Science Questions

After watching the TV series “Life in Cold Blood” I was wondering how the venomous snakes didn’t poison themselves when they ate their prey. I know they’re not immune to their poison because they don’t use it on each other when they fight for their territory battles for example. I know if animals like ourselves ate food that had been poisoned it would have an adverse effect on us but it doesn’t seem to on snakes. I just wondered why that was, really. Beth

The reason is that the venom snakes use is a protein. Proteins are made up of building blocks of what’s called amino acids. They’re the same stuff, effectively, as your Sunday roast: meat. That means that if you were to eat them – say I ate a snake and ate the poison sacks – if I just ate it and it went into my digestive system the acid and the enzymes in my stomach would just be able to break down the protein so it would fall apart and it would be harmless. It’s only actually toxic if it gets beyond the gut and it gets into the circulation of the body. That’s why one snake could, for instance, eat another snake, and it wouldn’t be poisoned by it. In the same way, a person who has diabetes and needs to inject the hormone insulin. Insulin is a protein and if you were to eat it by mouth the digestive tract would break it down. That’s why people have to inject insulin to make it work. So why don’t snakes poison themselves given they have the same toxin in their bodies. It’s exactly the same reason if for instance your pancreas makes a deadly cocktail of digestive juices which, if they got into your bloodstream, would kill you very rapidly. People who get a condition called acute pancreatitis do have a very high mortality rate. It does kill people because they literally eat themselves from the inside out. The reason that they don’t do that normally when you’re healthy is because the enzymes are made in cells in an inactive state. They’re exported from the cell into a duct which is lined with specially protecting cells that stop it going back in to the body’s own tissues and do any damage. The only place it can go is down the duct and then out into the digestive tract. If you put that into the context of the snake, it’s got a gland which knows how to make the proteins in the venom. They get exported into this duct which is a special holding bay, protected from the venom. It can’t go back the wrong way. When the snake bites you there are tiny muscle cells around those ducts and it squirts the venom down the fang (there’s a duct in there) and in to the holes that the teeth have made in you. That’s why the snake doesn’t die from its own venom because it keeps it in a specially adapted part of the body so it can’t get into the circulation. I did ask a snake venom researcher and he said you can also find snake venom antibodies in snakes to their own venom, to a certain extent. They kind of have their own antivenom built it. Possibly because they have exposed themselves at low level. I don’t know how protective that is so there’s two mechanisms there why a snake doesn’t poison itself.

April 2008