How do mantis shrimp punch so fast?

15 May 2018

Question

How do mantis shrimp punch so fast underwater, why doesn't it tear itself apart?

Answer

Cambridge University's Kate Feller took on this marine musing...

Kate - That’s a really good question and actually we don’t know. There are some great biomechanic studying mantis shrimp strikes and their appendages in the States, and they have actually built a model of a mantis shrimp appendage like one of the ones that I have here. The whole thing is exactly the same except for, of course, the material that it’s made out of. They have to try different materials because we only have what humans can make when you make a 3D print or a cast of something. And they found that while they could replicate the actual mechanics of the strike, you end up like when you quickly run your hand through a bucket of water a lot of bubbles will follow your hand from the friction that’s happening - the drag. When you take a video of a mantis shrimp striking underwater, there are no bubbles. It just smoothly goes through the water and the only bubble that forms is this crazy cavitation bubble that is actually a vacuum…

Chris - Which they want?

Kate - Which they want at the point of impact. That’s something that is really cool and would be really nice to know more about.

Chris - Jason?

Jason - I have a more general question: are they prey specific? Are mantis shrimp specialised for a particular type of prey with that strike or are they just opportunists?

Kate - Yes. We generally categorise mantis shrimp into two categories. The spearers, which is like what I have here or in my little shadow box that I brought for ‘show and tell’ Sometimes they’ll have these knarly harpoons...

Chris - Kate’s showing us a bit of a mantis shrimp just for the the jury.

Kate - Yes. I have a shadow box full of weapons - mantis shrimp weapons, and you can see on these larger species they’ve got these huge harpoons, and that’s specialised for stabbing soft bodied prey like fish. And they’ll just stab them and then bring them up to their face and just start eating them whether or not they are dead.

Then the other type of mantis shrimp are what we call the smashers, and these are the ones that are really the world record holders for getting that speed from their strike. The species I have here is an example is super tiny. This is one of those really small species, although these guys can get to be about the 6 inch length size as well. But they have what is essentially on their elbow a big hammer that they will smash hard things with like snails, or crabs, or each other, or rocks.

Chris - So we don’t know. There’s still are a question there about how they manage to move so quickly and not cause these cavitation except where they want it to happen. So there’s important research to be done for you for the next two years Kate. You’ll have to go and find out.


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