Why Do Mexican Jumping Beans Jump When They Get Warm ?

by Louis

Mexican Jumping Beans

Mexican Jumping Beans

My child did a science fair project to explain why Mexican jumping beans jump when they get warm. It was really fun and was SO popular with everyone!

We had people hold them in their hands, and as they warmed up, they began to jump. This was done under a lamp, and without any heat or light in darkened cooler to show the different levels of activity of the jumping beans.

Recently I ordered some more for a 'yet to be decided' science project; there are so many possibilities. Check them out, you can now buy Mexican jumping beans online at


Let me know how it goes!

Barry's Response - Sounds like a riot. Thanks Louis.

Shall I let them in on the secret - These seeds have small moth grubs living inside them. When heat is applied to the bean, because the grub twitches from the heat. Even sunlight produces enough of a heat sensation to elicit this reaction.

The larva lives inside and feeds off the inside of the seed for a month or more. Then it goes through its metamorphosisif it survives that long and emerge an adult moth the following spring, with a life span of less than a week afterwards.

They have been marketed as toys (of sort) for decades and you can even find them on eBay. To keep them alive, moisten them well in rain water every couple weeks and keep them relatively cool and dry otherwise. They will die from excessive heat or freezing.

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