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 1970ās, 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.
- Biogeographic Regions
- nearctic
- neotropical
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.
- Habitat Regions
- temperate
- tropical
- terrestrial
- Terrestrial Biomes
- forest
- scrub forest
- Wetlands
- swamp
- Other Habitat Features
- urban
- suburban
- agricultural
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
opossumsā 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 opossumsā 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.
- Other Physical Features
- endothermic
- bilateral symmetry
- Sexual Dimorphism
- male larger
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.
- Mating System
- polygynous
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 individualās 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 āhoney bee-sizedā 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.
- Key Reproductive Features
- seasonal breeding
- gonochoric/gonochoristic/dioecious (sexes separate)
- sexual
- viviparous
Virginia opossums invest little in parental care; males provide no parental care,
while females offer moderate care. After breeding, the femaleās 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 femaleās 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.
- Parental Investment
- female parental care
-
pre-weaning/fledging
-
provisioning
- female
-
protecting
- female
-
provisioning
-
pre-independence
-
protecting
- female
-
protecting
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.
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 ādanceā 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 āgoing opossumā. 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.
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.
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.
Maleās 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 catās 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.
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 animalās location
and included up to 22.5%
reptiles
and
amphibians
, 10%
gastropods
, 9% pet food, 9% garbage and up to 5% carrion.
- Primary Diet
- omnivore
- 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.
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.
- Ecosystem Impact
- disperses seeds
- Brachylaima virginiana (class Trematoda ; phylum Platyhelminthes )
- Paragonimus mexicanus (class Trematoda ; phylum Platyhelminthes )
- Rhopalias coronatus (class Trematoda ; phylum Platyhelminthes )
- Rhopalia macracanthus (class Trematoda ; phylum Platyhelminthes )
- Duboisiella proloba (class Trematoda ; phylum Platyhelminthes )
- Echinostomia revolutum (class Trematoda ; phylum Platyhelminthes )
- Mathevotaenia (class Cestoda ; phylum Platyhelminthes )
- Sarcocystis neurona (class Conoidasida ; phylum Apicomplexia )
- Oligacanthorhynchus tortuosa (class Archiacanthocephala ; phylum Acanthocephala )
- Oncicola luehei (class Archiacanthocephala ; phylum Acanthocephala )
- Pachysentis gethi (class Archiacanthocephala ; phylum Acanthocephala )
- Porrorchis nickoli (class Palaeacanthocephala ; phylum Acanthocephala )
- Didelphostrongylus hayesi (class Secernentea ; phylum Nematoda )
- Cruzia americana (class Secernentea ; phylum Nematoda )
- Cruzia tentaculata (class Secernentea ; phylum Nematoda )
- Gnathostoma procyonis (class Secernentea ; phylum Nematoda )
- Gnathostoma turgidum (class Secernentea ; phylum Nematoda )
- Gongylonema mexicanum (class Secernentea ; phylum Nematoda )
- Turgida turgida (class Secernentea ; phylum Nematoda )
- Didelphonema longispiculata (class Secernentea ; phylum Nematoda )
- Physaloptera turgid (class Secernentea ; phylum Nematoda )
- Trichuris didelphis (class Adenophorea ; phylum Nematoda )
- Viannaia didelphis (class Chromadorea ; phylum Nematoda )
- Viannaia viannai (class Chromadorea ; phylum Nematoda )
- Ctenocephalides felis (class Insecta ; phylum Arthropoda )
- Ctenophthalmus pseudagyrtes (class Insecta ; phylum Arthropoda )
- Cediopsylla simplex (class Insecta ; phylum Arthropoda )
- Orchopeas howardi (class Insecta ; phylum Arthropoda )
- Amblyomma americanum (class Arachnida ; phylum Arthropoda )
- Dermacentor variabilis (class Arachnida ; phylum Arthropoda )
- Archemyobia inexpectatus (class Arachnida ; phylum Arthropoda )
- Eutrombicula splendens (class Arachnida ; phylum Arthropoda )
- Leptotrombidium peromysci (class Arachnida ; phylum Arthropoda )
- Neotrombicula cavicola (class Arachnida ; phylum Arthropoda )
- Marsupialichus brasiliensis (class Arachnida ; phylum Arthropoda )
- Ornithonyssus wenecki (class Arachnida ; phylum Arthropoda )
- Didelphilichus serrifer (class Arachnida ; phylum Arthropoda )
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 opossumsā 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
opossumsā 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.
- Positive Impacts
- food
- body parts are source of valuable material
- source of medicine or drug
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.
- Negative Impacts
-
injures humans
- carries human disease
- crop pest
- causes or carries domestic animal disease
- household pest
Conservation Status
Virginia opossums are currently listed as a species of least concern according to
the IUCN Red List of Threatened Species. This animalās 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.
Additional Links
Contributors
Leila Siciliano Martina (author), Texas State University.
- 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.
- introduced
-
referring to animal species that have been transported to and established populations in regions outside of their natural range, usually through human action.
- native range
-
the area in which the animal is naturally found, the region in which it is endemic.
- Neotropical
-
living in the southern part of the New World. In other words, Central and South America.
- native range
-
the area in which the animal is naturally found, the region in which it is endemic.
- 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).
- tropical
-
the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.
- terrestrial
-
Living on the ground.
- forest
-
forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.
- scrub forest
-
scrub forests develop in areas that experience dry seasons.
- swamp
-
a wetland area that may be permanently or intermittently covered in water, often dominated by woody vegetation.
- urban
-
living in cities and large towns, landscapes dominated by human structures and activity.
- suburban
-
living in residential areas on the outskirts of large cities or towns.
- agricultural
-
living in landscapes dominated by human agriculture.
- polygynous
-
having more than one female as a mate at one time
- 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
- viviparous
-
reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.
- female parental care
-
parental care is carried out by females
- nocturnal
-
active during the night
- motile
-
having the capacity to move from one place to another.
- solitary
-
lives alone
- acoustic
-
uses sound to communicate
- chemical
-
uses smells or other chemicals to communicate
- visual
-
uses sight to communicate
- tactile
-
uses touch to communicate
- acoustic
-
uses sound to communicate
- chemical
-
uses smells or other chemicals to communicate
- carrion
-
flesh of dead animals.
- food
-
A substance that provides both nutrients and energy to a living thing.
- drug
-
a substance used for the diagnosis, cure, mitigation, treatment, or prevention of disease
- causes or carries domestic animal disease
-
either directly causes, or indirectly transmits, a disease to a domestic animal
- omnivore
-
an animal that mainly eats all kinds of things, including plants and animals
- 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.
- 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.
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