Opossums (colloquially possums) (Didelphimorphia, /daɪˌdɛlfɨˈmɔrfiə/) make up the largest order of marsupials in the Western Hemisphere, including 103 or more species in 19 genera. They are also commonly called possums, though that term technically refers to Australian fauna of the suborder Phalangeriformes. The Virginia opossum was the first animal to be named an opossum; usage of the name was published in 1610. The word opossum was borrowed from the Virginia Algonquian (Powhatan) language in the form aposoum and ultimately derives from the Proto-Algonquian word *wa˙p- aʔθemw, meaning “white dog” or “white beast/animal”. Opossums probably diverged from the basic South American marsupials in the late Cretaceous or early Paleocene.
Their unspecialized biology, flexible diet and reproductive strategy make them successful colonizers and survivors in diverse locations and conditions.
Didelphimorphs are small to medium-sized marsupials, with the largest just exceeding the size of a large house cat, and the smallest the size of a small mouse. They tend to be semi-arboreal omnivores, although there are many exceptions. Most members of this taxon have long snouts, a narrow braincase, and a prominent sagittal crest.
By mammalian standards, they have a very full jaw. The incisors are very small, the canines large, and the molars are tricuspid.
Didelphimorphs have a plantigrade stance (feet flat on the ground) and the hind feet have an opposable digit with no claw. Like some New World monkeys, opossums have prehensile tails. Like all marsupials, the fur consists of awn hair only, and the females have a pouch. The tail and parts of the feet bear scutes. The stomach is simple, with a small cecum. Notably, the male opossum has a forked penis bearing twin glandes.
Opossums have a remarkably robust immune system, and show partial or total immunity to the venom of rattlesnakes, cottonmouths, and other pit vipers. Opossums are about eight times less likely to carry rabies than wild dogs, and about one in eight hundred opossums are infected with this virus.
Reproduction and life cycle
Further information: Marsupial reproductive system
Sleeping Virginia opossum with babies in her relaxed pouch
As a marsupial, the opossum has a reproductive system including a divided uterus and marsupium, which is the pouch. Opossums do possess a placenta, but it is short-lived, simple in structure, and, unlike that of placental mammals, is not fully functional. The young are therefore born at a very early stage, although the gestation period is similar to many other small marsupials, at only 12 to 14 days. Once born, the offspring must find their way into the marsupium to hold onto and nurse from a teat. The species are moderately sexually dimorphic with males usually being slightly larger, much heavier, and having larger canines than females. The largest difference between the opossum and non-marsupial mammals is the bifurcated penis of the male and bifurcated vagina of the female (the source of the term “didelphimorph,” from the Greek “didelphys,” meaning double-wombed) Opossum spermatozoa exhibit sperm-pairing, forming conjugate pairs in the epidydimis. This may ensure that flagella movement can be accurately coordinated for maximal motility. Conjugate pairs dissociate into separate spermatozoa before fertilization.
Female opossums often give birth to very large numbers of young, most of which fail to attach to a teat, although as many as thirteen young can attach, and therefore survive, depending on species. The young are weaned between 70 and 125 days, when they detach from the teat and leave the pouch. The opossum lifespan is unusually short for a mammal of its size, usually only two to four years. Senescence is rapid. Diet
Didelphimorphs are opportunistic omnivores with a very broad diet. Their diet mainly consists of carrion and many are killed on highways when scavenging for roadkill. They are also known to eat insects, frogs, birds, snakes, small mammals, slugs, and earthworms. Some of their favorite foods are fruits, and they are known to eat avocados, apples, clementines, and persimmons. Their broad diet allows them to take advantage of many sources of food provided by human habitation such as unsecured food waste (garbage) and pet food.
Opossums are usually solitary and nomadic, staying in one area as long as food and water are easily available. Some families will group together in ready-made burrows or even under houses. Though they will temporarily occupy abandoned burrows, they do not dig or put much effort into building their own. As nocturnal animals, they favor dark, secure areas. These areas may be below ground or above.
When threatened or harmed, they will “play possum”, mimicking the appearance and smell of a sick or dead animal. This physiological response is involuntary (like fainting), rather than a conscious act. In the case of baby opossums, however, the brain does not always react this way at the appropriate moment, and therefore they often fail to “play dead” when threatened. When an opossum is “playing possum”, the animal’s lips are drawn back, the teeth are bared, saliva foams around the mouth, the eyes close or half-close, and a foul-smelling fluid is secreted from the anal glands. The stiff, curled form can be prodded, turned over, and even carried away without reaction. The animal will typically regain consciousness after a period of between 40 minutes and 4 hours, a process that begins with slight twitching of the ears.
Adult opossums do not hang from trees by their tails, as sometimes depicted, though babies may dangle temporarily. Their semi-prehensile tails are not strong enough to support a mature adult’s weight. Instead, the opossum uses its tail as a brace and a fifth limb when climbing. The tail is occasionally used as a grip to carry bunches of leaves or bedding materials to the nest. A mother will sometimes carry her young upon her back, where they will cling tightly even when she is climbing or running.
Threatened opossums (especially males) will growl deeply, raising their pitch as the threat becomes more urgent. Males make a clicking “smack” noise out of the side of their mouths as they wander in search of a mate, and females will sometimes repeat the sound in return. When separated or distressed, baby opossums will make a sneezing noise to signal their mother. If threatened, the baby will open its mouth and quietly hiss until the threat is gone.
Hissing or squawking is a defensive process that helps the opossum deter other animals from approaching it.