STEWART KNOW-IT-ALL: How do caterpillars change into butterflies?

Maddie Schantz, 3rd grade student at Pine River Elementary School
Maddie Schantz, 3rd grade student at Pine River Elementary School

To answer this question, you must look very carefully inside the caterpillar. Inside its body are some very special cells called imaginal discs. These discs will become the structures of the adult butterfly. The discs are very small in the caterpillar.

When the caterpillar becomes a pupa (or chrysalis), which is the stage right before it becomes an adult butterfly, it dissolves most of its own body in order to feed these imaginal cells. If you opened up the pupa at this point in time, it appears as if it was melted on the inside. However, despite the appearance of tomato soup, the imaginal cells are still there, ready to spring into action. The cells undergo a tremendous amount of growth inside the pupa. Some discs will become the wings (there are four discs for each wing of the butterfly), and others will become the main body parts, including the head, antennae, legs, thorax (middle body segment) and abdomen.

The final step is to emerge from the pupa. The butterfly is surrounded by the pupal covering called the cuticle. The butterfly is trapped inside the pupa, so it either claws its way out, or uses a special chemical to dissolve the cuticle. Since the adult butterfly was squeezed inside the pupa, it has to pump blood into its wings so they can be expanded for the butterfly’s first flight.

Even more amazing is the fact that some moths appear to remember their life as a caterpillar. Scientists from Georgetown University used an electrical shock to train the caterpillars to avoid a certain kind of odor. After changing into an adult moth, they remembered the odor and avoided it just as they learned to do as a caterpillar. So I guess that even butterfly children can learn while growing up!

David Griffith Assistant Professor of Biology at Ferris State University

He teaches has a Ph.D. in Biology from the University of Illinois at Chicago, and a B.S. in Biology from Hillsdale College. He has taught human anatomy and physiology, and general biology at Ferris State University. He has also been published in several scientific publications including the International Journal of Speleology.