Liquid Memories

In 1969, Eric Carle wrote The Very Hungry Caterpillar, a now-classic story of a caterpillar who spends a week foraging for food until it finally morphs into a butterfly. Carle — understandably, given that Caterpillar is a children’s book — skips over what happens when the caterpillar enters its sac, called a chrysalis (which we often, incorrectly, call a cocoon).

The short version: in the chrysalis, the creature turns itself almost entirely into liquid, as seen in the last photo here. Some of the organs are intact in that photo, but over time, as discussed here (one caveat: that link may play audio when you click it), every part of the former caterpillar is converted into a “rich culture medium” — explained here, but basically, liquid — which in turn transforms into a butterfly.

That’s right: the caterpillar melts, liquefying itself on its way to the becoming a butterfly.

Because of this, one may conclude that in a way, the caterpillar and butterfly are two distinct creatures, with one having no knowledge of the other. That would make intuitive sense — a liquified creature simply can’t retain memories created by its former self, nor impart those memories to its future form. But as is often the case, our intuition proves incorrect.

As reported by Science Daily in 2008, researchers at Georgetown University exposed caterpillars to a pungent, specific odor while simultaneously administering a mild shock to the creature. Over time, the caterpillars learned to avoid the odor even in the absence of the shock treatment, in an experiment intentionally reminiscent of Ivan Pavlov’s research with dogs. The caterpillars later metamorphosed into (in this case) moths. The research team then exposed the moths to the same odor.

The moths fled. Somehow, even with their brains turned into goo and reassembled, these creatures managed to retain the memories they created in their previous form.

Bonus fact: One of Pavlov’s dogs (seen here) is stuffed, preserved, and on display in the Pavlov Museum in Russia — replete with a saliva-catcher.

Related reading: We can’t decide: all of Carle’s work is wonderful.