Typical kids who go to elementary school in Japan mostly spend their free time studying, playing baseball, or reading all the manga they can get their hands on. But ten-year-old Joe Nagai from Kobe, Japan, decided to spend his free time raising swallowtail butterflies with his own hands.
Identified by the bright spots that outline their wings, Asian Swallowtails are great pollinators of native plants and flowers.As she looked after them, he noticed a special, heart-warming demeanor. Once released into the wild, the butterflies will stay in the air for a while and then return right back to it. This observation raised a strange question in the boy’s mind: Do his butterflies really remember him?
I’m looking for answers
Joe trained a small group of his larvae to associate the scent of lavender essential oil with the vibrating stimulus.
Determined to find an answer, Joe began searching online for scientific studies that might relate to his question.
The answer came from Dr. Martha Weiss, a renowned entomologist at Georgetown University who had previously studied whether moths can retain memories of their larval days.In a recent Radiolab podcast, Dr. Weiss recounted how the then-second-grader wrote her a detailed, four-page letter. He asked her if she knew the best way to extend her butterfly experience to his own. She replied, pleased by Nagai’s early curiosity.
They soon began scientific extension across continents. A university professor and elementary school students collaborated to adapt complex laboratory methods into a fascinating, child-friendly experiment conducted in Nagai’s home.Shift memoryIn order for a caterpillar to turn into a butterfly, it must undergo a process called metamorphosis. The caterpillar attaches itself inside the cocoon where its body completely collapses and builds itself up again.
This is sometimes referred to as the “viscous phase.”Now, Nagai was asked what memory he would create for his caterpillars going forward when they become butterflies? He designed a smart experience using simple household materials. Starting with a gentle electronic pulse from the muscle therapy device, Joe trained a small group of his larvae to associate the scent of lavender essential oil with the vibrating stimulus.While the swallowtails did not particularly enjoy being near the scent, they were never harmed by it. He left a completely untrained control group. Now that he had a population of caterpillars that didn’t like the smell of lavender, he moved on to the next stage of the experiment. Will their memories of trying to avoid Lavender survive the radical, full-body collapse caused by the transformation?Once the insects appeared as beautiful butterflies, Nagai tested them using a Y-shaped tube maze.
One side had an initial lavender scent while the other side was odor free. The control group of butterflies split evenly and flew into Y’s arms; Meanwhile, the trained butterflies overwhelmingly avoided the scent of lavender! Against all odds, Joe proved that sensory memories can survive the complete reorganization of the body and brain during transformation.
Is memory a generational thing?
He prepared a 33-page research report that shocked the scientific community.
While Nagai could have stopped here, he was interested in knowing whether memory could be transmitted across generations.
After raising his trained butterflies, he tested their offspring and eventually grandchildren. Shockingly, without receiving any vibration training, later generations naturally avoided the smell of lavender. Now, Nagai has revealed definitive evidence of transgenerational inheritance of memory in swallowtail butterflies.“He ran his experiment again, but also tested a second generation, to see if they avoided the same smell they had trained their parents to hate.
A few months later, he wrote to my mother that the results were clear. “His butterflies passed on her memories to her children,” said journalist Annie Rosenthal, Weiss’s daughter.He prepared a 33-page research report that shocked the scientific community. The young man eventually presented his findings at the International Entomological Congress in Kobe, Japan, in 2024. Dr. Weiss also traveled to meet Joe there while briefing global experts, including the Crown Prince of Japan.While butterflies do not consciously teach their children the way humans do, this discovery suggests that life experiences from one generation can influence the next: a phenomenon that scientists are exploring under the lens of epigenetics.Weiss also revealed Nagai’s future on the Signal Hill podcast. “He told me he didn’t actually want to be an entomologist when he grew up. He wanted to be a veterinarian,” she said.