Opossums and Venoms – Interesting Facts
Opossums belong to the oldest surviving marsupials: their ancestors appeared near the end of the Cretaceous period around 66 million years ago, and their overall build has changed surprisingly little over the millennia.
Once opossum joeys outgrow the pouch, they climb onto their mother’s back
Today there are more than a hundred species of opossums across North and South America. The trait that has long fascinated biologists and toxicologists is their remarkable resistance to snake venoms and certain biological toxins.
Where the Names “Chucha” and “Opossum” Come From
The first detailed European account of South American opossums was written by the Spanish chronicler Pedro Cieza de León in his 1553 book Crónica del Perú. He compared the animal to a small fox with a long tail, short legs, and brownish fur, and described a female that quickly tucked seven joeys into her pouch and slipped away when people approached. Locals in the region called the creature chucha – a name still used today in Colombia and Peru.
The familiar English word “opossum” comes from a completely different, North American source. In the early 17th century, English colonists in Virginia borrowed it from Algonquian languages: the word apassum (recorded by settlers as opassum) meant roughly “white beast” or “white dog-like animal” and referred to the Virginia opossum.
Anatomy, Behavior, and Joeys
The teeth, limbs, and pouch of opossums still preserve archaic traits of early mammals. Even so, these animals are remarkably adaptable both in the wild and right alongside humans:
- 50 teeth: Opossums have the most complete set of teeth among American marsupials – 50 sharp teeth built to handle a wide variety of foods.
- Playing dead: When severely frightened or injured, an opossum slips into an involuntary stupor known as thanatosis. Its eyes glaze over, foam may appear around the mouth, and its anal glands release a foul smell of decay, causing many predators to lose interest and walk away.
- Tiny newborns: Babies are born roughly the size of a honeybee or a small bean, so 15 to 20 newborns really can fit into a teaspoon. As they grow too large for the pouch, they cling to the fur on their mother’s back and belly.
- Omnivorous diet: Their menu includes insects, small reptiles and amphibians, eggs, fruit, berries, carrion, and household scraps raided from trash cans.
The Virginia opossum is the only marsupial widely established in North America
Why Opossums Resist Snake Venoms
Opossum venom resistance is not some mythical immunity to “every poison on earth,” but the result of specific protective proteins circulating in their blood serum. Two biochemical mechanisms are especially well studied:
- LTNF protein: Lethal Toxin-Neutralizing Factor (~63–68 kDa), a serum protein that binds and neutralizes a range of protein-based animal and plant toxins.
- DM43 and oprin inhibitors: Serum proteins (DM43 in the South American Didelphis marsupialis and the related oprin in the Virginia opossum, Didelphis virginiana) that selectively block snake venom metalloproteinases (SVMPs) – the enzymes mainly responsible for tissue damage and hemorrhage in hemotoxic venoms.
- What venoms it counters: Primarily pit viper venoms (rattlesnakes, copperheads, and lanceheads of the genus Bothrops), which share habitats across the Americas where opossums regularly hunt snakes and get bitten themselves.