Boy Discovers Swallowtail Butterflies Remember Caterpillar Life And Pass Those Memories To Their Offspring

When 10-year-old Jo Nagai was raising swallowtail butterflies at his home in Kobe, Japan, he noticed something curious.

The butterflies he had cared for as caterpillars seemed to recognize him. Wild butterflies flew away, but his stayed close.

Most children might have simply smiled and moved on. Instead, the second-grader decided to investigate.

Jo wrote a four-page letter to Dr. Martha Weiss, an entomologist at Georgetown University whose research had explored whether moths could retain memories through metamorphosis. He asked if she would help him design a similar experiment for butterflies. She agreed.

Working from home, Jo trained swallowtail caterpillars to associate the scent of lavender with a mild vibration produced by a muscle therapy device. After the caterpillars underwent metamorphosis and emerged as butterflies, he tested whether they still reacted to the scent.

Despite one of nature’s most dramatic transformations—where a caterpillar’s body is largely broken down and rebuilt inside a chrysalis—about 70 percent of the butterflies still avoided the lavender.

The learned response had survived metamorphosis. Then Jo took the experiment a step further. He bred the butterflies and tested their offspring, which had never been exposed to the vibration. According to the results he shared with Dr. Weiss, they also avoided the lavender. The same response was observed in the next generation as well, suggesting that the learned aversion may have been passed from one generation to the next.

While butterflies aren’t consciously teaching their young the way humans do, the findings point to the possibility that experiences from one generation can influence the next—a phenomenon scientists continue to explore through the field of epigenetics.

Jo documented his work in a 33-page research paper and presented his findings at the International Congress of Entomology in Kobe in 2024 to surprised scientists.

What began with one curious observation became a remarkable scientific journey, reminding us that curiosity, careful observation, and a willingness to ask questions can sometimes lead to extraordinary discoveries.