Monday, 13 March 2017

Knitting Shrimp

Image: Moorea Biocode
Is that a gun in your pocket, or are you just settling down for some knitting?

I know it sounds strange, but it's a perfectly reasonable question. Honest!

Image: Moorea Biocode
Alpheus pachychirus
You remember the Pistol Shrimp, don't you? They're the family of small shrimp who use their mega claw to frighten, stun or even kill predatory fish by wielding the power of science. They do it like that *clicks fingers* Except they don't have fingers so they use their mega claw, instead.

It works pretty well! They snap that claw with such force that it forms a cavity - a bubble of vapour, known as a cavitation bubble. It's like a tear in the fabric of the sea. But it can't last because it's surrounded by water. The water doesn't rush into the bubble, it crushes the bubble.

Image: Moorea Biocode
Alpheus clypeatus
The pressure and temperature of the vapour inside rises and rises until the bubble collapses, and all that energy is released in the form of an acoustic wave and a flash of light. It's one of the loudest sounds in the sea. It's also enough to kill small fish and ward away much larger ones.

Not bad for a shrimp who's only 3 to 5 (an inch or two) long! It's also the complete opposite of knitting...

Image: Moorea Biocode
Alpheus bucephalus
Which means it's time to check out the so-called-by-at-least-a-couple-of-people 'Knitting Shrimp.' They are a select few Pistol Shrimp in the genus Alpheus who've learnt to relax. And they relax by knitting a massive sock. Sort of.

Despite their firearms, Pistol Shrimp actually enjoy a bit of peace and quiet. A lot of them like to hide in burrows and crevices where they can escape the dangers of the world. Knitting Shrimp do something a little different. They live in a tube which they construct out of filamentous algae.


You know that old saying about how if you have a hammer, every problem looks like a nail? Luckily, the Knitting Shrimp isn't like that. They have a mega claw, but they don't think every problem looks like a fish face. The next set of limbs behind the big pincers are a pair of smaller, much more flexible pincers. With these they can knit and stitch together the filaments of filamentous algae to build their tube home.

Some Knitting Shrimp also add bits of sponge and coral. It's possible that things like sponge and even the algae may be toxic to predators, providing the Knitting Shrimp with extra protection. Pretty nifty for what is essentially a little blanket.

But don't be fooled! They're still armed with that cavitating mega claw. If you come face to face with a Knitting Shrimp, there's one questions you've got to ask yourself: Do you feel lucky, punk?

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