Southpaw Snails 'Dodge' Right-Handed Crabs

Just as southpaw baseball pitchers confuse right handed-hitters, and left-handed boxers throw punches from surprising angles, southpaw snails are more likely than their right-handed cousins to survive attack by hungry right-handed crabs — a new discovery that's not at all what scientists expected.

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It's DAY TO DAY, from NPR News. Sports fans know that left-handed boxers and southpaw baseball pitchers often have an advantage over their right-handed opponents. Now, new research says that being a lefty can also be a big help if you are a snail. NPR's David Malakoff reports.

DAVID MALAKOFF, reporting:

Let's start with the obvious. Snails don't have hands, but they do have shells, and it turns out that a shell can spiral to the right--that's right-handed--or to the left. Now, if you poke around in nature, biologist Gregory Dietl of Yale University says you won't find many southpaw snails.

Professor GREGORY DIETL (Biologist, Yale University): If I were to make a bet and say you were going somewhere in the world, more than likely every snail you're going to pick up is going to be right-handed. It's a pattern that's been around for a long, long time.

MALAKOFF: Dietl says nobody really knows why there are so few species of left-handed snails. The conventional wisdom was that it shouldn't matter which way a shell curved. But a few years ago, Dietl began to wonder about that conventional wisdom.

He was in Florida studying some sea going snails that happened to be lefties, and he noticed something. The crabs that like to crush and eat snails tend to have powerful right claws. That reminded Dietl, who's also a righty, of sports.

Professor DIETL: Having played sports myself as a child, remembered that there's, you know, this thing of this left-handed advantage. So, I thought, well, let's try and look at this a little bit more.

MALAKOFF: And what sports did you play?

Professor DIETL: I played baseball.

MALAKOFF: How did you like hitting against left-handed pitchers?

Professor DIETL: I wasn't very good at it.

MALAKOFF: So he wondered, do right-handed crabs have a problem when facing a left-handed snail? To find out, first he went back in time. His team rounded up nearly 2000 fossil snail shells. Most were three or four million years old, and about half were lefty species and half righties.

Then the researchers looked at every shell. They wanted to see, did ancient crabs prefer to attack the right-handed snails or the lefties? What they found is that the right-handed shells had far more scars, meaning far more crab attacks.

Professor DIETL: So it's kind of like being a detective almost, when you go back into the past. Each shell tells a story to me.

MALAKOFF: To figure out why the right-handed crabs couldn't handle lefty snails, Dietl decided to do an experiment. He got an aquarium, put in some hungry crabs, and then added some right-handed snails and a few southpaws. Then he watched the crabs attack.

Professor DIETL: And, when picking up the left-handed ones, it was in an awkward position. They would just abandon them, and just say forget it and go move on.

MALAKOFF: Dietl says it was clear that the crabs just were not equipped to handle left-handed shells.

Professor DIETL: This particular crab has a tooth on its claw that it uses almost like a can opener. So it inserts that within the aperture of this snail.

MALAKOFF: It's like a left-handed person trying to use a right-handed can opener, he says. It just doesn't work. Now, Dietl's discovery solves one mystery, but it creates another. Remember, the biologist couldn't see why being a lefty would help a snail survive. Now, the question is if being left-handed prevents you from getting eaten, why aren't there more left-handed snails?

Professor DIETL: This is something that has boggled the minds of malacologists, or naturalists in general, forever. And maybe I've made it a little more complicated, I don't know.

MALAKOFF: Dietl's study appears in the journal Biology Letters, which is published by Britain's Royal Society. David Malakoff, NPR News.

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