Opossum Science

According to a friend’s recent social media post, a 15-pound opossum has been caught under her house in the Los Angeles area.

The responses were an interesting, but typical cross section of America’s modern-day urbanites: one well meaning person commented how beneficial opossums were (and listed a whole range of “pest control” supposedly performed by opossums. Another pleaded to have it released alive in some other place “where it could thrive”. Another was concerned about possible “babies somewhere”, and yet another said how sad it was that the opossum “had to leave its home”. One commenter even inquired if the intent of the capture was to keep it as a pet.

I probably should keep my mouth shut, but the science writer (with some academic background in biology) finds this rather difficult.

The reason why I find this interesting is because here is a good illustration of what the relationship with nature has turned into — as least in big cities. On the one hand we engineer completely synthetic environments with a couple of dispersed token shrubs and sad trees, as if to distract from the fact that we have sealed and suffocated most of the natural Earth beneath our feet. On the other hand, we romanticize every critter and think if it’s alive out there somehow, it must be part of nature and thus, it has every right to be here among us. In a strange twist, we humans are suddenly said to be “encroaching” on the territory of beasts, and not the other way around. This, after we have thoroughly destroyed or at least altered almost every natural habitat on Earth – or perhaps because of it.

There are now city slickers in California who are willing to accept the occasional hiker or resident getting killed or maimed by a bear or mountain lion as if this was just an unfortunate but rare and unavoidable accident. I have even seen bizarre comments not suggesting, but proclaiming it was the home owner’s or hiker’s fault for “being in the animal’s habitat”. “Leave the animals alone,” suggested one. “Nobody needs to live there. Nobody needs to go hiking in the backcountry. That’s why we have gyms.”

People have started to perceive wilderness as if it was just the no-go section of Disneyland, the wild animal zone of the park into which humans should only be allowed with severe restrictions and at their own peril — after obtaining a permit and signing liability waiver and consent forms. And the anthropomorphic worldview of children has not just become mainstream — it is now considered the new normal. This extends also to how mainstream America treats its pets, which, or who, as some have suggested, should be given civil rights independent from their owners.

But back to opossums. What does science really tell us about them?

Being the largest order of marsupials in the Western Hemisphere, they are comprised of 103 or more species in 19 genera. None of them is native to California. 

As far as wildlife zoologists can tell, they were introduced in San Jose in 1910 from the East Coast. They are an invasive species and therefore not well suited to live in the California wilderness at all. Outside of their natural habitat, they are opportunists thriving in or near human habitation, which they exploit. 

The myth that opossums have all these wonderful benefits is greatly exaggerated, and some of these claims are simply false. Some are a mix of fact and fiction. For example, the immune system of opossums is quite remarkable. They seem to have immunity to many snake venoms, which is a topic of scientific inquiry as it may help us to make better anti-venom for victims of snake bites. Opossums also possess a high degree of natural immunity to the rabies virus. While all this is scientifically very interesting, it is incorrect to assume that the presence of opossums will rid the neighborhood of dangerous snakes.

Opossums pose a threat to both wildlife outside their natural habitat, and to domestic pets. In California, the purported benefits of opossums could be had with native animals such as raccoons and skunks, on whose territory opossums encroach.

The University of California’s Integrated Pest Management Program has this to say:

“Opossums are considered a nuisance in gardens and near homes where they feed on berries, grapes, tree fruits and nuts, and defecate on garden paths and patios. They get into fights with dogs and cats and can inflict serious injury with their mouthful of sharp pointed teeth.

Opossums carry diseases such as leptospirosis, tuberculosis, relapsing fever, tularemia, spotted fever, toxoplasmosis, coccidiosis, trichomoniasis, and Chagas disease. They may also be infested with fleas, ticks, mites, and lice. Opossums are hosts for cat and dog fleas, especially in urban environments. This flea infestation on opossums is particularly concerning for transmission of flea-borne typhus, which is increasing in prevalence in Orange and Los Angeles Counties.”

So there you have the scientific truth.

It should be noted that it is illegal to relocate an opossum without a permit. For two reasons: (1) It has virtually no chance of surviving in the California wilderness, but it might introduce new diseases and parasites acquired near humans and from their pets, to wild animals. (2) It can only thrive by scavenging from human habitation, and releasing a captured opossum near someone’s else’s home amounts to gifting the problem to someone else.

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