Is it a Magic Bean? The Story of the Mexican Jumping Bean

Did you get “mexican jumping beans” as a kid? Did you watch in awe as this little bean wriggled over your kitchen table, wondering what this magic was?

TMexican jumping beans are not beans but actually caterpillars. They are Cydia deshaisiana moth caterpillars maturing in the fallen seedpods of Sebastiania shrubs, which thrive in the hot, dry Mexican climate.

The caterpillar in the bean reacts to light and heat, violently jerking its body in an attempt to seek shade, causing the seed to jump. It only stops moving when it is out of the sun’s dangerous, drying glare. Leaving the beans in heat can kill the larva.

The beans come from the shrub Sebastiania pavoniana, often also referred to as "jumping bean".

In the spring, when the shrub is flowering, moths lay their eggs on the shrub's hanging seedpods. When the eggs hatch, tiny larvae bore into the immature green pods and begin to devour the seeds.

The pods ripen, fall to the ground and separate into three smaller segments, and those segments are called Mexican jumping beans. As the tiny larvae inside curl up and uncurl, they hit the capsule's wall with their heads – and the bean jumps.

After the pupal stage, the silver-grey adult moth eats its way out of the seedpod, and the cycle starts again.