OCTOBER
1989

 

 

 

By
Tom Turpin
 
Professor of
Entomology
Purdue University

 

 

 

 

 

10-13-89

Presto Chango!

Long before Dr. Jekyll transformed into Mr. Hyde, some insects had already mastered the ability to change their personalities.

These insects use a unique biological process called metamorphosis to change from one life form to another. By this process, a “Mr. Hyde,” or a larva that can damage plans by its feeding can become a Dr. Jekyll, or usually harmless and sometimes beautiful adult insect.

Frank Kafka addressed the concept of metamorphosis in his work of fiction by the same name. A popular movie of more recent times, “Cocoon,” also drew parts of its theme from the process of metamorphosis. Even Yuppies have noted the parallel between a quiet time in their own hurried lives and the apparent quiet of an insect undergoing pupation. In Yuppie lingo, a lazy day of lounging at home is known as “cocooning.”

Changes in the insect during metamorphosis are miraculous. The tissues and organs or the larva are broken down and reassembled. The result is to produce a winged, adult insect, completely different from the wingless eating machine of its youth.

The insect stage that harbors these changes is the pupa, from the Latin word for doll. Apparently, ancient people saw in that insect form a likeness to the inanimate toy for a child. The same Latin root is used to form the word “puppet.”

Insects protect their pupae in a variety of ways. Some, like the common housefly, are thrifty, using their last larval skin to form a protective cover for the pupae. Other insects, like that pest of lawns—the white grub—industriously form a nice chamber in the soil at pupation time. Still others follow the Boy Scouts' lead and make a tent-like structure by tying the edges of leaves together.

Some insects spare no expense or trouble to make their cocoons. Probably the most famous of this group is the silkworm, which spins a cocoon of silk for pupation. Centuries ago, it was discovered that the silken thread used by silkworm larvae to construct pupation chambers could be unwound and used for human purposes. Since that time, uncounted silkworms have sun up cocoons with the biological intent of becoming an adult. However, humans have interceded to claim the silk for their own uses.

And then there are those insects that choose the no-frills method. Most butterflies—unlike their close relatives the moths—have pupae that are naked. As larvae, these streakers among the insect pupae normally attach their tail end to a leaf or twig before pupating. Then while the butterfly pupae, called a chrysalis, hangs upside down, Mother Nature gives the creature a makeover.

Of course this is absolutely necessary. How else would an ugly caterpillar turn into a beautiful butterfly?

 

Writer: Tom Turpin
Editor: Carol McGrew