Mammals
Virginia Opossum
Didelphis virginiana · also called virginia opossum, north american opossum, possum
The Virginia opossum is the only marsupial in North America — a grizzled, pointy-faced, prehensile-tailed animal that carries its bee-sized young in a pouch and then on its back. It has more teeth than any other land mammal on the continent, shrugs off the venom of rattlesnakes, and, when truly frightened, keels over and “plays dead” whether it wants to or not.
Overview
The Virginia opossum ranges from Central America north into southern Canada, in woodland, farmland, scrub, and suburbs. It is about the size of a large house cat, grizzled grey, with a pointed pink face, thin black ears, and a naked scaly prehensile tail. It eats almost anything — carrion, insects, fruit, eggs, and rubbish.
Fifty teeth, and a bluff
It has 50 teeth, the most of any North American land mammal, and it bares them, hisses, and drools as a threat. If the bluff fails and the fear is extreme, it collapses into thanatosis — rigid, open-mouthed, unresponsive, and leaking a foul secretion that smells of decay. This is a reflex it cannot start or stop at will, so an opossum found “dead” should simply be left alone to recover.
Venom resistance
The opossum is largely unharmed by the venom of rattlesnakes, copperheads, and cottonmouths, thanks to a blood protein now being studied as a possible universal antivenom. Its low body temperature also makes it a poor host for rabies.
Status
The Virginia opossum is Least Concern and expanding, spreading north with warmer winters, limited mainly by frostbite to its bare ears and tail. The widely repeated claim that it eats thousands of ticks a week is not supported by field studies.
Virginia Opossum: common questions
Is an opossum the same as a possum?
In North America the two words are used interchangeably for this animal, the Virginia opossum, which is the only marsupial that occurs north of Mexico. Elsewhere the distinction matters. Possum, without the o, properly refers to a completely different group of marsupials in Australia and New Guinea, such as the brushtail possum and the sugar glider, which are not closely related to the American opossums at all. The shared name is a historical accident, with early European colonists in Australia borrowing a word they already knew from North America for a superficially similar animal.
Why do opossums play dead, and can they choose to?
Playing dead, or thanatosis, is a defence against predators that lose interest in prey that is not moving or that smells rotten. In the opossum it is largely involuntary. Extreme fear triggers a nervous-system response that makes the animal keel over, go stiff, let its tongue loll, and release a putrid fluid from glands near the tail. The opossum is not consciously acting; it cannot decide to do it and, importantly, cannot decide to stop, so an opossum found in this state on a road or in a yard should be left completely alone for an hour or more to recover on its own.
Do opossums really eat thousands of ticks?
The popular claim that a single opossum kills around 5,000 ticks a week comes from one laboratory study in which captive opossums were deliberately covered in ticks and groomed most of them off. A field study published in 2021 found that wild opossums actually eat very few ticks and that ticks are a negligible part of their diet. Opossums are meticulous groomers and probably do remove some ticks from their own bodies, but the idea that they roam the landscape hoovering up ticks and dramatically reducing disease risk is not supported by the evidence.
Are opossums dangerous to people or pets?
Very little. An opossum is slow, has poor eyesight, and its whole defensive repertoire is bluff, from hissing and showing its teeth to drooling and finally playing dead; it will almost always try to leave rather than fight. It can bite if grabbed, and like any wild animal it can carry parasites and diseases, though notably not usually rabies. It may raid a hen house or a pet bowl and can frighten a dog into a scuffle, but it is not aggressive, and the main risk in an encounter is to the opossum.