FEBRUARY
1997

 

 

 

By
Tom Turpin
 
Professor of
Entomology
Purdue University

 

 

 

 

 

02-25-97

Insects Are Schizophrenic

Psychologists would no doubt classify many insects as schizophrenic. After all, during their lives, several species of insects clearly possess a split personality. But unlike human schizophrenics, these insects not only have a change in personality, they also look different! That is because of a biological process known as metamorphosis. Through metamorphosis, the insects change between forms that are distinctly different in the way they look, in the types of food they eat, and in the way they behave.

The forms are so completely different that we have different names for each. Maggots, caterpillars and grubs are terms used for immatures of some insects. The corresponding adults are called flies, butterflies and beetles.

For insects, changing personalities is not a quick change, it is a major undertaking. To do so the insect employs a variation of the old superman trick of running into a telephone booth. The change of the immature to the adult occurs in a stage during which it's known as the pupa.

In the pupal stage, the insect undergoes a remarkable remaking that surpasses the best work of the most skilled plastic surgeons. But the insect starts at the ground floor. It doesn't simply readjust what is already there, it starts over. Old tissues from the immature are broken down and reassembled into the new adult.

In general, the pupal stage of insects is immobile. A pupa can wiggle around a little, but it is incapable of moving from place to place. Thus the insect pupa cannot run away from predators or move to get out of the sun or rain. So the immature insect has to seek a place for pupation. A caterpillar may crawl several meters looking for just the right spot to pupate. When it finds a suitable location, it will form a cell in the soil, fold leaves around itself or spin a cocoon.

Some of the most conspicuous pupae belong to the butterflies and moths. Generally, moths cover their pupae with cocoons, although some do not. Cocoons are spun of silk, and it is from the cocoon of the silkworm that we produce the silken thread that is used to make silk cloth. The pupae of butterflies are known as naked pupae since they do not spin cocoons. As a rule, these naked pupae are attached to twigs or leaves.

Pupae of butterflies and moths are known by the name chrysalis, which is based on the Greek root "chrys," meaning "gold." We find the same root in "chrysanthemum," which literally means "gold flower." The basis for the name was that some butterfly chrysalids, such as that of the monarch, have prominent gold flecks. What a story! An ugly plant-devouring, crawling worm disappears behind a gold-flecked cape and emerges as a beautiful, winged butterfly.

 

Writer: Tom Turpin
Editor: Andrea McCann