The Virginia opossum is North America’s only native marsupial, often encountered in backyards and urban settings. Their nocturnal nature frequently leads to public concern regarding potential aggression or disease transmission to humans and pets. Although they may appear intimidating, the actual risks posed by opossums are often significantly lower than commonly perceived. Their biology and behavior reveal that these animals are generally non-confrontational and possess natural defenses that minimize their threat profile.
Understanding Opossum Temperament and Behavior
Opossums are solitary and timid animals, driven by an instinct to avoid confrontation with larger creatures, including humans and domestic pets. When they encounter a perceived threat, their first response is to flee and seek shelter. They are not known to be aggressive and rarely initiate an attack unless they are injured or deliberately cornered.
A threatened opossum may exhibit behaviors that appear menacing, such as hissing, drooling, or widely opening its mouth to display its fifty sharp teeth. These actions are defensive bluffs designed to scare away an attacker, serving as a warning rather than preparation for a fight. Such displays are typically fear-based and represent a low-likelihood scenario of a physical attack.
The most well-known defense mechanism is an involuntary physiological response called thanatosis, or “playing dead.” When an opossum is severely stressed or physically attacked, its nervous system triggers a catatonic state. The animal collapses, becomes unresponsive, and may remain in this state for minutes to several hours.
During thanatosis, the opossum’s body enters a tonic immobility where its heart rate and breathing slow dramatically. A foul-smelling fluid is sometimes secreted from its anal glands. This combination of a death-like appearance and repulsive odor deters predators that prefer live prey or instinctively avoid a potentially diseased carcass. The opossum has no control over this reaction, which is a genuine physiological state, not a conscious act.
Because of this deeply ingrained, non-aggressive defense strategy, adult opossums rarely engage in physical fights with dogs or cats. Injuries to pets typically occur when a domestic animal corners or attacks the opossum, forcing it to defend itself with a defensive bite. The risk of an unprovoked attack on a human or pet is exceptionally low.
Disease Transmission and Health Concerns
A widespread misconception is that opossums are carriers of the rabies virus, yet they exhibit a strong, natural resistance to the disease. The virus struggles to survive within their system due to their unusually low average body temperature, which typically ranges between 94 and 97 degrees Fahrenheit. This temperature is below the threshold required for the rabies virus to successfully incubate and spread.
While rabies cases in opossums are extremely rare, they can carry other zoonotic pathogens that pose health risks to humans and pets. Contact with opossum feces or urine can be a vector for bacterial infections such as Leptospirosis. This disease can cause flu-like symptoms and potentially lead to kidney or liver damage in humans and dogs. Contamination typically occurs through exposure to infected water or soil.
Opossums can also transmit several parasitic diseases, including Coccidiosis and Toxoplasmosis. These are spread when the parasites’ microscopic cysts, shed in the opossum’s feces, are ingested by other animals or accidentally by humans. The risk is elevated for pets, particularly dogs, that may ingest contaminated materials in the yard.
Opossums are the definitive host for the protozoan that causes Equine Protozoal Myeloencephalitis (EPM), shedding the parasite through their droppings. Horses contract this serious neurological disease by consuming feed or water contaminated with opossum feces. Their presence near stables is a particular threat to livestock.
Opossums often harbor external parasites, such as fleas, ticks, and mites, which can easily transfer to domestic animals and people. Although they are known for their fastidious grooming habits and may consume a large number of ticks, they still serve as temporary hosts. They can introduce these pests and the diseases they carry, such as Rocky Mountain spotted fever, into a home environment.
Property Damage and Nuisance Behavior
Opossums are nomadic creatures that do not build permanent dens, instead seeking temporary shelter for a few days at a time. They are opportunistic denners and may take up residence in sheltered, dark areas such as under sheds, porches, decks, or occasionally in attics or garages. Their presence in these spaces is generally a nuisance rather than a threat to the structure itself.
Unlike raccoons and rodents, opossums are not known to chew through wood, wiring, or other building materials to gain entry. They are more likely to use existing openings or gaps around foundations and roof lines. Their primary nuisance involves the mess they create through their scavenging habits and the sheer volume of their waste, which can be large and scattered haphazardly.
Their omnivorous diet leads them to seek out easy food sources, causing problems for homeowners. They frequently rummage through unsecured garbage cans, consume fallen fruit from gardens, and readily eat pet food left outdoors. The accumulation of their droppings and the possibility of a carcass dying in a hidden space are the most common and foul-smelling problems associated with their denning.