The Virginia Opossum (Didelphis virginiana) is the only marsupial species found in North America north of Mexico. This mammal, a member of the family Didelphidae, represents a lineage that diverged from placental mammals millions of years ago.
Physical Characteristics of the Virginia Opossum
The Virginia Opossum is generally about the size of a domestic house cat, with adults typically weighing between 4.4 and 6.6 pounds. Its body is covered in a coarse coat of grayish-white fur, which is often thicker in northern populations for insulation. It is characterized by a long, pointed snout and a pair of large, dark eyes.
One of the most distinctive anatomical features is its long, scaly, and nearly hairless prehensile tail, which is used to grasp branches while climbing. This tail, along with the thin, naked ears, is particularly susceptible to frostbite in colder climates. Its dark hind feet possess a clawless, thumblike, opposable innermost toe, known as a hallux, which aids in climbing and maneuvering in trees.
Defining Marsupial Traits
The opossum’s classification as a marsupial stems from its reproductive biology, which differs from placental mammals. Following mating, the gestation period is extremely short, lasting only about 12 to 14 days. This brief development time is due to the female possessing a non-invasive, short-lived placenta, unlike the fully functional placenta found in other North American mammals.
The young are born in an altricial, or underdeveloped, state, appearing embryonic and hairless, and weighing only about 0.13 grams, roughly the size of a bee. Immediately upon birth, these tiny newborns must climb up the mother’s abdomen to reach the pouch. Inside the pouch, the young firmly attach themselves to one of the mother’s teats, which then swells in their mouth, keeping them secured for continuous nursing and development.
The mother typically has 13 teats inside the pouch, which limits the number of young that can survive, despite litters often exceeding that number. The young remain attached for approximately two months, continuing their development within the warmth and protection of the pouch. They eventually detach and begin to venture out, often riding on the mother’s back before becoming fully independent.
Survival Tactics and Diet
When threatened by a predator, the Virginia Opossum employs an involuntary defense mechanism known as thanatosis, or “playing possum.” This is not a conscious act but a catatonic, shock-induced state that causes the animal to fall over, become stiff, and appear dead. Accompanying this feigned death is drooling and the release of a foul-smelling, greenish fluid from its anal glands, which further suggests illness or decay to a potential attacker.
This defense can last for several minutes up to several hours, and the goal is to deter a predator that prefers to kill its prey rather than scavenge carrion. The opossum is an adaptable omnivore, consuming a broad diet that changes with the seasons and available resources. Its foraging includes insects, snails, fruits, nuts, small rodents, eggs, and carrion.
The opossum’s role in the ecosystem is notable, partly due to its fastidious self-grooming habits. Studies indicate that a significant number of ticks that attach to an opossum are groomed off and ingested, reducing the local tick population. This behavior highlights the animal’s function as a biological control agent.
North American Range and Habitat
The historical range of the Virginia Opossum was concentrated in the southeastern United States and Central America, but it has steadily expanded northward over the last century. Today, this adaptable species can be found across much of the United States, extending as far north as southern Ontario in Canada. This expansion has been facilitated by human-altered environments, which provide abundant food sources and shelter.
The animal is a habitat generalist, thriving in wooded areas, farmlands, and in suburban and urban environments near a source of water. Despite its poor physiological adaptation to severe cold, including its largely hairless tail and ears which are susceptible to frostbite, the opossum has succeeded in colder regions. Its survival in the northern limits is aided by its ability to take shelter and reduce activity during extreme temperature drops, rather than hibernating.