Gregory Dietl of Yale University and colleagues found that snails with left-handed cones are impossible for predators to eat.
They found the crab is unable to open left-handed shells because it only has a tool for peeling them on its right claw; so it discards them.
"The crabs have a special tool on their claw, a tooth that's used like a can-opener," said Gregory Dietl from Yale University.
"So, if you imagine trying to use a right-handed can-opener with your left hand - it's very hard to do," he told the BBC News website.
Despite this evolutionary advantage, however, left-handed forms remain rare.