Butterflies melt into goo then rebuild

A caterpillar does not grow wings inside its cocoon; it dissolves into a biological soup first. Enzymes released during metamorphosis digest almost every tissue in its body until it is a bag of nutrient-rich protein liquid.

Only a few specific clusters of cells, called imaginal discs, survive this total meltdown. These discs are essentially blueprints for the future butterfly, containing the instructions for legs, eyes, and wings.

As the caterpillar's old body turns to mush, these discs use the liquid protein soup as fuel to rapidly build the butterfly's new anatomy. It is one of the most radical structural changes possible in the animal kingdom.

Even more unsettling is that the soup remembers. Experiments show that if you train a caterpillar to avoid a specific smell, the butterfly that emerges from the liquid goo weeks later will still fear that same smell.

This suggests that while the brain undergoes massive reorganization and remodeling, key parts of the nervous system stay intact to preserve the butterfly's memories through the chemical chaos.