Why Did the Mexican Jumping Bean Jump? | Deep Look
53,735To find its place in the shade! Each hollowed-out seed is home to a head-banging moth larva, just trying to survive the harsh Sonoran Desert sun.
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Often sold as novelty items and exported worldwide, Mexican jumping beans are actually the seed capsules of a shrub (Sebastiania pavoniana) that have been taken over by the tiny larvae of an attractive grey moth (Cydia saltitans). The moth lays its eggs on the green immature capsule of female flowers in the spring and summer, and the immature larvae bore into the young seed capsules.
The developing seed will be home and food for the larva as it grows. By late summer, the capsules separate into three sections, falling to the ground. The seed capsules with larvae inside them hop around on the ground, to avoid overheating in the harsh sun of the Sonoran Desert. To do this, each larva weaves a silk lining along the seed interior, grabs on with its hind legs, and thrashes its head against the walls. The force topples the seed, as the larva uses its finely-tuned sense of temperature to seek shade.
After spending most of its life shimmying around inside the seed capsule, the larva transforms into a pupa, and eventually into an adult moth. The moth only has a few days to quickly find a mate and lay eggs on another Mexican jumping bean bush before it dies. With luck, the young larvae will hop another day in the shade.
--- Where do Mexican jumping beans come from?
Mexican jumping beans are found primarily in the semi-arid mountainous regions of the Sonoran Desert in northern Mexico. They also occur in the Mexican state of Sinaloa and as far south as Costa Rica.
--- Can the Mexican jumping bean moths survive in other places?
If the adult moth does not find a Sebastiania pavoniana shrub, then it will die without passing on another generation. The moth has co-evolved with the Mexican jumping bean bush and depends on it for survival. So far, the bush and the moth are not endangered, but the supply is not limitless.
--- Are there other kinds of jumping beans in the world?
In the same family, the Tamboti tree in Africa also produces jumping beans, sometimes called “African jumping beans.” Also, there are other kinds of jumping galls, some of which are inhabited by gall wasps (see our gall wasp episode below).
---+ Find additional resources and a transcript on KQED Science:
https://www.kqed.org/science/1973307/why-did-the-mexican-jumping-bean-jump
---+ More great Deep Look episodes:
What Gall! The Crazy Cribs of Parasitic Wasps
https://www.youtube.com/watch?v=lOgP5NzcTuA
Why Is The Very Hungry Caterpillar So Dang Hungry?
https://www.youtube.com/watch?v=el_lPd2oFV4
---+ Shoutout!
🏆Congratulations🏆 to the following 5 fans on our Deep Look Community Tab for correctly answering how the adult jumping bean moth escapes the seed… the larva cuts a circular exit door with its mandibles *before* becoming a pupa:
Mr. Fossil
Padmavati Vhanale
Agita
Fabio Franco
Rosy
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