What is a true bug?

Most people refer to all insects as bugs. During our rambles we often see insects that I refer to as "true" bugs and today Hugh asked me what a true bug was. Here's my attempt to clarify.

Insects are divided into groups called "Orders." Each Order contains a different type of insect. For example, beetles comprise one Order, the Coleoptera (pronounced co-lee-AWP-tare-uh). Butterflies and Moths make up another Order, the Lepidoptera (pronounced: lep-eh-DAWP-tare-uh). In all there are around 25-30 different orders, some composed of insects most people have never heard of. The characteristics often used to separate the different orders are the nature of the wings and the mouthparts. For example, the butterflies and moths have two pairs of wings that are covered with powdery scales and have sucking mouthparts that are coiled up like a watch spring beneath their head.

The features that distinguish true bugs from other kinds of insects are 1) piercing, sucking mouthparts, 2) two-part forewings and 3) a triangular "scutellum" between the bases of the forewings. Now let me explain what these three characteristics mean.

Piercing, sucking mouthparts are also found in insects like cicadas, aphids and leafhoppers, among others, so it is not unique to the true bugs. 

But the structure of the front wings is unique. They are leathery at the base and membranous at

the end. In the sketch of a stink bug to the left I've labeled the two parts of the right forewing; "a" is the leathery base and "b" is the membranous part. Notice how the membranous parts of the left and right forewing overlap when the bug is at rest. (True bugs have a pair of hingwings, too. They are folded up and concealed beneath the forewings when the bug is at rest.)

The third feature, the scutellum, is a triangular part of the exoskeleton that is located between the bases of the front wings. It is labelled "c" in the sketch. Only the beetles have a scutellum and it is very small compared to that of the true bugs.

In older systems of classification the true bugs belonged to the Order Hemiptera (pronounced he-MIP-tare-uh) and cicadas, aphids and other, related kinds were assigned to the Order Homoptera (pronounced ho-MOP-tare-uh).  These names refer to the structure of the forewings. Hemiptera means "half wing" and refers to the difference between the base and apex of the wing. Homoptera means "whole wing" and refers to the fact that cicadas have completely membranous forewings. This classification you will find in most books published before 2000.

 In the 1990s the classification was revised and the Order Hemiptera expanded to include the old Order Homoptera. So the true bugs could not be called Hemiptera anymore, because the meaning of the label had been expanded to include other types of insects. The true bugs were assigned to the Suborder Heteroptera (pronounced het-er-OP-tare-uh) and the other, non-true bug Hemipterans were assigned to their own Suborders.

So what do I say when someone asks me what kind of bug this is? If I say it is an hemipteran they are unlikely to know what I'm talking about. Similarly for a heteropteran. If I say it is a bug, that is not specific enough because in most peoples mind "bug" means insect or creepy-crawly thing. So I'm reduced to saying it's a true bug, unless I know what kind of true bug it is. Then I can say "stink bug" or "leaf-footed bug" or whatever kind of true bug it might be.