Attack of the Killer Shrimp
Posted by Richard Conniff on May 2, 2013
This is my latest post for TakePart:
One day early this year, on the Connecticut beach where I have walked most days for the past 15 years, I came across an animal I’d never seen before, washed up in the seaweed. At first, a neighbor and I thought it might be an immature lobster. It was about eight inches long, with a greenish-gray segmented carapace, and goggle eyes mounted on stalks. But in place of a lobster’s formidable claws, it seemed to have only a couple of feathery antennae.
So: Lobster-like, but lame.
Lord, were we ever wrong. It was in fact one of the most violent creatures on Earth, “enchantingly violent,” in the words of a biologist who studies them, violent enough to bring to mind the old “Jaws” soundtrack (DUNT-dunt, DUNT-dunt) and the teaser line: “You’ll never go in the water again!”
It was a mantis shrimp, so named because many people think they look like a cross between a preying mantis and a shrimp, though they are actually members of their own crustacean order, the Stomatopoda. There are about 400 species of mantis shrimp and they inhabit coastlines worldwide, leading mostly solitary lives, typically burrowing in mud and silt on the sea floor, or hiding out in rocky formations.
But let’s get to the violence. Mantis shrimp surveying their world are a bit like the extraterrestrials in the movie Mars Attacks! They can seem momentarily as if they come in peace. Some of them are quite beautiful, with brilliant peacock colors and odd, fluttering anatomical parts. They study the world around them through strange globe-like eyes that rotate independently. Each eye has three pupil-like structures, for trinocular vision. And where human eyes have just three specialized types of cell for detecting color, mantis shrimp have 16. No one knows why, but some mantis shrimp also produce a low-rumbling sound like elephants. Maybe to lull passersby into a state of torpor.
Meanwhile, the jackknife claws tucked up on either side of a mantis shrimp’s head are spring-loaded, and when those eyes detect a suitable prey, the claws catapult out with incredible speed and destructive force. According to the Chesapeake Bay Program, it takes just eight milliseconds, and it ranks among the fastest animal movements on Earth. By comparison, our own “blink of an eye” drags along at about 300 milliseconds.
They strike with a force of 1500 Newtons, about 335 pounds.Depending on their weaponry, different mantis shrimp species get classified as either “smashers” or “spearers.” The smashers have hammer-tipped claws. They strike with a force of 1500 Newtons, about 335 pounds. To put that in perspective, it takes only a little more force—1900 Newtons—for a human karate punch to split a concrete slab an inch-and-a-half thick. More to the point, the hammer can smash open a clam shell or a snail. Some hammer-type mantis shrimp are aggressive enough that if you put one in a standard fish tank, it will burst through the glass (and possibly come hunt you down).
On my beach, where I like to swim, or sometimes just wade around wriggling my feet in the sand, the mantis shrimp (Squilla empusa) is a spearer. When it strikes, it stabs its prey in the heart or rips it to shreds.
So should I worry? Shrimp fishermen and others who sometimes inadvertently pick up S. empusa have, according to a University of Michigan website, dubbed them “thumb splitters,” “finger poppers,” and even “killer shrimp.”
But swimmers have nothing to fear. Instead, mantis shrimp are just one more lovely instance of an essential lesson about the natural world: You do not need to travel to the Serengeti to see incredible acts of predation. You do not need to visit the Amazon to find amazing behaviors of all kinds. Wherever you live, this stuff is happening right there, all around you. All you need to do is look.