Opossums Look Alarming but Rarely Deserve the Reputation

A hissing, baring-teeth opossum caught under a deck or in a shed at night looks genuinely threatening. The reality is closer to the opposite: opossums are North America's only marsupial, they're generally non-aggressive, and several of the most widely repeated claims about them — that they're a major natural tick-control agent, and that they're effectively immune to rabies — turn out to be more complicated than the popular version suggests.

What actually identifies an opossum

Virginia opossums (Didelphis virginiana) are roughly house-cat sized, with Purdue Extension and UF/IFAS giving weight ranges in the 4 to 12 pound range depending on sex and individual. Alabama Cooperative Extension describes the face as white with a dark V-shaped marking, paired with black, hairless, leathery ears and a mostly hairless, prehensile tail used for grip and balance. Purdue Extension notes they have roughly 50 teeth — more than most North American mammals — and a distinctive clawless, opposable "thumb" toe on each hind foot.

The tick-eating claim doesn't hold up as well as its reputation

The widely repeated claim that a single opossum can eat several thousand ticks in a season traces back to a Cary Institute study that caged a small number of opossums (alongside other animals like squirrels and mice) and measured how many larval ticks placed on them were groomed off over several days — the opossums removed roughly 83 to 96.5 percent of the ticks in that controlled setting. That lab grooming-removal rate was subsequently extrapolated by others into the popular "thousands of ticks per season" figure, but the original study didn't actually count ticks eaten by opossums living and foraging in the wild. A 2021 University of Illinois study examined the stomach contents of 32 wild opossums directly and found zero ticks in any of them. Massachusetts state wildlife officials now state plainly that research doesn't support opossums meaningfully reducing tick populations the way the popular claim implies. None of this means an opossum never eats a tick — grooming behavior that removes ticks from its own fur is well documented — but the specific statistic behind the reputation rests on a lab measurement that was never designed to represent real-world tick consumption.

Rabies risk is low, not zero

Opossums are frequently described as resistant to rabies, and the Missouri Department of Conservation confirms this framing directly. A CDC-hosted research paper proposes the animal's unusually low body temperature, typically in the 94 to 97°F range, as a plausible reason the rabies virus doesn't establish itself as readily in opossums as it does in many other mammals — but the same paper is explicit that this is a proposed explanation, not a settled mechanism, and that rabies in opossums isn't nonexistent: a surveyed population in Brazil found the virus present in roughly 1.6 percent of animals tested. The accurate framing is "low risk, well below raccoons and other common rabies vectors," not "immune." Any actual bite or scratch from an opossum, as with any wild animal, still warrants prompt medical evaluation rather than being dismissed based on the species' generally lower risk profile.

Why the hissing display is mostly bluff

When genuinely cornered and unable to retreat, an opossum's actual defense isn't fighting — it's thanatosis, the "playing possum" response. The Missouri Department of Conservation describes the animal collapsing, appearing dead, with breathing that slows and drool or snot bubbles sometimes visible, a response that functions as an involuntary, fainting-like physiological reaction rather than a deliberate performance. The animal typically remains in that state for anywhere from a few minutes to a few hours before reviving once the perceived threat has passed. The hissing, open-mouth display people associate with opossums as aggressive is a bluff that generally precedes this collapse rather than an indicator the animal intends to attack.

Why they end up near homes, and what to do about it

Opossums are opportunistic omnivores — Massachusetts state wildlife officials list eggs, grains, nuts, fruit, birds, snakes, frogs, small rodents, and carrion among their natural diet, and they'll readily eat pet food left outdoors or garbage when it's accessible, which is a large part of why they show up around homes in the first place. They also don't maintain a single permanent den the way some wildlife does; University of Nebraska Extension and county-level wildlife guidance both describe them using multiple temporary shelter sites — under decks, in sheds, in crawlspaces — rather than actively trying to move into a structure the way a nesting rodent might. This distinction matters for how exclusion should be handled: Nebraska Extension recommends confirming a den site is actually empty, using gentle light or noise to encourage the animal to leave on its own, and then sealing the gap with hardware cloth or similar material rather than sealing an occupied den shut. County wildlife guidance adds a simple confirmation check — loosely covering a suspected entry point with debris and checking whether it's been disturbed before permanently closing it off.

• Opossums are North America's only marsupial, roughly house-cat sized, with a white face, dark eye markings, and a hairless prehensile tail.
• The popular "eats thousands of ticks a season" claim traces to a lab grooming study never designed to measure wild tick consumption — a 2021 study found zero ticks in 32 wild opossums' stomachs.
• Opossums have notably low rabies susceptibility, possibly linked to their low body temperature, but the risk is low rather than zero.
• Their main defense, "playing possum," is an involuntary collapse response, not a deliberate act — the hissing and teeth-baring that often precede it are bluff, not an attack signal.
• They use multiple temporary shelter sites rather than one permanent den; confirming a site is empty before sealing it is the extension-recommended exclusion approach.

An opossum sheltering under a deck or porch is usually a temporary, low-risk situation rather than an emergency. A free Sevacorp inspection can help confirm what's actually present and the right way to exclude it.

• Sources:
• Purdue Extension — "Virginia Opossum" (FNR-413-W) — https://www.extension.purdue.edu/extmedia/fnr/fnr-413-w.pdf
• Alabama Cooperative Extension System — "Virginia Opossum: Our Only Native Marsupial" — https://www.aces.edu/blog/topics/forestry-wildlife/virginia-opossum-our-only-native-marsupial/
• University of Florida/IFAS — "Virginia Opossum" (UW471) — https://edis.ifas.ufl.edu/publication/UW471/pdf
• Cary Institute of Ecosystem Studies — "Opossums - Killers of Ticks" — https://www.caryinstitute.org/news-insights/media-coverage/opossums-killers-ticks
• Snopes — "Do Opossums Kill Ticks and Inhibit the Spread of Lyme Disease?" — https://www.snopes.com/fact-check/opossums-kill-ticks-inhibit-the-spread-of-lyme-disease/
• Massachusetts Division of Fisheries and Wildlife — "Opossum, More Like Op-Awesome" — https://www.mass.gov/news/opossum-more-like-op-awesome
• Missouri Department of Conservation — "Awesome Opossums" — https://mdc.mo.gov/magazines/conservationist/2019-08/awesome-opossums
• University of Nebraska-Lincoln, Backyard Farmer — "Opossum" — https://byf.unl.edu/opossum