JULY
2010

 

By
Tom Turpin
 
Professor of
Entomology
Purdue University

 

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Check out these books by Tom Turpin:

Flies in the face of fashion

What's Buggin You Now?

 

 

 

07-08-10

Download the audio of On Six Legs: MP3, WMV.

Caterpillar Encounters Can Be Learning Experiences


Swallotail caterpillar
Swallowtail caterpillar on a parsley plant. Photo by Suzanne Upton

In the good old summertime human and caterpillar encounters are a common event. That is especially true if you are a gardener, a farmer or a kid. Regardless of age, occupation or avocation you generally end up learning something when you come face to face with a caterpillar.

For gardeners or farmers the presence of caterpillars might indicate a pest problem. Then it is decision time! People who grow plants often have to decide if control is necessary to eliminate caterpillars that are making a meal out of foliage.

Technically caterpillars are larvae of insects in the order Lepidoptera. Many people refer to caterpillars as worms. Regardless of the name, a caterpillar, after feeding, forms a pupa and then emerges as an adult insect.

Some pest caterpillars turn into butterflies. Caterpillars of the white-colored cabbage butterfly are green worms that feed on cole crops, such as cabbage, broccoli and cauliflower. As a caterpillar, the painted lady butterfly sometimes feeds on soybean plants.

Other pest caterpillars become moths in the adult stage. These include corn earworms, European corn borers and armyworms. The tomato hornworm caterpillar also becomes a moth and is known by various names, including hawk moth, hummingbird moth or Sphinx moth.

For kids, the discovery of a caterpillar feeding on a plant or just crawling along the ground is an exciting event and reason enough to ask questions. The first question is usually, "What is it?" That is not an easy question to answer. There are thousands of types of caterpillars and many look similar. In fact many caterpillars are so much alike that the only way to tell them apart is by using a diagnostic key with the aid of a high-power microscope to get a close up look at the critter.

For most people, comparing the caterpillar to pictures in a book such as the Golden Guide for butterflies and moths or looking up photos on Google is a good place to start. Either way, it helps to have some idea about the type of caterpillar in question. In general, moth caterpillars are hairy and butterfly caterpillars smooth-bodied. There are exceptions to this rule. Some moth caterpillars are smooth-bodied: the familiar tomato hornworm caterpillar, for example.

Other things to note when trying to identify a caterpillar are size and color patterns. Also, unusual protrusions on the body might allow you to put a name on the caterpillar. Such things as the horn on the tail end of the hornworm or the fleshy antennae-like protrusions behind the head of the monarch caterpillar can be useful for identification purposes.

Another common question about caterpillars is, "What do they eat?" This is a common question from people who find caterpillars on the ground and want to feed them. Caterpillars are sometimes finicky eaters and will only feed on one species of plant or on the type of plant where they began feeding. One thing to remember about caterpillars is that at some point they stop feeding and look for a place to become a pupa. They don't need food after this!

One notable caterpillar encounter in popular literature is described in Chapter 5 of "Alice in Wonderland." Alice encounters a blue caterpillar sitting on a mushroom smoking a hookah. The caterpillar questions Alice about who she is and finds out that she is not really herself and is having an identity crisis. She is distressed that she is only 3 inches tall, a height the caterpillar finds to be quite satisfactory. The caterpillar then asks the question that humans often ask about caterpillars: "Who are you?"

The "Who are you?" question is sometimes asked by home gardeners when they encounter a caterpillar on their parsley, dill or fennel. The striking black- and green-striped caterpillar with yellow dots becomes the black swallowtail butterfly. When disturbed, the caterpillar has an interesting habit of protruding a forked scent gland called an osmeterium from behind its head. Then it releases a disagreeable odor, which conveys the message, "I don't care who you are; just leave me alone!"

Only in books such as "Alice in Wonderland" can caterpillars talk. However, in nature, caterpillars can sometimes send a powerful message just by the way they look or act. And that means a caterpillar encounter can be a learning experience for a human.

 

 

Writer: Tom Turpin
Editor: Olivia Maddox