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Why Do Jumping Beans Jump?

delictika's picture

the jumping bean Larva, pupa, and full grown moth along with the opened jumping beanIf you have ever been to Mexico, you sure must have come across the fascinating Jumping beans displayed on the shelves of novelty shops and wondered why and how do these weird jumping beans actually manage to jump! Stop wondering and read on for I have shared the very secret behind these mysterious jumping beans.

Jumping beans to begin with are not beans but a type of seed from a wild Mexican shrub called Sebastiana pavoniana. The secret behind these seeds jumping around is a larva that lives inside these seeds. A type of moth called the Laspeyresia saltitans lays its eggs in the flowers of this plant. As the flowers fade away to form the seeds, the eggs are entrapped within the seeds. The eggs hatch inside the seeds and the larvae feast on the seed for survival. So what is left is just a seed capsule with a live larva inside it. If the larva is allowed to complete its lifecycle, it will form a pupa, develop into a moth, and then break open the seed shell to fly away.

So, now back to the main question, ‘why do jumping beans jump’; the jumping beans don’t really jump or hop, but rather just jerk, wiggle or wobble around (which is equally fascinating!) when held in hand or slightly warmed. This is basically caused due to the jerky movements of the larva inside the bean. Heat and sun can dehydrate the seed and kill the larva inside; hence, whenever the jumping bean capsule is warmed or shaken the larva jumps inside the seed shell causing the "jumping bean to wobble".

If you have been lucky enough to own a few jumping beans then you need to ensure that the seeds do not dry out and kill the larva inside. For this, soak the seeds in chlorine-free (chlorine kills the larva) water once a month. Do not chill, freeze, or boil the seeds – all these actions will kill the larva. However, be forewarned that whatever you do, there will come a time when the larva will develop into a moth and fly away, and the empty seed shell will be all that you will be left with.

Image credits: google.com

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1 Comment

Mamascience's picture
Very interesting! I remember these from when I was a child. They are so much fun.