All bugs are insects, but not all insects are bugs

I have always called insects bugs.  I know I’m using the wrong word most of the time since the word bug refers to a specific group of insects.  If I’m not talking about that one group, using the word bug instead of insect is technically incorrect.  If you’re around many entomologists , using the word bug to describe an insect that is not actually a bug is like scraping your fingernails down a chalkboard – highly annoying.  I don’t know. I’ve always found this attitude somewhat pretentious and counterproductive.  As an entomologist myself, I like to promote insect awareness and get people interested in what I do.   It’s hard to get people interested in what you do when they feel belittled because you corrected them for using a word they didn’t even know was wrong.  I use the word bug for all insects, even though I know I am wrong to use it most of the time (and yes, I have been corrected by other entomologists myself!), for several reasons:

1) It’s easier to say bug than insect.

2) I find people relate better to stories about bugs than stories about insects, especially when they know I’m an entomologist or if they are kids.

3) I happen to work with insects that are, in fact, bugs.  When you constantly use the word bug to describe your work, even in scientific papers, you get in the habit of using the word bug all the time.

Really, though, how many people who aren’t entomologists know the difference between an insect that is a bug and an insect that is not?  It’s a subtle distinction and most people don’t have any reason to learn the difference.  For those of you who don’t know what makes a bug a bug, allow me to enlighten you!

The insects are divided into about 25 smaller groups called orders.  All insects belonging to an order share certain traits, which is why they are grouped together in the first place.  A bug is an insect that belongs to the order Hemiptera.  Members of the order Hemiptera are also called true bugs, hence the word bug.  If you’re being technical, only insects that are true bugs should be called bugs and everything else should just be called an insect.  But how do you tell a true bug apart from other insects?  All true bugs share two main traits: hemielytra and piercing-sucking mouthparts.

The word hemielytra refers to the specialized top pair of wings (forewings) of the true bugs.  Most insects have 4 wings and true bugs are no exception.  Some insects, like beetles, have hardened forewings that protect the more fragile hindwings underneath.  These are called elytra.  Take a look at this palo verde beetle’s elytra:

palo verde beetle

A beetle. The arrow points to this beetle's elytra.

The true bugs have hemielytra, not elytra.  The forewings of bugs are only hard for part of their length instead of the entire length.  The upper part is thick and leathery and the lower part is membranous, about the same texture as the hind wings underneath.  Look at the forewings of this giant water bug and look for the differences in these wings compared to those of the beetle pictured above:

Lethocerus

Giant water bug. The arrow points to the hemielytra.

See the dark section of the wing toward the back end of the bug (to the right of the tip of the arrow)?  That’s the membranous part.  The rest of the wing is the thickened, leathery part and a completely different texture.  True bugs often have a sort of V-shape to their wings.  See the V just to the left of the tip of the arrow?  For the most part, if you see this V-shape in the wings of an insect, you’re looking at a true bug.  (Note: I’ll talk about that big, long piece sticking off the back of the giant water bug in a future post.)

The other trait that all true bugs have is piercing-sucking mouthparts.  Different insects have different types of mouthparts, but most people are familiar with insect chewing mouthparts.  This is what caterpillars, beetles, and grasshoppers have.  They use these mouthparts to grind their food up before swallowing it as the first step in digestion.  Look at the chewing mouthparts of the palo verde beetle:

palo verde beetle head

Palo verde beetle head. The arrow points to the chewing mouthparts.

Palo verde beetles have really big mouthparts that are easy to see.  These things can actually bite quite hard, even drawing blood if they get you in the right place!

In contrast, true bugs have piercing-sucking mouthparts.  Instead of putting food into their mouths and grinding it up the way beetles do (and humans too!), they inject digestive chemicals into whatever they want to eat using their mouthparts (hence the piercing part of “piercing-sucking mouthparts”).  These chemicals break the food down into a soupy mess which the bugs then suck into their mouths through their mouthparts (that’s the sucking part of “piercing-sucking mouthparts”).  It’s a lot like eating your food with a straw!  Check out the mouthparts on the giant water bug:

true bug bealk

Giant water bug mouthparts. The arrow points to the piercing-sucking mouthparts.

The piercing-sucking mouthparts of true bugs are often called beaks because they are long and pointy like a bird’s beak.  Can you see the similarity?  Unlike birds, bugs can fold their beaks down under their heads, which is how the beak of the giant water bug above is positioned.

An interesting aside: Bugs can have a really nasty bite.  That little straw-like mouthpart might not look that impressive, but remember how bugs eat: they inject digestive chemicals into their food.  If you handle one improperly or startle one, those same digestive chemicals can end up in your fingers!  They can’t do any lasting damage, but it can hurt a lot as it digests some of your muscle.  It’s usually a good idea to handle true bugs with care.

So now you know!  A bug is an insect that has hemielytra and piercing-sucking mouthparts.  The next time you want to get technical and use the word bug for an actual bug, think about whether the insect in question has that V-shape to its wings and a long beak folded down under its head.  If so, it’s a bug and you can use the word bug without fear or hesitation!  If not, you can still call it a bug.  The choice is yours after all.  Just expect any entomologists nearby who happen to overhear you to correct you.

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