Saturday, August 13, 2011

The Possum and the Horseshoe Crab

This week I read an article which referenced a 1999 article in the Journal of Venomous Animals and Toxins about how some mammals are resistant to venom.  These include the opossum, mongoose, meerkat and hedgehog.

Some of us are familiar with meerkats thanks to the Animal Planet show Meerkat Manor.  Rudyard Kipling's classic story Rikki Tikki Tavi from THE JUNGLE BOOK introduced millions to the lightning quick mongoose, and possums and hedgehogs are fairly common in some parts of the world.

It makes sense that possums would develop a resistance to snakes found in their local area.  After all, snakes would find a baby possum just as tasty as a mouse or rat.  But I was surprised to read that possums sometimes eat snakes.  So the competition between the two may also have spurred possums to develop this resistance.

The article mentioned that by examining the components of a possum's blood, scientists might be able to create a universal vaccine or antidote to venom.  This way, it would not be necessary to identify the type of snake after someone is bitten.  However, I don't believe all snake venom works the same way.  And just because a possum in the US has developed resistance to diamondback rattlesnakes found in its area, doesn't mean it would resist venom from an Indian cobra. 

In a related article, the August 2011 issue of National Geographic has a story about using blood from live horseshoe crabs to screen for bacteria.  The blue, copper-rich blood of these crabs is effective at finding harmful bacteria in vaccines and IV fluids.  Luna Shyr's article points out that the crab blood can detect bacterial amounts of one part per trillion, which is amazing.

After blood is extracted, the crabs are returned to the ocean, with a mortality rate of 15 percent.  Horseshoe crabs have been around since before the dinosaurs.  I don't know what the impact of this blood collection is on their total population, but if we want to continue to benefit from its use, perhaps we'd better learn to keep more of them alive? In the same way, I see a lot of dead possums in the road, killed by cars.

We should preserve the animals around us simply because they exist.  However, these two are not attractive animals.  It's one thing to get people to save cute puppies, but possums look like big rats, and horseshoe crabs look like face suckers from the Alien movies.  However, if we find a use for them like the horseshoe crab's blood, it may give people incentive to keep them alive.  Yes, it's a commercial approach, but when something has obvious value it makes it easier to argue for saving it.  And maybe that's what it takes to save humble creatures like the possum and the horseshoe crab.

(The possum pic is from the National Park Service, and the horseshoe crab pic is from Thomas' Marine Biology Blog.)

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