The word bug is often used as a generic term to refer to any type of small crawling critter, and it is not only kids and unknowing adults who use the term this way. Many scientific experts, even trained entomologists, will use the term "bug" to refer to a wide range of small creatures, especially when they are speaking conversationally to the general public.
The Technical Definition of a Bug
Technically, or taxonomically, a bug is a creature that belongs to the insect order Hemiptera, known commonly as the true bugs. Aphids, cicadas, assassin bugs, ants, and a variety of other insects can claim rightful membership in the order Hemiptera.
True bugs are defined by the types of mouthparts they possess, which are modified for piercing and sucking. Many members of this order feed on plant fluids, and so their mouths have the structures necessary to penetrate plant tissues. Some Hemipterans, such as aphids, can badly damage or kill plants by feeding in this way.
The wings on Hemipterans, the true bugs, fold over one another when at rest; some members lack hind wings altogether. Finally, true bugs always have compound eyes.
All Bugs Are Insects, but Not All Insects Are Bugs
By the official definition, a large group of insects aren't considered bugs, although in common usage they are often lumped together under the same label. Beetles, for example, are not true bugs. Beetles are structurally different from the true bugs of the Hemiptera order, in that their mouthparts are designed for chewing, not piercing. And beetles, which belong to the Coleoptera order, have sheath wings that form hard, shell-like protection for the insect, not the membrane-like wings of the true bugs.
Other common insects that do not qualify as bugs include moths, butterflies, and bees. Again, this has to do with structural differences in the body parts of these insects.
Finally, there are a number of small crawling creatures that are not insects at all, and so cannot be official bugs. MIllipedes, earthworms, and spiders, for example, do not possess the six legs and body segment structures found in insects, and are instead members of different animal orders-spiders are arachnids, while millipedes are myriapods. They may be creepy, crawly critters, but they are not bugs.
Calling all insects and all small crawling creatures "bugs" is a colloquial use of the term, and when scientists and otherwise knowledgeable people use the word in such a way, they are usually doing it to be down-to-earth and folksy. Many highly respected sources use the word "bug" when they are writing or teaching certain audiences:
- Gilbert Waldbauer is a respected entomologist from the University of Illinois. He authored an excellent volume called "The Handy Bug Answer Book" which covers everything from scorpions to silverfish.
- The University of Kentucky's entomology department hosts a website called the Kentucky Bug Connection. They include information on keeping pet bugs, including tarantulas, mantids, and cockroaches, none of which are actually bugs.
- The University of Florida's entomology department has sponsored a "Best of the Bugs" award honoring for outstanding insect-related websites. Among their honorees are sites on ants, beetles, flies, and butterflies-no actual true bugs.
- Iowa State's entomology department hosts one of the best arthropod sites around-Bugguide. The site is a database of information and photographs collected by amateur naturalists, covering virtually every North American arthropod. Only a small portion of the species listed belong to the order Hemiptera.
A bug is an insect, but not all insects are bugs; some non-insects that are called bugs are neither bugs nor are they insects. Is everything clear now?