginia opossum (Didelphis virginiana). Veterinary Clinics of North America: Exotic Animal Practice, 12:2: 217-236.

Monet-Mendoza, A., D. Osorio-Sarabia, L. Garcia-Prieto. 2005. Helminthes of the Virginia opossum (Didelphis virginiana) (Mammalia: Didelphidae) in Mexico. Journal of Parasitology, 91:1: 213-219.

O'Connell, M. 2006. American Opossums. Pp. 808-813 in D MacDonald, S Norris, eds. The Encyclopedia of Mammals, Vol. 1. London: The Brown Reference Group.

Porter, K. 1956. The 'possum in Midwestern folklore. Western Folklore, 15:1: 23-25.

Rademaker, V., R. Cerqueira. 2006. Variation in the latitudinal reproductive patterns of the genus Didelphis (Didelphimorphia: Didelphidae). Austral Ecology, 31:3: 337-342.

Rejmanek, D., E. Vanwormer, M. Miller, J. Mazet, A. Nichelason, A. Melli, A. Packham, D. Jessup, P. Conrad. 2009. Prevalence and risk factors associated with Sarcocystis neurona infections in opossums (Didelphis virginiana) from central California. Veterinary Parasitology, 166: 8-14.

Werner, R., J. Vick. 1977. Resistance of the opossum (Didelphis virginiana) to envenomation by snakes of the family Crotalidae. Toxicon, 15:1: 29-32.

Willson, M. 1993. Mammals as seed-dispersal mutalists in North America. Oikos, 67:1: 159-176.

Woods II, H., E. Hellgren. 2003. Seasonal changes in the physiology of male Virginia opossums (Didelphis virginiana): Sign of the dasyurid semelparity syndrome. Physiological and Biochemical Zoology, 76:3: 406-417.

Wright, J., M. Burt, V. Jackson. 2012. Influences of an urban environment on home range and body mass of Virginia opossums (Didelphis virginiana). Northeastern Naturalist, 19:1: 77-86.