The Good, the Bad and the…Prawn? – The Pistol Shrimp

For Infinite Variety’s first post I thought I would start off with something very special. The pistol shrimp (snapping shrimp or alpheidae) is a subfamily of caridea (which includes other shrimp and prawns) that is characterized by having one enlarged claw capable of emitting a loud snapping sound. It is a diverse family covering over 600 species and can be found in almost every corner of the ocean, inhabiting self-dug burrows in coral reefs and submerged seagrass flats. Here in these burrows, some members of this unusual branch of shrimp frequently bunk with goby fish, forming an unlikely symbiotic relationship; while the pistol shrimp constructs and maintains the den, the goby fish –with its far superior eyesight– alerts his roommate of any approaching danger with distinguishing flicks of the tail when they then both hide away in the safety of their corralled fortress. However, it isn’t the relationship of this odd couple that we’re interested in but the peculiar weapon that the pistol shrimp wields.

The shrimp locks its claw into place as one would pull back the trigger on a gun to prepare to fire. Then, using the intensely powerful muscles in its grotesquely enlarged claw, the shrimp snaps its claw shut with such a force as to create a shockwave through the water. The pistol shrimp not only uses these snaps as a form of communication with other shrimp, but these shockwaves are so powerful that they can stun or even kill other shrimp or small fish from a distance of up to 4cm away! The shrimp literarily uses it’s ‘pistol’ for hunting!

So how does it do this?

Well, it’s actually all to do with sound. Although the pistol shrimp’s maximum length may not even exceed your little finger, the cacophony of sound that it creates by snapping shut its claw can reach an astounding 240 decibels (a sound pressure almost twice that of a jet engine from 30 meters away!) and due to the acoustic properties of water (sound waves travel through a liquid much more effectively than through the air) can be heard from over a mile away and can even interfere with submarine transmissions. Originally these clicks were thought to be nothing more than the sound of either pincer slamming together at great speeds, but research carried out by both the University of Twente in the Netherlands and the Technical University of Munich discovered something much more interesting: the snap is actually caused by the collapsing cavitation bubble (or bubble implosion) caused by the sudden (the snap lasts no more than a millisecond) increase of immense pressure exerted by the claw as it squeezes together.

*(Here’s a quick basic physics lesson on pressure for you: suppose you have a cylinder full of atoms and a piston pushing down from above. As the piston moves down the atoms are compressed into a smaller space. What happens when an atom hits the moving piston? It picks up speed from the collision as would a stationary ping-pong ball should you hit it with a paddle. This increase in movement (kinetic energy) gets more frequent as more pressure is applied (just as a ping-pong ball would bounce more frequently should you hit it in a smaller space than in a larger one), and so all the atoms in the cylinder will pick up speed and so get ‘hotter’. This is all heat is: the kinetic energy (movement/excited state) of atoms. This means that when we compress gas, the temperature of the gas increases and this is exactly what we see here with the pistol shrimp. When the shrimp’s claw snaps shut, it does so at such a rate that the bubbles of air in the water are compressed as energetic liquid is forced into very small volumes.)

This collapse of the cavitation bubble creates spots of high temperature that emit shock waves, which are the source of noise. However the most incredible part is that the snap can also produce sonoluminescence (light created from the implosion of bubbles in a liquid when excited by sound). As it collapses, the intense pressure means that the interior of the bubble momentarily reaches temperatures of over 5,000 Kelvin (or 4,700 °C). To give you some idea of just how hot that is, the surface temperature of the sun is estimated to be around 5,800 K (5,500 °C)! This was the first observation by a scientist of this type of light production by any animal in nature (although it has subsequently been discovered that the Mantis Shrimp – a close relative to shrimp, but not actually a shrimp at all – is also capable of creating sonoluminescence in a similar fashion, though with a different set of tools).

It has also been discovered that pistol shrimp have the ability to reverse claws. When the snapping claw is lost for whatever reason, the missing limb will regenerate into a smaller claw and the original small claw will grow into a brand new snapping claw, capable of producing the same devastating effect as the lost ‘pistol’.

So if you ever go diving and encounter a pistol shrimp, you’ve got to ask yourself one question: “Do I feel lucky?” Well, do ya, punk?

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6 Comments on “The Good, the Bad and the…Prawn? – The Pistol Shrimp”

  1. Cynthia Says:

    Nice blog and it’s really something i’m interested in, glad you really did it! The first time you are not talking about science or carl sagan lol Anyway, keep going! xxx

  2. Luca Says:

    Cool idea! All the best.

  3. Marta M. Says:

    I want to be the first one to comment.

    But I’m speechless, hahaha.

  4. Jonny Magnolianoses Says:

    Great! An absolute pleasure to read, especially loved the “science bit”.

    It generates sonoluminescence? wow!!

    Questions:

    1. Is it possible for a Pistol Shrimp to take its own life (purposely or inadvertently) from the shockwave it produces (assuming its head is less than 4cm away from it’s claw)?

    2. Does this happen regularly?

    Maybe this is the factor that limits the Pistol Shrimp’s size. If so it might be used as an argument to support the Creationist nuts, as it definitely shows a sense of humour.

    Kind of like the irony of having a gigantic penis (how unholy), where even a slight erection would cause the bearer to pass out as his brain is starved of oxygen.

    3. Did you know that Mantis Shrimp are called “Pissing Shrimp” in Cantonese?


  5. Dear Jonny,

    1)I believe that the shrimps arm joints and claw length forbids it from having the ability to commit suicide and therefore 2) does not happen regularly. And you’re right; if it could commit suicide I’m sure that natural selection would have eventually eradicated all these suicidal shrimp so that the only ones left would be the optimistic kind, making for an all-round better place for pistol shrimp to live.

    Here’s some fun facts for you about penises – the biggest penis on Earth belongs to the Blue Whale and was measured at around 8 feet in length and apparently the animal with the largest penis in relation to body size is the barnacle!

    3) I just wiki’d the Mantis Shrimp in Chinese and found out that you are indeed correct! 攋尿蝦 does translate as ‘pissing shrimp’! How bizzare!

    Thanks for the insightful comments 😉

  6. Jonny Magnolianoses Says:

    There was me thinking the largest penis in relation to body size was the penis-fly, terrifying creature, especially when they swarm.

    Jeeze….eight feet….

    Thanks a lot for getting back to me about the chances of them killing themselves with that lethal claw of theirs.

    I forgot to mention something I found really amazing is what you wrote about if they lose their ginormous claw, the other claw will then grow larger to replace it. Incredible.

    It really makes me wonder, are they all born with a claw on the same hand or are some of them southpaws?

    Can they keep replenishing claws or is their a limit, kinda like their DNA tells them “no way mate, I know your game! you had your designated lot and now you blew it, no more pistols for you!”

    Ive heard two theories as to why they are called “pissing shrimp”, one is that when you catch them they pee (or squirt out a liquid that makes them look like they are peeing). The other is that after they are caught they rely on a chemical in their pee to keep them alive. I don’t know which of these, if any is true.


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