How do snakes digest big animals?
How can snakes eat and digest animals massively bigger than they are?
Chris Smith asked Jason Head from Cambrudge University to digest this question from Sarah in London. And she wasn't the only one with questions, panelists Stuart Eves and Eleanor Drinkwater had some questions up their sleeve too!
Jason - Well the important thing about snakes and feeding is that other animals will eat prey items larger than they are. So animals will kill other larger animals and eat them. But most animals have the ability to actually break down what they've just killed into small, bite-sized chunks either by tearing at it with their mouths or using their limbs. Snakes of course not having any limbs and having very specialized bodies don't have that luxury. There's only one species that will actually take its prey item, which are crabs, and break them apart in bite-sized chunks and eat the chunks.
Chris - So how does it do it then?
Jason - That snake does that by basically pushing its body against the crab and then grabbing a limb and pulling those pieces off and of course since crabs are jointed and segmented it's fairly easy to do. But for most snakes, the, what they end up having to do is to basically kill a prey item and then get it from outside to inside, which effectively means that the snake is walking over the prey item itself. So it's basically taking its body and moving it over. The specialists for eating big things are boas and pythons. They're the real large prey specialists, and their physiologies are really specialised for building the body up when it's time to eat and then metabolizing the body itself when it's not. So we know from studies of pythons that after they've eaten they actually build up heart muscle, so these animals will build up their hearts, they'll build up the circulatory system, they’ll build up their stomach to digest the animal they've just eaten, some large prey item, and then over the course of having completed digestion thus slowly actually start to metabolize their own body tissues to basically conserve energy and so they have these specialised digestive enzymes where they can completely digest whatever prey item - with mammals it's usually only things that are made of keratin that survive.
Chris -That's the hair isn't it.
Jason - Yeah yeah so hair and nails and everything else is digested by the snake, they’re incredibly efficient.
Chris - Even bone?
Jason - Oh yeah absolutely.
Chris - Good grief! Stuart?
Stuart - So having been at a child's party earlier on and tried to tackle a large piece of cake..
Chris - Hold on! We’re just talking about snakes eating large things
Stuart- I am getting there I'm getting and the question be - how do they breathe? Because, if they're going to walk over, say a ra, presumably that is going to be a relatively large kind of piece of prey. There must be a point where they struggle to breathe. You can see how the party went for me this morning.
Chris - Were you getting tempted to feed a 4 year old to an anaconda?
Stuart - No I tried to eat something that was way larger than I should have.
Jason - It's an interesting question. Well I should say, I don't know if there have been studies that have actually looked at respiration while they feed, certainly bacon go periods of time without breathing. So they can move the prey item down. The trachea and the lungs the snakes are really very very specialized into themselves and I think would be very hard to actually pinch that off.
Chris - Can snakes throw up because if they if they take something in and then they think second thoughts this is bit less digestible than I had in mind.Can they get rid of it.
Jason - They can and they'll do that when they're threatened actually. So, there's lots of videos you can see online of people kind of finding a snake and harassing the snake until it vomits up its prey. It's incredibly damaging to the snake, to do that, so don't ever do that if you see a snake that's just fed.
Chris - I've never seen snake feces, do snakes poo?
Jason - They do. I've kept pythons before it's not enjoyable, but it is just bits of resistant tissues again like hair and nails and then big piles of uric acid.
Chris - Right. So what is it like, a Mr Whippy, 99 Flake sort of action or is it just little bits of debris, because they can't be much left at the end of this?
Jason - It's much more like bird poo than you might think.
Chris - That figures given the evolutionary relationship
Jason - Again you know with some of the more resistant bits in a shall we say more identifiable bolus.
Chris - You were going to ask something Elena?
Elena - Oh this is a really disgusting question, but I've been curious. Once in the jungle we came across a snake and we tried move it off the path, but the person who picked it up, it was still alive. They fell apart and then inside it was this like rotting decaying mouse. And we thought it might be because it got cold and wasn't able to digest it, or would it be that the snake was sick?
Chris Are you saying the snake fell to pieces?
Elena - Yes, iIt was the most horrifying thing I've ever seen before.
Jason - You ran into a very unhealthy snake it sounds like.
Elena - It’s too cold?
Jason - I assume it would I don't know enough about kind of tropical snakes, but I think one of the interesting things about some of the very potent toxic venoms that snakes have. One of the theories behind viper venoms, the rattlesnakes and vipers with those big hypodermic needle like teeth is that that's actually an adaptation for injecting the prey with digestive enzymes in a cool environment where you actually wouldn't be really effective at breaking down the prey item. So what you do is you instead you just give it a shot of digestive juice to begin with.
Chris - A question we get asked quite a bit is is a snake resistant to its own venom. So if a code repeats itself or bit a cobra identical to it would it be vulnerable to its own venom.
Jason - To my understanding yes.