What makes an insect an insect?

As an entomologist, the first thing I think when I see an insect is ‘What is it?!’ But that is often a harder question than it seems, and it has many answers. First things first, is it an insect? Identifying organisms is hard! They whole field of taxonomy is dedicated to figuring out how to classify, group, living organisms. The system we use is called the Linnaean classification system. In this system organisms are grouped into Kingdoms, Phylum, Class, Order, Family, Genus, and then Species. Insects are all in the Phylum arthropoda.

But how can you tell an insect is an insect? Well, luckily, there are a couple simple rules for this. The first one is that insects have six legs, three on each side.

Insects have six legs

The next useful clue is that insects have three body segments: head, thorax, and abdomen, in that order. The legs come out of the thorax.

Insects have three body segments

Insects have three body segments

Insects also almost all have antennae of varying lengths.

Insects have antennae

Insects have antennae

This is my favorite part when I’m teaching kids because I ask them these two questions. 1) How many legs to spiders have? And 2) are spiders insects? The surprise on their faces when they answer ‘no’ is priceless. Pill bugs, also not insects (way too many legs!). I’m certainly not saying that I don’t like other small organisms, just that in order to figure out what you are looking at determining if it’s an insect is a good first step

Once you know it’s an insect, then you can get down to the real business of what type of insect you have! The next step is to identify what order the insect belongs to. There are many insect orders and some don’t have great defining characteristics. However, some of the most common do. Here’s a couple to get you started.

Order Hymenoptera: Bees, wasps, parasitoids, ants

Insect in the order Hymenoptera have 2 pairs of wings (4 wings total), except worker ants which have no wings. They have a thin waist connecting their thorax and the lower abdomen. Females have prominent ovipositor, mostly this is used for laying eggs but is modified in some groups to be a stinger. Their antennae are usually longer than their head and have greater than 10 segments.

Spider wasp

Spider wasp

Honey bee

Honey bee

Order Coleoptera: All beetles including lady beetles, leaf beetles, soldier beetles

All insects in the order Coleoptera have hard outer wings.


Order Lepidoptera: Butterflies and moths

They have 4 wings, covered with scales. Their mouthparts are shaped like a long straw and called a proboscis; it is kept curled up.

Larvae are commonly known as caterpillars.

lepidoptera lepidoptera2 Caterpillar

Order Hemiptera: Aphids, assassin bugs, leaf hoppers

There are many, varied insects in the order Hempitera. They have one very useful defining characteristic: their mouthparts are shaped like a straw. It is often kept tucked underneath their face.


There are many more of course. But that’s a start for now!


About keviclaire

I recently graduated from the Department of Environmental Science, Policy and Management at UC Berkeley. My research interests are focused on biological control and how to increase it's use in agriculture and home gardens. I am also an avid gardener and insect photographer. I'm using this blog as a place to share those interests!

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