I saw a caterpillar and a butterfly in the neighbor's yard. So my question is, what exactly happens inside the little sack they're in while they transform into a butterfly and HOW exactly do they do it?  -Eston

Dear Eston,

Springtime sets the stage for one of the greatest transformations in the natural world.

“It’s the construction of a butterfly or moth from caterpillar soup,” said my friend David James, an entomologist at Washington State University. James studies the science behind metamorphosis, or how a creature transforms.

Before becoming butterflies, caterpillars enter the pupa stage, where they build that little sack, or chrysalis. The chrysalis protects the caterpillar as it begins to turn itself into a liquid, soupy substance.

Caterpillars are born with everything they need to become butterflies. Some of these parts develop over time and are visible, like wing buds. The others can’t be seen. But the information for these parts is stored in the caterpillar’s cells, waiting to be unlocked. The caterpillar is also born with the ability to make a substance called an enzyme. The enzyme is a key to unlocking the butterfly from the chrysalis.

During the first couple days of living in the chrysalis, the caterpillar’s enzymes will eat the caterpillar itself. Bit-by-bit, they unlock the information from the caterpillar’s cells. The new butterfly’s organs, wings, antennae, and legs form inside the chrysalis.

With new technology, scientists can peer into the chrysalis. They can see that the pupa is breathing through small tubes and actually watch the different parts start to grow.

It all happens very quickly, sometimes in just a week, James said. A few days before the butterfly emerges from the chrysalis, its parts finish forming. Then, the chrysalis turns a very a dark color. About 24 hours before the butterfly comes out of the chrysalis, colors and patterns start to develop on the wing cases that cover the forming wings.

“The butterfly begins pushing with its feet against the shell covering its legs, antennae and proboscis,” James said. The proboscis is the long coiled mouth-trunk it will use to drink nectar.

Butterflies come out very soft, so their wings are pretty droopy. Blood goes out their body and starts circulating up throug
h their wing veins. This helps their wings stand up.

“After another hour or so the wings are dry and the butterfly or moth can take its maiden flight,” James said.

While scientists are discovering more about what goes on inside the chrysalis and how it happens, they are still eager to discover exactly why it happens at all.

James suspects it has to do with how they evolved. Caterpillars and butterflies eat different parts of plants. Caterpillars like leaves and butterflies like to drink nectar. Since they don’t have to compete for the same food, it makes it easier to survive. Metamorphosis also helps the insect make new colonies and reproduce, James adds.

While it’s possible to do this when inching around, species can go faster and further when they spread their wings and fly.

Sincerely,

Dr. Universe