FEBRUARY
1998

 

 

 

By
Tom Turpin
 
Professor of
Entomology
Purdue University

 

 

 

 

 

02-12-98

A Creepy Crawly By Any Other Name...

Entomology is defined as a branch of zoology that deals with insects. The word is based on Greek, using the combining form "entomo." The combining form is from the Greek word entomon, which itself is a combination of words that means "cut in two." The word insect is based on the Latin word insectum, from insecare, which means "to cut in." So in both the ancient Greek and Latin languages, the creatures known as insects got their name because of their divided appearance.

But insects aren't the only animals on the earth that appear to have divided bodies. Such things as spiders, millipedes, centipedes, lobsters, ticks and mites all are divided into obvious sections. The ancient Greeks probably lumped many of these "divided" creatures into their term entomon. We tend to do the same thing today. Many people think of spiders, ticks and mites as insects.

Technically, all of these divided creatures are arthropods but not all are insects. So people who call spiders insects might have been correct in ancient Greece, but not today. How can the various arthropods be distinguished from each other?

Insects have three distinct body sections, head, thorax and abdomen. The head is where, as with many other land animals, the mouth and eyes are located. The insect head also has one pair of segmented antennae. The insect thorax contains three pairs of legs and might have wings. So if it has six legs and flies, you can be sure scientifically it is an insect.

Spiders and mites, compared to insects, appear to have lost their heads. They have two body sections and no antennae. And they have eight, not six, legs. So a creature without a head, walking on eight legs is a tick or a spider and is correctly classified as an arachnid. Scorpions and mites are also arachnids.

Another major group of arthropods are the crustacea. Generally crustaceans live in water and include such familiar creatures as lobsters, shrimp and crayfish. The name crustacean comes from the hard shell that covers their bodies. Compared to insects, though, there are two major differences. First, crustacea have more than two antennae. Look closely the next time you are eating shrimp or lobster! Also they have more than six legs. Check out the shrimp cocktail! One common crustacean is not found in water. It is the creature known as the pillbug, sowbug or roly poly. Even though it is called a bug, it is not an insect.

While scientists are careful to distinguish between groups of arthropods, many people are still like the ancient Greeks and lump the arthropods together under a general heading, that of creepy crawly!

 

Writer: Tom Turpin
Editor: Andrea McCann