The colorful “beans” sold at novelty shops on both sides of the border are not beans at all; rather they’re seed pods from Sebastiania pavoniana shrubs native to Mexico, which more closely resemble spurges than legumes.
Each tan to brown pod houses a moth larva attempting to survive the scorching Sonoran Desert sun by hopping between pods in search of shade.
Origins
“Jumping beans” sold at novelty stores are actually seed pods from a shrub native to Mexico, belonging to the Euphorbiaceae spurge family. Sebastiania pavoniana can be found growing along rocky desert slopes and along arroyos throughout Sonora and Chihuahua states in springtime; moths lay their eggs on these immature green pods before hatching eggs that bore into them and began eating from within them.
Critters use their movement to spread pods as they wriggle inside them. This wiggle causes beans to jump as a natural way of dispersing pods; additionally, these movements protect from hot sun and wind.
Once they become warm, however, their pods begin to wiggle more vigorously and leap. If left exposed in such conditions for too long, however, their inhabitants could perish.
In an intriguing Deep Look episode, Wayne’s WORD team carefully observed Sebastiania pavoniana pods found in the Sonoran Desert and kept their moving seeds due to tiny larvae living inside. As these larvae curl and have spasms, which causes pods to bounce around rapidly – this likely serves as an adaptation to sunlight or intense heat that would otherwise kill off their development into pupae.
Once a caterpillar reaches its pupal stage, it cuts a partial opening at one end of its pod and creates a space that eventually splits open to release a tiny moth that lives for only a short while before depositing its eggs into newly developing seed pods – thus continuing the annual cycle.
Habitat
Mexican Jumping Beans provide an engaging form of natural entertainment. These intriguing seed pods, colonized by moth larvae, jump when exposed to heat stimulation. Sold worldwide as novelty items and providing insight into plant/insect relationships.
Tortricidae family moths, commonly referred to as jumping bean moths, are responsible for creating this unusual effect. By living inside certain species’ seeds and creating enough heat sources (sun or palm of hand), they cause these seeds to move and “jump.” Sometimes, their movements resemble more of a rocking motion than actual jumping, and they may not always do it in precisely the same way each time.
Once moth larvae have set up their homes in seeds, they use saliva to seal off their pods with them and eventually fall to the ground, ripening and then falling open, releasing seeds for feeding; within days, moths will consume these seeds before finally succumbing to death themselves.
When seed pods are collected before their seeds ripen, they remain active for months as they await moth generation to arrive. Alamos in Sonora is considered the Jumping Bean Capital of the World, where locals collect these seed pods to sell as novelty items or keep alive for up to five months by misting them weekly with water, misting them regularly with misting devices.
Pods
Mexican jumping beans wriggle and shift anxiously when held, creating an illusion that they may be insects or toys if you happen to catch one in your hand. But in truth, both might exist! If you do manage to see one for yourself, they might provide hours of fun playback!
As known by its scientific name Sebastiania pavonia), this shrub found throughout northern Mexico and the southwestern United States has seed pods known as “yerba de flecha,” or beans, that contain moth larvae living inside. Adult moths lay their eggs on this flowering plant’s flowers before its seed pods drop from its ferns in late summer, with each one containing an individually hollowed-out seed; after that, moth larvae begin chewing their way in for sustenance.
Jumping beans move due to an irregular spasm of the larva, which hits against its seed in the pod and makes it move. Theories on why they move this way vary; most agree it’s trying to find some shade from direct sunlight – otherwise, the moth would quickly overheat and die if left in direct sunlight alone! Their seemingly random movements actually help them find shade faster.
McKee and Tabatabai put their beans through rigorous tests, recording 37 moving beans on a flat surface covered with aluminum foil to dissipate heat evenly. After recording their movements, McKee and Tabatabai used computer simulation to analyze each path taken by each bean, ultimately finding that, given enough time and the right direction, jumping beans always reached shade areas; however, directed walks could prove hazardous; choosing an improper path could cause it never reaching shade at all and lead to its death.
Larvae
These peculiar “beans” are actually seed pods from Sebastiania pavoniana shrubs found clinging to dry slopes in Sonora and Chihuahua in Mexico, where Laspeyresia saltitans moth larvae lay their eggs in each pod and devour its seeds – giving each bean the appearance of being “jumping.”
Moth larvae lead a dismal existence within a jumping bean pod. Caged within its rigid walls and the hard seeds it consumes, it lives an uncomfortable reality in near darkness. Too much direct sunlight could dry out its larva and kill it; to avoid this fateful outcome, its existence requires it to jump about trying to find some shade somewhere within its pod.
There are various theories behind the phenomena of jumping bean pods, with most agreeing on its cause being larval spasms that cause them to hit against seed pod walls repeatedly, thus making the bean appear to move back and forth between sides of its pod. Many also speculate that their movements are motivated by the larvae’s desire for cooler temperatures, whether that means on the ground where pods land or being held close in someone’s warm palm.
So next time you see a jumping bean shimmying across your path, take pity on its little moth inside and nudge it towards some shade – after all, it is just trying to survive, and that is the beauty of evolution – even when trapped within its seed pod, these moths have learned how to adapt effectively despite difficult circumstances.
Movement
Northern Mexico and the Southwest feature many plants with pods known for their extraordinary movements, most famously “jumping beans.” You may have seen these distinctive pods sold at novelty shops or street vendors on both sides of the border – but what are they, and why do they bounce around so quickly? Jumping beans are seed pods from a shrub called Sebastiania pavoniana with moth larvae inside that cause them to jump.
Cydia sal titans moth larvae enter immature seed capsules and begin munching them, hitting against their walls while doing so, giving an illusion that these moths are “jumping.”
Seed pods mature by opening and expelling their contents, including larvae. Hollowed-out sections of pods containing moth larvae fall to the ground and begin their journey as jumping and hopping moth larvae, although more like rocking than jumping motion. Temperature seems to influence their movements, with intensified activity occurring as temperatures increase – potentially an effort by these capsules to move out of direct sunlight, into crevices, or under rocks where it will remain more relaxed, where they can undergo metamorphosis into adult moths.
Jumping beans have long been known to move and vibrate on warm surfaces like the palm of a hand for weeks or even months until their moth inhabitants complete metamorphosis into adults, at which point they stop shaking altogether. Wayne’s Word has found similar phenomena occurring within a minute: globose galls attached to California native oak leaves – called “jumping galls” by their infesting cynipid gall wasps – behaving similarly to jumping beans.
