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, and probably everyone has marveled at their erratic movements, or heard a fabulous tale about them. 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 the rugged Cape region of Baja California.

The common jumping beans sold in novelty shops throughout the southwestern United States come from a deciduous shrub (Sebastiana pavoniana) with dark green, leathery leaves that turn red during the winter months. The jumping bean shrubs grow on rocky desert slopes and along arroyos in the region of the Rio Mayo in the states of Sonora and Chihuahua. 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." Mr. WOLFFIA (the editor of WAYNE'S WORD) recently photographed this interesting shrub in canyons of the Sierra de la Laguna in the Cape region of Baja California. By late winter the shrubs become a blaze of red, in sharp contrast with the beautiful green fan palms (Brahea brandegeei).

Another lesser-known jumping bean shrub (Sebastiana bilocularis) is sometimes called the Arizona jumping bean, although it is by no means limited to Arizona. Its former name was Sapium biloculare; however, according to The International Plant Names Index (IPNI), its accepted name is now Sebastiana bilocularis. The Arizona jumping bean occurs along washes and rocky slopes from the vicinity of Ajo, Arizona, south through the desert areas of Sonora, Mexico and Baja California. It also occurs on some of the islands in the Gulf of California. Like many other members of the diverse Euphorbia Family (Euphorbiaceae), freshly cut stems of both species of jumping bean shrubs exude a poisonous milky sap. In fact, several tribes of native Americans reportedly used the sap to poison their arrow tips. In Mexico the shrubs are sometimes called "yerba de la flecha," which translated means herb of the arrow.

Probably the most interesting thing about Mexican jumping bean shrubs are the remarkable "beans" that jerk and roll about with seemingly perpetual motion. It is doubtful (or very rare) that they actually "jump" above the surface of the ground, but they can certainly roll and tumble along in different directions. Just as pineapples are not apples and peanuts are not nuts, the jumping bean is not a bean, nor is it a seed. It is actually a small, thin-shelled section of a seed capsule containing the larva of a small gray moth called the jumping bean moth (Laspeyresia saltitans). 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. It is these separate sections (technically called carpels) that are sold as "jumping beans."

The jumping bean moth belongs to the Olethreutidae, a large family of moths, some of which are serious agricultural pests. Like the jumping bean moth, the larvae bore into the fruits and feed on the tissue inside; however, unlike the jumping bean moth, they attack fruits that we humans also like to eat. Some of the jumping bean moth's destructive relatives are the codling moth (a serious pest of apples), the oriental fruit moth (a serious pest of peaches), the black-headed fireworm (a serious pest of cranberries), the grape berry moth, the pea moth, the cypress cone moth, and the strawberry leaf roller. In fact, the codling moth is one of the world's most destructive insects, causing millions of dollars annually in apple losses and moth control expenses. Luckily, the jumping bean moth only likes jumping bean seeds and is of no economic importance as an agricultural pest. They will not be confiscated by the U.S. Border Patrol or the U.S. Agricultural Inspection Agency.

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 (ovaries) of female flowers. When the eggs hatch, the tiny, immature larvae bore into the young capsules and begin feeding on the developing seeds inside. [Some references suggest that the eggs are deposited inside the capsules, but C.L. Hogue (Natural History Museum of Los Angeles County Science Series 27, 1974) states that the larvae eat their way into the soft green capsules.] Only seeds without larvae will reach maturity and be viable, and luckily for the plant, not all capsules are infested with moth larvae.

Although the thin-shelled jumping bean capsule containing its moth larva superficially resembles the life cycle of some insect galls, it is NOT A GALL. Galls are usually produced by the plant in response to a chemical or mechanical irritation (stimulus) caused by ravenous insect larvae deeply embedded in the plant's tissue. The swollen (tumorous) tissue provides food and a brooding chamber for the larvae, and is usually found in stems or leaves. The papery jumping bean capsules are not galls, they are genetically-programmed structures that are formed with or without the presence of the moth larva. The larva is clearly a seed predator that is simply taking advantage of the tasty seed inside the capsule.

The WAYNE'S WORD staff did some investigating, and sure enough, there is a "jumping gall" that behaves very much like a Mexican jumping bean. This amazing story is discussed in an article by F.A. Leach (Natural History Vol. 23, 1923). The minute, globose galls are only 1 mm in diameter. They are attached to the leaves of several native oaks in California's Sacramento Valley. Each gall is inhabited by a tiny cynipid gall wasp appropriately named the "jumping oak gall wasp" (Neuroterus saltatorius). When the minute galls fall to the ground they begin hopping about like fleas. According to F.A. Leach, they can jump over one centimeter vertically and twice as far horizontally. Like jumping beans, the larva inside is active during the summer months, but ceases its activity later in the fall when it changes into a pupa. The gall topic is a favorite one at WAYNE'S WORD and the subject of future articles.

By late summer, capsules of the Mexican jumping bean shrub have separated into three sections, each section splitting open and ejecting its seed. Hollowed out sections (carpels) containing moth larvae fall to the ground and start a new career of jumping and hopping. According to Carlton Heckrotte (Journal of Thermal Biology Vol. 8, 1983), the jumping behavior is clearly influenced by temperature. Perhaps this is a way to move the capsules out of the hot sun to a more concealed location, such as into a crevice or under a rock, prior to the final critical stages of metamorphosis during which the adult moth is formed. However, the larvae also exhibit their peculiar jerking behavior in the shade, suggesting that other genetic or physiological factors may be involved.

It is interesting to speculate about the energy required to move a Mexican jumping bean that weighs about as much as the moth larva (approximately 0.08 gram). If the larva were turning free inside the capsule section or carpel it would seem almost impossible for it to move the carpel with such force that it actually rolls. To accomplish this feat the larva spins a silk lining on the inner walls of the carpel. This thin, inconspicuous lining may not be visible at first, but soon covers the inside of the carpel. Like other moth larvae, silk threads are secreted from modified salivary glands in the mouth region. By grasping the silken lining with its forelegs and snapping its body, the larva is able to transfer the full force of its movement to the carpel. [According to F.S. Truxal (Los Angeles County Museum Quarterly Vol. 3, 1964), the larva grasps the silken lining with its abdominal prolegs, draws back its head and forebody, and strikes the wall of the carpel with its head.] Because of the eccentric, convex shape of the carpels, they will tumble and roll about on a level surface. It is doubtful (or very rare) that they actually "jump" above the surface. As winter approaches the larva spins a silken cocoon around itself. Old carpels are often filled with larval castings and a silken cocoon. Jumping beans will remain motionless during the winter months as the larva transforms into a pupa, and eventually into an adult moth. Larvae and pupae contained within their papery carpel containers are the vital connecting links with the next season's crop of capsules.

The following spring or summer, when jumping bean shrubs are once again in flower, the pupa pushes through a small circular door in the wall of the carpel, the pupal covering splits open, and a small gray moth crawls out of the pupal case. Like other dioecious species, with separate male and female individuals in the population, the moths come in 2 sexual forms: egg-bearing females and sperm-bearing males. In fact, the primary role of the adult moths is to find a mate and pass on their genetic information (DNA) to future generations. Soon after mating, the female moth lays her eggs on the new crop of immature capsules and the amazing life cycle is renewed. The fascinating relationship does not appear to be mutually beneficial to the shrub since pollination is not dependent on the moth and the larva is clearly a seed predator.

The construction of the exit door, often so uniformly circular that it could have been made by an electric drill, is truly fascinating. Without any cutting mouthparts how could the exit hole have been made by the adult moth? Actually, the circular escape hatch was cut the previous year by the larva, shortly after it ceased its jerking movements and before it changed into a pupa. The door is conveniently placed directly opposite one end of the cocoon. It is only partially cut through the wall of the capsule, and is easily pushed open by the emerging moth. This is sort of like pushing a small circular piece out of a scored stencil. The cutting of the exit door is remarkable when you consider that the larva has no knowledge of the purpose it will eventually serve.

Another fate remains for jumping bean capsules that harbor the moth larvae, particularly if they happen to be in the vicinity of Alamos, Mexico. This is the land of the jumping bean and the home of Senor Joaquin Hernandez, the legendary "king of the jumping beans." When he was only twelve years old, Joaquin saw the potential for marketing jumping beans and started a thriving industry that has persisted for more than 60 years. People from the community are paid for all the beans they can deliver to Joaquin's business in Alamos. During favorable seasons, Joaquin employs 50 people for selecting and packing the beans, and in some years he exports 20 million beans.

Jumping beans will continue their movements and vibrations 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 stimulates them into greater activity. In time their saltations 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.

Mexican jumping beans are now available from late July to late April. Their normal adult summer cycle has been extended by placing them in temperature controlled coolers. They are sold in small plastic boxes and in larger containers. Go to the following URL for more information and to order Mexican jumping beans:

www.jumping-beans.com

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