Portuguese 
Tests with Papilio xuthus showed a rejection of lavender among butterflies trained as caterpillars and also among descendants that never received the stimulus. This result led the young researcher to investigate a possible biological transmission of behavior across generations.
Jo Nagai, an 11-year-old student from Kobe, Japan, presented in Kyoto an experiment where swallowtail butterflies maintained an association learned during their caterpillar stage after metamorphosis. Tests also recorded similar behavior among the offspring and grandchildren of the trained insects.
At the 73rd Annual Congress of the Ecological Society of Japan, 70.9% of the butterflies trained avoided the smell of lavender as adults. Among descendants that did not receive the stimulus during the caterpillar stage, the proportion was 64.8% in the offspring and 60% in the grandchildren.
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The control group showed results close to an even split. Among specimens that had not undergone training, 51% avoided lavender, a ratio indicating no clear odor preference.
How the Experiment Tested Memory After Metamorphosis
During the caterpillar phase, the animals were exposed to the smell of lavender along with an unpleasant stimulus, so that the aroma became associated with a negative experience. After metamorphosis, the adult butterflies were placed in Y-shaped equipment to choose between two paths.
One side offered sugar water, while the other combined the same reward with the smell of lavender. The increased frequency of choices for the path without the aroma among trained animals allowed observation of whether the association formed before metamorphosis remained in the adult stage.
The result does not imply that the butterfly retains a conscious memory comparable to human memory. The experiment records the persistence of a learned behavioral response before the animal’s transformation, a process in which the organism and the nervous system undergo significant reorganization.
Jo expanded his inquiry by testing subsequent generations. Offspring and grandchildren of the trained butterflies did not receive the aversive stimulus as caterpillars, yet still exhibited rejection rates of lavender higher than recorded in the control group.
The numbers decreased with each generation: 70.9% among the originally trained individuals, 64.8% among the offspring, and 60% among the grandchildren. The summary presented at the congress suggests epigenetic mechanisms as a possible explanation for this pattern, rather than an established conclusion.
Epigenetics involves changes that can alter gene activity without necessarily modifying the DNA sequence. Applied to the experiment, this hypothesis suggests that the experience of the initial generation may have left biological effects influencing their descendants, rather than them inheriting a conscious memory from their ancestors.
A Childhood Question Led to Scientific Collaboration
The research began with an observation made by Jo while still in elementary school. He was raising butterflies at home and noticed that some continued to fly near him even after being released, prompting his curiosity about memory after metamorphosis.
“I always thought my butterflies might remember me even after metamorphosis,” the boy wrote to entomologist Martha Weiss, a professor at Georgetown University in the United States, seeking help to turn his question into an experiment.
Georgetown University documents the collaboration between the two and reports that Jo reached out to the researcher after finding a paper on memory retention in moths following metamorphosis.
In 2022, when Jo was 8 years old, he sent a four-page letter to Weiss asking whether the phenomenon could also occur in the butterflies he was raising. This communication evolved into a collaboration to plan, execute, and analyze experiments related to insect memory and the potential transmission of the effect.
Part of the initial tests was conducted at the boy’s home, using lavender oil and a small muscle therapy device among the materials adapted for the experiment. The logic was to associate a scent with an unpleasant experience during the larval stage and observe the animal’s reaction after metamorphosis.
In 2024, Jo presented part of the research at the International Congress of Entomology, where he met Weiss in person. The next phase shifted from observing the retention of the association in a single individual to tracking whether any effects would also appear in descendants that had never been trained.
This expansion was presented at the Japan Ecosystem Society conference in March of this year. The official record identifies Jo as a student at Ibuki Higashi Elementary School and describes the work as an investigation into the intergenerational transmission of memories formed during the larval stage of Papilio xuthus.
The percentages presented support a behavioral pattern among the observed generations, but the mechanism responsible for it has yet to be demonstrated. The epigenetic hypothesis needs further investigation, and broader conclusions depend on independent studies and peer-reviewed scientific publication.
