The vast southwest desert region of North America contains many fascinating wild plants, but none are more intriguing than the Mexican jumping bean. Jumping beans are commonly sold in novelty shops and by street vendors on both sides of the border.   In the regions where they grow wild, they are often collected by children and sold to local dealers who export them to the United States. The actual jumping "bean" is not a bean at all.  It is produced by a native shrub or small tree that grows wild in the deserts of mainland Mexico and in Baja California.

The common jumping beans come from a small shrub with dark green, leathery leaves that turn red during the winter months. The jumping bean shrubs grow on rocky desert slopes of the Sonoran and Chihuahuan deserts. One of the best places to see this shrub is in the vicinity of Alamos, Mexico, known locally as the "jumping bean capital of the world."

Jumping bean shrubs typically bloom during the spring and summer months, and this is when the female moth lays her eggs on the green immature capsules of the flowers. When the eggs hatch, the tiny, immature larvae bore into the young capsules and begin feeding on the developing seeds inside. The larvae eat their way into the soft green capsules.

The bean is actually a small, thin-shelled section of a seed capsule containing the larva of a small gray moth called the jumping bean moth. After consuming the seed within the capsule section, the robust, yellowish-white larva has the peculiar habit of throwing itself forcibly from one wall to the other, thereby causing the jumping movements of the capsule. Mexican jumping bean capsules typically separate into three parts or sections, some of which contain a moth larva. These are sold as "jumping beans."

Hollowed out sections (carpels) containing moth larvae fall to the ground and start a new career of jumping and hopping. The jumping behavior is clearly influenced by temperature. Perhaps this is a way to move the capsules out of the hot sun to a area of shade, such as into a crevice or under a rock. The larvae eventually goes through its stages of metamorphosis during which the adult moth is formed. During June, the ground beneath large jumping bean shrubs is littered larva-bearing "beans". The jumping beans sound like the patter of rain drops on dry leaves.

Jumping beans will continue their movements and jumping for weeks or months when placed in a container where they can get air (a shoe box is adequate). Placing them on a warm object or in your hand generally makes them have greater activity. In time their jumping will cease as the larvae undergo metamorphosis. Up to six months later, often after you have completely forgotten about them, adult moths will emerge from the beans.
Unless you happen to have jumping bean shrubs growing in your garden, the marvelous life cycle will be terminated as the moths finally die.

Excellent site for further research is http://daphne.palomar.edu/wayne/plaug97.htm