A Mexican jumping bean
is a phenomenon native to Mexico
(where it is known as a brincador
, or "hopper"). Physically, Mexican jumping beans resemble small tan to brown beans. They are a type of seed
in which the egg of a small moth
has been laid. It is the moth's larva
which makes them 'jump'. The beans themselves are from a shrub
of the genus Sebastiania
or S. pavoniana
), itself often referred to as the jumping bean
, while the moth is a member of the genus Cydia
called a jumping bean moth
After the egg has hatched, the larva eats away the inside of the bean, making a hollow for itself. It attaches itself to the bean with many silk threads.
The larva may live for years inside the bean with varying periods of dormancy. If the larva has adequate conditions such as moisture, it will live long enough to go into a pupal stage. Normally in the spring, the moth will force its way out of the bean through a round "trap door", leaving behind the pupal casing. The small, silver and gray-colored moth will live for only a few days.
The beans jump as a survival measure in order to protect the larvae from the heat, which can cause them to dry out. The ultraviolet rays from the sun stimulate them to jump, even in cool temperatures, but leaving them in the sun for extended periods will dehydrate and kill them.
Playing with/testing the beans
When the bean is abruptly warmed, for instance by being held in the palm of the hand, the larva twitches and spasms, pulling on the threads and causing the characteristic hop. "Jump" is often an exaggeration, but the beans do noticeably move around.
The beans should become active if you hold them in your hand (out of the box) for a few minutes. The beans should also appear to be a very slight shade of green on the side (as shown in the bean in the top picture, on the right). If the bean starts to turn brown (top picture, bean on the left), that indicates it is dying. If you pick up a bean and hold it to your ear and hear a rattle inside, the larva inside has died.
"Watering" and storage of the beans
To replenish the beans due to dehydration, they need to be soaked for a 4 to 5 hour period in dechlorinated (e.g., bottled) water once or twice a month. Chlorinated tap water will kill them. Spraying the beans with a little water is ineffective in maintaining their lifespan. Alternatively, you may let tap water stand in an uncovered glass for about six hours before using in order to let the chlorine dissipate out. Beans should be stored in a cool dry place. Freezing will kill them.
Source of the beans
The Mexican Jumping Bean (Laspeyresia Saltitans) comes from the mountains in the states
of Sonora Sinaloa
; indeed, Álamos, Sonora
, claims to be "the jumping bean capital of the world". They can be found in an area approximately 30 by 100 miles wide where the host tree (Sebastiana Pavoniana) grows. During the Spring, moths emerge from last year's beans and deposit their eggs on the flower of the host tree.
Did You Know. . .
Jumping beans were used as a recurring gag in many cartoons
in the 1930s to the 1950s, whereas a character who "ate" the beans simply makes his/her whole body bounce out of control and lands into something painful.
They are still widely available for sale in the USA. (see links below) In the UK they were a common novelty item in the 1970s. They are a popular scientific and classroom project even now.
A plastic toy under this name was manufactured and sold in packages containing several in the 1960s. It resembled a "time pill" capsule and had a metal ball inside. When the surface the capsule was laid on was tilted, the ball would roll to the other end and twitch the capsule.