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How do Mexican jumping beans work? | May 20, 2009


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Hi, I’m Marshall Brain with today’s question.

How do Mexican jumping beans work?

When I was kid growing up in Southern California, my father used to take us to the 7-Eleven on the corner for slurpies and gum. There was usually a display on the counter that held little clear plastic boxes of four or five Mexican jumping beans. You could hear the display rattle as the beans clicked against the plastic boxes. We would buy them, and play games with them on the kitchen table. Mexican jumping beans are very real, but the Mexican jumping beans that you see in many cartoons are not real.

Mexican jumping beans are small, about the size of a kernel of corn or a small bean. They do not wear sombreros. They do not jump into the air. They rock or on occasion, scoot a millimeter or two. Imagine a kernel of corn that moves a millimeter in one direction every 15 seconds or so. That’s about as exciting as jumping beans get. The things that make these beans jump is a tiny moth larva that lives inside the bean. The moth lays its eggs in the flower of the plant, and the eggs are incorporated into the seeds. The larva then eats out the interior of the bean, and lives there. When the larva moves, so does the mean. Eventually, the larva turns into moths that emerge from the beans to repeat the cycle.

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