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 Insectlorepedia > Insects > Jumping Bean Moth |
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Mexican Jumping Beans are found in the Rio Mayo region of Mexico, in the states of Sonora and Chihuahua, where a particular shrub of the Spurge family, known as Sebastiana Pavoniana grows. The Mexicans call the plant "Yerba de la Flecha", which means "plant of the arrow", originating from ancient times when they put the milky sap on their arrow tips. During a critical few days of the year following the seasonal rains, the shrub flowers. The small, blue Jumping Bean Moth visits the flowers and lays its eggs on the seedpods. When the eggs hatch, the tiny hungry larvae (baby caterpillars) hastily burrow their way into the developing seedpods. As the seedpods ripen, they develop a characteristic 3-sided shape, with the larvae continuing to feast safe inside until only the hard woody shell remains. When the seedpods are mature, they fall to the ground and break into 3 beans, one of which may be home to the strange visitor sealed inside. Having eaten most of the inside of the bean, the larva lines the inside of the bean with silk to make itself comfortable. It then attaches its back legs to the silken wall. To make the bean jump, the larva curls up and then rapidly springs uncurled again, jerking the bean forward. Exactly why the larva should expend so much energy making the bean jump, sometimes for almost a year, remains one of nature’s mysteries. Where the beans fall is liable to be hot and sunny, and they might be fried in the sun, trodden on, or eaten by an animal eager for a tasty meat-filled bean snack. The most likely explanation seems that by jumping, the bean will move itself into a safe place where the larva can relax, pupate and undergo the miracle of metamorphosis ready to continue the life cycle. Although the beans do jump most when they are warm or in light, fresh ones often jump vigorously even when they are not especially warm, so maybe the movement is also a way to spread the creature's "gene pool". Rapid movement or knocking will surprise them and they usually "play dead" for a while, presumably to evade predators, although knocking against each other doesn't seem to have the same effect – Do they somehow know that their friends are nearby ? Each bean usually continues to jump for many months until it finds a place where it remains cool and dark. Typically, "pet" beans will jump well for many months after they have been gathered, although with great care they can keep going for almost a year, but they do gradually get more "tired". The creature has a natural "calendar" which helps it to get the timing right so that the lifecycle carries on at the right time each year. This "calendar" senses the natural change of light and dark, warm and cold as the days and seasons pass. When the Ecdysone hormone starts to signal the larva's body to change, it nibbles a tiny, perfectly circular "trapdoor" in the bean, spins a silk cocoon around itself, and settles down as a pupa (or "cocoon") for a well-earned rest. The little trapdoor usually remains attached by one small part to keep the occupant private until it is ready to leave. (It's just as well that it instinctively knows to prepare the trapdoor, because as a moth it doesn't have to ability to cut it. If the larva forgot to make the trapdoor, it would have a nasty surprise when it had turned into a moth and found itself trapped inside the bean !) Over the next few weeks, metamorphosis takes place and the bean remains apparently quite inert until it senses that the seasonal rainfall has returned, usually in June. After 20 or 21 days, the moth pushes the trapdoor open and emerges - miraculously at exactly at the right time to catch the Sebastiana Pavoniana shrub flowering! The little moth sits and stretches its wings in the sun for a while, then flies off. It now has only a very few days of life remaining to mate, find a shrub and lay its eggs to complete the lifecycle. Beans which have stopped jumping because they have been left cold and dark may wait many months until the critical day arrives to catch the exact timing of the rains, and synchronise their emergence with the flowering of Sebastiana Pavoniana. |
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