10-year-old Japanese boy finds butterflies he raised from caterpillars remember him; his curiosity leads to a surprising discovery about how insect memory works

10-year-old Jo Nagai from Kobe, Japan noticed something unusual about the swallowtail butterflies he had raised from caterpillars. Each time he released them into the wild, they would linger briefly and then fly back to him. That observation led to a home experiment, a cross-continental collaboration with a Georgetown University scientist, and eventually a 33-page research report that surprised the scientific community.

Jo Nagai Butterfly Experiment

Nagai had been hand-raising Asian swallowtail butterflies as a hobby. The repeated behaviour of his released butterflies returning to him prompted a question he could not let go of: did they actually remember him?


He went looking for existing scientific research and found the work of Dr Martha Weiss, an entomologist at Georgetown University who had previously studied whether moths could retain memories from their caterpillar stage. As a second-grader, Nagai wrote her a detailed four-page letter asking whether her moth experiment could be adapted to butterflies. Weiss wrote back.

The story of their collaboration was first recounted by Dr Weiss on a recent episode of Radiolab, the science podcast. Annie Rosenthal, a journalist and the daughter of Dr Weiss, also reported on the findings separately.

What followed was a collaboration between an elementary school student in Japan and a university professor in the United States, working together to adapt laboratory methods into an experiment Nagai could conduct at home.

Butterfly Memory and Metamorphosis

The central scientific question was whether a memory formed during the caterpillar stage could survive metamorphosis, the process by which a caterpillar seals itself inside a chrysalis, breaks down almost entirely into biological matter, and rebuilds itself as a butterfly.

Nagai designed a training experiment using a mild electronic pulse from a muscle therapy device and aromatic lavender oil. He conditioned a group of caterpillars to associate the lavender scent with the vibrating stimulus, causing them to avoid it. A separate control group received no training.

Once both groups completed metamorphosis and emerged as butterflies, he tested them using a Y-shaped tube maze. One arm contained the lavender scent, the other was scent-free. The control group split evenly between the two arms. The trained butterflies overwhelmingly avoided the lavender side, indicating the aversion formed during the caterpillar stage had carried over.

Transgenerational Memory in Insects

Nagai did not stop there. He bred his trained butterflies and tested their offspring, and then the generation after that.

Neither the second nor third generation had received any vibration training. Yet both consistently avoided the lavender scent without any conditioning.

"He did his experiment again, but tested a second generation too, to see if they avoided the same smell he'd trained their parents to hate. And a few months later, he wrote to my mom that the results were clear. His butterflies had passed their memories on to their children," said Annie Rosenthal, recounting the findings.

The results pointed to what researchers describe as transgenerational memory inheritance, the passing of learned behavioural responses to offspring who never experienced the original stimulus. Dr Weiss discussed Nagai's future plans on the Signal Hill podcast, where she revealed he told her he does not want to become an entomologist when he grows up. He wants to be a veterinarian.

This finding connects to the broader scientific field of epigenetics, which examines how life experiences in one generation can shape the behaviour and biology of the next without changes to the underlying genetic code.

Insect Memory Science

Nagai's findings built on earlier laboratory research. A study published in PLOS titled Retention of Memory through Metamorphosis: Can a Moth Remember What It Learned As a Caterpillar? had previously shown that caterpillars conditioned to avoid a chemical smell, the kind used in nail polish remover, through mild electric shocks continued to avoid it after transforming into adult moths.

That study, reported extensively in science media including Times of India, suggested certain neurons survive the metamorphic process intact, carrying information across life stages. Scientists had long assumed metamorphosis represented a near-complete biological reset. The emerging body of research indicates that at least some brain structures and the memories associated with them persist through the transformation.

Researchers have also noted that female butterflies tend to lay their eggs on the same plant species they consumed as caterpillars, a pattern some scientists believe may reflect memory continuing to influence adult behaviour.

Jo Nagai Research and Recognition

Nagai compiled his findings into a 33-page research report. In 2024, he presented them at the International Congress of Entomology held in Kobe, Japan. Dr Weiss flew out to attend, and the audience included global experts and the Crown Prince of Japan.

Despite the scale of what his curiosity produced, Nagai told Dr Weiss he does not plan to become an entomologist. He wants to be a veterinarian.