We were at a party, when eight-year-old Heather fetched her pet. It was held in a small, thin gift box that vibrated gently and moved slightly. She allowed each of us to guess her pet. All twelve of us failed. But in the process, we discovered the fascinating life history of a creature, often called simply as the Mexican jumping bean.
But before we do that, let us remember the vagaries of names. 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).
Sapium biloculare and Sebatiana pavoniana, or the jumping bean shrub belongs to family Euphorbiaceae.
It flowers in spring and summer months. A female moth lays her eggs on the ovaries of female flowers. When the eggs hatch, the tiny, immature larvae bore into the young capsules and begin feeding on the seeds developing inside. Only seeds without larvae will reach maturity and be viable, and luckily for the plant, not all capsules are infested with moth larvae. When the larva is exposed to sunlight or warmth, it jumps! During winter, the larva will remain motionless and transform into a pupa. By spring, they become adult moth and are ready to begin the life cycle again.
Why does the larva jump when exposed to sun? Scientists believe it a defense mechanism that helps the larvae survive in the wild. The larva moves 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. Because of the convex shape of the capsule, the larva will move extraordinarily long distances on a plain surface.
Seed capsules separate into three parts or sections, some of which contain a moth larva. It is these separate sections (carpels) that are sold as "jumping beans." Mexican Jumping Beans are seasonally harvested once a year. They are easy to maintain, require no food, needing minimal care. They can be stored in shoeboxes, from where, about six months later the adult moths emerge. In order for the life cycle to continue, they need the food plant. Although fascinating, this relationship between the moth and the plant is not beneficial for the plant. The moth is not the pollinator of the shrub, and the larva is clearly a seed predator.
My dog has become attached to the jumping beans. She thinks they are her babies. She takes care of them and watches them while we hold them. She sleeps along with them. What if they die I am not sure what to do?