When a caterpillar turns into a butterfly, the transformation is so radical that it's hard to believe they belong to the same species.

But regardless of the new wings and body, the new diet and airborne lifestyle, butterflies remember what they learned as babies.

In a study published yesterday in Public Library of Science ONE,

Georgetown University biologists gave mild shocks to tobacco hornworm caterpillars while exposing the caterpillars to particular odors.

After the hornworms built cocoons and emerged as moths – a process that involves the reorganization of both brain and nervous system – they still avoided the smells that once brought them shocks.

The findings "challenge a broadly-held popular view of lepidopteran metamorphosis: that the caterpillar is essentially broken down entirely, and its components reorganized into a butterfly or moth,"

wrote the researchers.

Led by evolutionary ecologist Martha Weiss, they suspected that larval memories, if maintained at all, would be stored in the so-called mushroom bodies – areas of the brain that receive information directly from the antennae.

Since mushroom body neurons that accumulate early in larval development are lost during metamorphosis, the hypothesis was easy to test: the researchers conditioned the caterpillars at different ages.

As they predicted, caterpillars that learned late to associate shock and odor kept the memory into adulthood. Those who made the association early emerged from their cocoons without remembering.

Beyond immediate imagination-capturing metaphorical impacts, the findings could help scientists understand the population dynamics of wild caterpillars – how they select habitats, and ultimately how populations evolve.

Scientists studying caterpillars in laboratories are also advised to take larval conditioning into account as a confounding factor in their experiments.

Further research, wrote the researchers, "will yield greater insight into the process of complete metamorphosis and move us closer to an integrated understanding of organisms, providing links between complex cognitive behaviors and the molecules and developmental processes that give rise to them."

Indeed. And wouldn't it be poetic if scientists ended up developing treatments for dementia based on the persistence of butterfly memories?

Retention of Memory through Metamorphosis: Can a Moth Remember What It Learned As a Caterpillar?[PLoS ONE]

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Images: Jeffrey Pippen (caterpillar), Illinois State Museum (moth)*

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