First of all, the jumping bean is not actually a bean; it’s a seed. And it doesn’t actually jump; rather, it rolls and tumbles.
The Mexican Jumping bean is really a three-celled bean pod that grows in Chihuahua, Mexico. It is the seed of the yerba de flecha, a Mexican rubber tree plant. The plant’s pod is what the bean moth uses as a home.
When the plant flowers, the moth lays its eggs inside the blossoms. As each blossom develops into a pod, the pod’s meat grows around the egg. When the egg hatches, the larva, or caterpillar, eats away at the meat of the pod, then lines it with silk threads from the spinnerets, or spinning organs, in its head.
Most of the time, the larva is quite comfortable in its silk-lined apartment, but every now and then if the pod is in direct sunlight or if it gets too hot inside, the larva turns and tumbles inside until it has moved into the shade. This turning and tumbling causes the bean to look as if it is jumping.
After several months as a “jumping bean,” the larva passes through the pupa stage, then eats its way through the walls of the bean and emerges as an adult bean moth.