Monday, December 5, 2011

The Mighty Opossum

Opossum- MDC Photograph
Opossums seem to me to be the Rodney Dangerfields of Missouri mammals- they don't get no respect.  When I read this story at they went up in my opinion.  Would you believe that this hissing marsupial, whose main defense is to play dead, eats venomous snakes and has some immunity to their toxins?  Snake venom contains multiple toxins including proteins that block blood coagulation, causing their victims to bleed to death internally.

According to MDC, our common opossum, Didelphis virginiana, is an omnivore which eats insects, reptiles, frogs, crayfish, bird eggs and earthworms as well as browsing garbage cans.  Oh, and apparently, the odd rattlesnake and copperhead.  They have co-evolved with these pit vipers and thus developed a defense against their venom. It has previously been thought that snake venom evolved just as a tool to capture prey, but it also seems to be a defensive mechanism against predators. 

A key clotting factor is called von Willebrand's factor and our opossum is one of a few related species that has a gene that has rapidly evolved to affect it, further blocking the effect of the toxin.  Studies indicate that it is undergoing much more rapid selection than usual.  To quote Robert Voss, Curator of Mammalogy at the American Museum of Natural History, "We've known for years that the venom genes evolve rapidly in snakes, but the partner in this arms race was unknown until now.  Opossums eat snakes because they can."  This means that the snakes are prey rather than predator in this circumstance.

 The full study with further details is at and information on the opossum antivenom is at this site.


  1. Opossums have always been my favorite mammal in Missouri. I love doing programs about them and changing the misconceptions of an animal that you so eloquently claimed and with much truth,"gets no respect". I however had NO IDEA they had immunity to snake venom. It just goes to show, we learn something new everyday. I simply cannot wait to add this tidbit to my programs.

  2. So, how many possums do possum-eating Ozarkians need to ingest weekly in order to pick up an immunity to snake venom?

  3. George:
    Two a week but they must be eaten raw.

    NOT! But more interesting is from a recent obituary of Bill Haast, a reptile specialists who died this June at age 101 of natural causes. He had been bitten 172 times by venomous snakes he handled and "milked" for their venom. He had his wife inject him daily with small amounts of venom. (I am not showing this to my wife.) His story is at,

  4. No I did not know that . Fascinating!