The opossum (Didelphis virginianas) is a truly remarkable creature. Although many consider them to be ugly, even sinister looking, (the author is not among those) they possess no small number of amazing adaptations. There are a few superlatives: Opossums have the largest number of teeth of any North American animal – 50 of them – perfect for devouring well…anything. They are opportunistic omnivores, so invertebrates, rotten fallen fruit and other plant material, mice, carrion and garbage are all on the menu. Opossums have one of the smallest brain-to body mass ratios, and yet they are a successful species that has greatly expanded its range from more southern areas. Opossums are our only native marsupial and carry their 7 to 8 bean size newborns in a pouch.
“Playing” possum is their most well-known adaptation. It is far more than just pretending to be dead. It is an involuntary physiological response to severe stress. When threatened, most animals simply run away. Opossums will run away too, but they also have another strategy of falling to one side, mouth agape, exuding foamy saliva and nasal discharge that makes them look sick. Their heart rate and respiration slow, they urinate, defecate, and just plain smell bad. This is certainly a good deterrent to any predator that would prefer their meat fresher and livelier than a comatose opossum appears to be. The charade may last up to 4 hours; certainly long enough to fool any predator that is stimulated by a chase.
Other adaptations are equally impressive. Opossums are 8-10 times LESS likely to carry rabies than most other mammals. Since they are marsupials they have a lower body temperature (94-97 F) which is so low that the rabies virus simply cannot survive. They have a very strong immune system; also advantageous considering the types of food they eat.
Opossums have been found to be a significant predator of ticks that cause Lyme disease. They are fastidious groomers, much like a cat. Any tick that hops on an opossum will most likely be found and consumed as it cleans its fur. Extrapolating the numbers from laboratory studies, it is possible for an opossum to consume about 5,000 ticks in a season – best tick control ever!
Even more fascinating is the opossum’s apparent immunity to venomous snake bites. Researchers have found that a peptide (small chain of amino acids) in the blood of opossums could neutralize snake venom. This peptide has been synthesized in a laboratory and then injected into mice that had been injected with venom from either a diamondback rattlesnake or a Russell’s viper (indigenous to Pakistan). The mice were protected from any ill effects. The theory is that the opossum peptide binds to a protein in the snake venom and renders it harmless. Opossum blood may contain the potential to develop a universal anti-venom which would help to treat snakebites and save lives. It is estimated that 421,000 people are bitten by venomous snakes world-wide each year with about 20,000 deaths. Furthermore, opossums have shown to have a resistance to toxins such as botulism, scorpion and bee stings. There is certainly much more to these remarkable creatures than just “playing possum”!
It’s spring and you may start to see opossum and other animals starting to roam around. Always remember that the best thing to do is to leave them alone – even if it appears to be an abandoned baby. If you do find an animal that is sick or injured, or if you need help deciding what to do, you can find a local wildlife rehabilitator here, or check out the work of Wolcottsville Wildlife, a local wildlife rehabilitator here.