What's the Difference Between Bugs and Insects?

tl;dr

All bugs are insects, but not all insects are bugs. In everyday language, “bug” can refer to any small creature that crawls or flies. But scientifically, “true bugs” are a specific group of insects in the order Hemiptera , which includes things like stink bugs, aphids, and cicadas. What makes them special? Their straw-like mouthparts and leathery wings.

Most people use the word “bug” to mean just about any little creepy-crawly. Beetle on the sidewalk? Bug. Mosquito in your ear? Bug. Spider in the shower? Definitely a bug.

But ask an entomologist, and you'll get a very different answer.

So what is a bug, really?

Scientifically speaking, the term “bug” refers only to a specific order of insects known as Hemiptera . These are the “true bugs” - a group with some very particular features that set them apart.

That means while all bugs are technically insects, the reverse isn't true. Butterflies, ants, beetles, and flies are all insects, but they aren't bugs.

So where's the line drawn?

What Makes an Insect an Insect?

Let's start broader. Insects belong to the class Insecta , and they all share some defining traits:

• Three-part body: head, thorax, and abdomen
• Six legs attached to the thorax
• One pair of antennae
• An exoskeleton made of chitin
• Most adults have wings
• All undergo some form of metamorphosis

This group includes more than a million described species —more than half of all known animal species on Earth¹ .

What Sets True Bugs Apart?

Now, zoom in to the order Hemiptera , which includes around 80,000 species of true bugs²³ . They stand out in a few key ways:

1. Mouthparts Like Needles

True bugs have piercing-sucking mouthparts called stylets ⁴⁵⁶ . These act like tiny drinking straws or syringes. They use them to feed on plant sap—or in some cases, blood.

This proboscis doesn't roll up like a butterfly's—it's stiff and permanently extended, like a needle⁴⁶⁷ .

2. Unique Wings

Their front wings are part leathery and part see-through, a combination called hemelytra —“half-winged” in Greek⁸⁹ . When folded, they lay flat across the back in an overlapping X shape.

3. Life Cycle: No Pupa

True bugs go through incomplete metamorphosis : egg → nymph → adult⁴⁶³ . Nymphs look like miniature adults without wings.

That's different from insects like butterflies or beetles, which go through a full transformation including a larval and pupal stage.

Examples of True Bugs

Here's a short list of critters that qualify as true bugs:

• Stink bugs
• Aphids
• Cicadas
• Bed bugs
• Assassin bugs
• Leafhoppers
• Water striders

Common Insects That Are Not True Bugs

Despite the name, these are not scientifically considered bugs:

• Ladybugs (actually beetles)
• Bees and wasps
• Butterflies and moths
• Flies and mosquitoes
• Ants and termites
• Cockroaches

Still insects, but not Hemiptera.

Wait, So Why Do We Call Everything a Bug?

Blame history.

In 13th-century English, “bugge” referred to something frightening—like a scarecrow or hobgoblin¹⁰ . That association with fear eventually stuck to nighttime nuisances like bed bugs.

By the 1600s, “bug” was being used for insects. When Linnaeus formalized taxonomy in the 18th century, he grouped certain insects together as Hemiptera , cementing the concept of “true bugs”¹⁰ .

So yes, “bug” became both a casual nickname and a technical term—but for different things.

Final Thoughts

Every time you swat a mosquito or admire a butterfly, you're looking at an insect. But unless it's got piercing-sucking mouthparts and half-leathery wings, it's probably not a true bug.

And while the everyday use of “bug” is perfectly fine in casual conversation, understanding the scientific meaning adds a fun (and surprisingly complex) layer to the way we think about the miniature creatures around us.