What makes Mexican jumping beans jump?

Have you ever wondered about the secret behind the lively leaps of Mexican jumping beans?

Sold as popular souvenirs along bustling boardwalks, these seemingly animate objects are actually seeds that host the larvae of a small moth species.

The beans “jump” when the larvae stir within, knocking against the seed wall. But could there be more to this intriguing phenomenon beyond just random movement?

Recently, an in-depth study by researchers at Binghamton University has revealed some surprisingly complex behavior within this fascinating microcosm.

Jumping beans react to the light

Lindsey Swierk, an assistant research professor of biological sciences, was intrigued to find out how these larvae respond to their surroundings.

The landscapes where the seeds fall can vary dramatically, from sun-drenched plains to shadowy groves. This prompted Swierk and her students to investigate how the larvae inside the jumping beans react to varying light conditions.

The researchers found that these larvae are capable of registering different light colors, asserting more vigorous jumping actions under specific hues.

Jumping to escape the heat

“When a seed drops to the ground from shrubs, the moth larva inside is at the mercy of whatever environmental temperature the seed experiences,” said Swierk.

“The ground could be scorching hot in direct sunlight. A little moth larva inside of a seed like this can only withstand so much heat – and so they jump away.”

Interestingly, the bean acts as an “extended architecture” for the larvae – a naturally occurring structure that the organism utilizes without constructing itself.

Much like a hermit crab finds refuge in a borrowed shell, the Mexican jumping bean becomes the adopted home for the larva, offering both shelter and a means of responding to the environment.

How light influences survival

To explore this intriguing relationship further, Swierk and her team designed experiments to understand how different light colors influence the behavior of these seed-bound caterpillars.

Contrary to expectations, the researchers discovered that light penetrates the seed wall only minimally – less than one percent -suggesting that the larvae rely on incredibly faint cues to sense their surroundings.

Despite this, the larvae respond differently to different light spectra, moving the most under red light and the least under purple light.

“Somehow larvae are picking up on these differences. Whether that’s because of very minute temperature changes or because of extremely sensitive photoreceptors, we’re not sure yet,” noted Swierk.

“But they’re using light somehow as a cue to change their behavior, which probably has to do with the fact that these different lighting spectra are correlated with different environmental conditions.”

Jumping beans under environmental stress

Continuing their line of investigation into the impact of environmental factors on these larvae, Swierk and her students uncovered an intriguing dilemma.

The researchers found that larvae possess the ability to repair their host seeds using silk threads, but this might compromise their heat evasion abilities.

The experiments revealed that when seed walls were damaged, the larvae’s ability to respond to high heat by jumping decreased. This suggests that the disruption caused by the damage could disconnect the internal silk threads that enable the larva’s movement.

Swierk noted that these animals are extremely sensitive to temperature. “A common story here is that we see these larvae using very nuanced cues to change their behavior in response to heat, and we’re also seeing that additional stressors like predation attempts can impair their ability to appropriately respond to temperature.”

Climate change and insect behavior

The research does more than shed light on the remarkable world of Mexican jumping beans. The findings have broader implications for our understanding of insect behavior in the era of climate change.

“Responding to temperature change is a big deal. As the climate changes, we need to learn how animals detect imminent thermal stress and what limits their adaptive responses,” said Swierk.

“What we learn about Mexican jumping bean larvae might help us better understand how other insects with limited movement cope with heat stress in their environments.”

The study is published in the journal Behavioural Processes.

—–

Like what you read? Subscribe to our newsletter for engaging articles, exclusive content, and the latest updates. 

Check us out on EarthSnap, a free app brought to you by Eric Ralls and Earth.com.

—–