JUNE
2007

 

 

 

By
Tom Turpin
 
Professor of
Entomology
Purdue University

 

 

 

 

 

6-28-07

Metamorphosis Means Times Are A-Changin' for Insects

In 1964, Bob Dylan released a new song entitled "The Times They Are A-Changin'" on the album of the same name. The message of the song captured in the title struck a sympathetic chord with many people in the late 1960s.

Things have always changed and continue to do so. The title of the Dylan song, though, has become a popular catch phrase for new things and ideas. For instance, in 1984 Steve Jobs used the phrase when Apple Computer introduced the first Macintosh. In 2001, a worldwide conference held in the Netherlands to address the issue of climate change was entitled--you guessed it--"The Times They Are A-Changin'."

But long before Bob Dylan began singing about changing times, insects were undergoing abrupt and dramatic changes in their lives in a process called "metamorphosis." Indeed, this change in form is one of the reasons that insects are successful organisms. To be sure, there are a few other animals, like frogs, toads and salamanders that also use metamorphosis to their advantage. But when most people think of metamorphosis in the animal world, they think of insects.

The term metamorphosis is defined as a change in form, structure or substance, especially as a result of magic or witchcraft. So the historical use of the term was very appropriate to describe the development process of some insects. In the early days of scientific observation, people did not understand the relationship of some of the immature insects with the adult forms. They even used the term "larva," the Latin word for mask, to describe an immature insect like a caterpillar. The basis for the choice of the word was that they did not know what the immature would become. It's final identify was masked or covered.

Eventually, ancient people discovered that certain larvae, after going into a stage called a "pupa," emerged in a totally different form. Almost like magic the creature had changed into something else. It had metamorphosed!

So what is the advantage of going through this form change? The big advantage is that the immature or baby insect might eat a different type of food or live in a different location than the adult. That means the baby and adult do not compete with each other for food or space. For example, an immature butterfly--a caterpillar--will have chewing mouthparts and might eat the leaves of a plant. The adults have a siphoning tube for a mouth and will feed on nectar.

Some insects, like the dragonflies, live in water as immatures, while the adults live on land. Frogs, toads and salamanders also have immatures that live in the water. The immature frogs and toads are called "tadpoles."

Because of metamorphosis in many insects, today, as in ancient times, it is not easy to tell what an immature insect will turn out to be in the adult stage. Unless of course, you have taken an entomology course on immature insects! But even then, because so many of the immature insects look similar, the identification is a difficult process.

However, many of the immatures of the same type of insect have a similar look. Immatures of flies tend to be tapered, legless, headless creatures that we call "maggots."

Baby butterflies and moths are generally plant-chomping caterpillars. Caterpillars have an obvious head, six real legs and several other leg-like, fleshy appendages called "prolegs" Many beetles in the immature form are C-shaped with an obvious head, and we call such things "grubs." However, many immature forms of bees and wasps look very much like fly maggots but are called grubs. Confused? I guess not much has changed from ancient times. It is probably easier to use the general term larva.

As a larva, the insect is a wingless creature that basically eats and grows. In the adult stage, the insect will often have wings when its main function will be to mate and lay eggs. Metamorphosis in insects means the times are a-changin'--in form and function that is!

 

Writer: Tom Turpin
Editor: Olivia Maddox