Does the Butterfly Remember?

The story

You know the story. A caterpillar munches leaves, grows fat and happy, then goes still and sheds its skin one last time, and what remains is a new form called a pupa. A butterfly pupa is called a chrysalis, and many moth caterpillars first spin a silk cocoon around themselves for shelter. Later, a winged creature climbs out and flies away. It sounds like a simple costume change. It is one of the strangest transformations in nature.

Because inside that quiet case, the caterpillar does not simply sprout wings. Much of its body is taken apart. Many caterpillar parts break down into a rich, nourishing mush, while special groups of builder cells, some of them present from the caterpillar's earliest days, use those recycled materials to grow new things. New wings. New legs. New eyes. Other parts, including pieces of its nervous system, are not thrown away at all, but carefully remade for the new life in the air.

Which leads to a riddle. If so much of the body is taken apart and rebuilt, what happens to everything the caterpillar knew? Does the butterfly remember?

Scientists in America put the question to a careful test, working with hawkmoths, night-flying cousins of butterflies with the same great transformation. First, they gave caterpillars one particular smell, paired each time with a small electric shock. After several rounds, the trained caterpillars would crawl away from that smell. The lesson was learned. That smell means bad news. Then the caterpillars pupated, went through the great rebuilding, and came out as moths.

And when the scientists offered the grown moths that same smell, the moths avoided it. The lesson had survived. Learned as a crawling leaf-muncher, remembered as a flying moth, straight through the great rebuilding. Not every memory makes it, and timing matters. Scientists suspect some threads of the nervous system survive the rebuilding and carry it, though exactly how is not yet known.

And the story does not end in the laboratory. In Japan, an eight-year-old boy named Jo, who raised swallowtail butterflies at home, wondered whether they remembered their caterpillar days. He wrote to Doctor Martha Weiss, the scientist behind the moth experiment, then adapted the experiment himself to run at home, using a muscle-therapy machine for the tiny shocks. Jo trained his caterpillars, waited through the great rebuilding, and offered the butterflies a little maze with the training smell down one arm. Most of them steered away from it. He shared those results with scientists that same year, and two years later, at ten years old, he presented his work to a grand gathering of insect scientists.

So a creature can be rebuilt into a different shape, for a different life, in a different world, the air instead of the leaf, and still carry something of who it was before.

So the next time a butterfly or a moth drifts past you in the warm air, give it a moment of respect. That little flyer once wore a completely different body, and somewhere inside it there may still flicker a faint, faithful whisper of its caterpillar days.