Butterflies and moths have very unusual life cycles

"How do caterpillars make cocoons?" asked a preschooler at the Libertyville Recreation Department Kinder Korner Preschool program.

Moths and butterflies are similar in many ways, but their path to adulthood sets them apart.

They miraculously lift their tiny bodies using wings bedecked in hues and patterns that span the imagination. Both are holometabolous, meaning they mature through a process called metamorphosis.

The journey takes the insect from its beginnings as a tiny egg, then it changes into a larva - that's the caterpillar - next pupa, and finally it emerges as an imago, another word for an adult.

When a butterfly experiences the pre-adult pupal stage, also called a chrysalis, it lives as a non-hibernating insect and prepares for its final adult stage. For many moth species, the pupa uses silk to spin a protective cocoon, and inside that cocoon the pupa transforms into an adult moth.

"If you look carefully at the chrysalis," said Doug Taron, Ph.D., chief curator at Chicago's Peggy Notebaert Nature Museum, "you can see the emerging adult structure fused to the outer structure - the legs and the antenna."

Taron cautions that people often confuse the chrysalis with a case or cocoon, but they are not the same.

The moth caterpillar's main job is to eat, and then it weaves a cocoon when hormones push it to the final stage of adulthood.

"A cocoon is a structure the caterpillar builds for itself using silk, a protein," Taron said. "It uses special glands called spinnerets to make silk, which is created out of food it metabolizes."

Spinnerets are found on either side of a caterpillar's mouth. For some silk moths, the silk produced is so strong and eye-catching that farmers harvest the cocoons so it can be sold to make silk fabric.

The main job for the imago is to mate and lay eggs, so most adults no longer have mouths.

While the cocoon is a protective cover, it is not entirely sealed. With great care, the pupa can be removed and returned.

"The museum's Judy Istock Butterfly Haven often has huge Atlas moths with one-foot wingspans. The cocoon has a little opening at one end where they can force their way out," Taron said.

From time to time, exhibit caretakers gently remove the pupa so museum guests can observe the almost adult pupa.

Once the imago has emerged, there's no need for the cocoon, and it rots, Taron said.

"I suspect most are degraded by microbes."

Illinois is home to nearly 2,000 moth species according to the Illinois DNR website. A good guide for identifying moths and butterflies, Taron suggests, is "Caterpillars in the Field and Garden: A Field Guide to the Butterfly Caterpillars of North America" by Thomas J. Allen.

Ever wonder what insects and other backyard creatures do when the sun sinks into the horizon?

The Peggy Notebaert Nature Museum's new exhibit, "Backyard Adventures," offers visitors a bee's-eye-view into the nighttime adventures of millipedes, bees beetles, praying mantises, large milkweed bugs, birds and mammals.

Even plants have a night life that visitors can explore.

For more information, see the museum website at www.naturemuseum.org.

Check it out

Cook Memorial Library in Libertyville suggests these titles on butterflies and moths:

• "Butterflies," by Marfé Ferguson Delano

• "Caterpillar to Butterfly," by Lisa Herrington

• "Caterpillars and Butterflies," by Trudi Strain Trueit

• "Arabella Miller's Tiny Caterpillar," by Clare Jarrett

• "The Case of the Missing Caterpillar: A First Look at the Life Cycle of a Butterfly," by Sam Godwin