Tom Turpin
Professor of
Purdue University


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Flies in the face of fashion

What's Buggin You Now?





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The Two Faces of the Insect World

There are two sides to every coin, and, as an astute reader of this column pointed out, there is more to insects than their pest nature! Truer words were never spoken. However, it is the pest nature of some insect species that gets most of the attention from humans.

Pest insects are like the squeaky wheel that gets the grease. Or the rotten apple that causes the whole bushel to turn bad. In a more modern vein, it is the bad news that gets the headlines. Like it or not, there is truth to these statements.

It is the pest nature of some insect species that is responsible for much of the public's general perception of insects. Entomology is that aspect of biological study that deals with insects. Because of the problems caused by these six-legged creatures, entomology is more prominent than many other areas of specialization in biology.

In the natural systems of the earth, insects are major players. These creatures eat plants, other animals, including insects, and dead stuff. These are what scientists call ecological roles. But when insects eat something that we humans claim as our own, we are unimpressed. We have even created a name for creatures that are doing something we do not like. That name is pest.

Entomologists have historically recognized the two faces of insects. Creatures that on the one hand are indispensable to the natural order of the earth but also create problems for us. That is the reason that one of the most popular textbooks on entomology is titled "Destructive and Useful Insects." This book was first published in 1928 by C. L. Metcalf and W. P. Flint of the University of Illinois. Now in its 5th edition, the book is authored by R. L Metcalf and R. A. Metcalf, son and grandson respectively of C. L. Metcalf. While the authors have changed over the last 75 years, the title remains the same.

A similar title was adopted for an introductory entomology course here at Purdue University. The course title, "Insects: Friend and Foe," reflects that, based on human values, the creatures called insects are sometimes good and sometimes bad. However, from a human perspective, most insects are neither good nor bad because, for the most part, we don't know enough about them to make a judgment. 

Based on personal experience, we generally know about some bad insects. But what are the good things that insects do? Without getting into what scientists call ecological roles, insects are friends in several ways.

One of the most important things that insects do for us is provide products--materials that they make or collect. Silk is such a product. It is produced by the salivary glands of the silkworm caterpillar and is incorporated into the case enclosing the pupae of the silkworm moth. Each cocoon contains a thread about 1000 feet in length. Such strands are wound together to form the threads that will be used for fabrics. Anyone own a silk dress or tie?

Honey is another material that comes to us complements of an insect. Honey results when the "middle insect," a honey bee, takes sips of nectar from the flowers and partially digests it in the honey crop in the trip to the hive. Ultimately, the honey is stored as a food resource for the bees. It is here that humans intercede to harvest the honey. To make the process easier, we keep honey bees in much the same way as we keep other farm animals.

While honey bees don't produce the raw material for honey--that's the job of plants--they do produce wax, which is another product we glean from bees. Wax is produced by hypodermal glands on the abdomen of the bee. It is then used to form the comb that is used to rear larvae and store honey and pollen.

Both honey bees and silkworms are domesticated insects, since humans keep the insects for the purpose of harvesting the products we want. A few other insects also give use products, even though we don't keep the insects. For example, shellac comes from scale insects called lac insects. The lac functions to protect the insect from the weather. Historically, we have used the material as a wood finish. Some gall insects provide dyes for ink, and the cochineal insects give us dyes to color fabric.

Do you like honey on your breakfast toast? Do you use bee's wax in a beauty treatment? Do you wear silk? If you answered "yes" to any of these questions, I'll mark you down as one who appreciates the usefulness of insects!



Writer: Tom Turpin
Editor: Olivia Maddox