Insects can be divided into approximately 30 ‘orders’, or groups of more closely related species. These groups can look wildly different from one another depending on the adaptation of the species within them. Dragonflies, beetles and butterflies look very different and have all adapted to different habitats and ‘ecological niches’, but species across these roughly 30 orders still share some common characteristics.

The important thing to remember is that while these common features will look different across different groups of insects, the underlying structures and functions are the same.

Above is a typical body plan for an insect, showing the main parts that most insects share.

Head, Abdomen and Thorax
Insects have three distinct sections to their body: the head, the thorax, and the abdomen. The head is where we find their eyes, antennae, mouth parts. The thorax usually carries three pairs of legs as well as one or two pairs of wings in some species. Finally, the abdomen houses most of the internal organs of the insect, as well as stings and ovipositors (egg laying organs) in certain species.

Bug eyed
If you look at an insect it can be pretty easy to spot their eyes. Big, round and looking like a golf ball. But did you know that insects actually have two different types of eyes?

The big ones we can see are called compound eyes. Compound eyes are made up of hundreds or even thousands of tiny lenses all arranged together that let the insect see a sort of mosaic of the world around it.

The more of these lenses an insect has in each eye, the better it can see.

Dragonflies, for example, have about 30,000 individual lenses in each eye

which is what makes them such good hunters and even allows them to catch other insects, mid-flight, when hunting for prey!

The second type of eye is much smaller and much harder to spot. These are called ocelli. Insects generally have three of these arranged in a triangle on their forehead. Most larvae only have ocelli, but a few have compound eyes, like the larvae of dragonflies.

Ocelli aren’t as complex or powerful as the compound eyes. They can’t focus like our eyes can; all they can do is detect the intensity of the light around the insect. This helps the insect know if it is light or dark, day or night.

See if you can spot the different types of eyes on these insects below. How good do you think their eye sight is based on what we now know about compound eyes and ocelli?

Antennae
Almost all adult and young insects have a single pair of antennae. They use their antennae for sensing their environment, in a similar way that we use our senses of smell and touch to learn things about the world around us. Insect antennae can communicate very complex information.

There are loads of different types of antennae - here are just a few below:

Insects have got all sorts of strange looking antennae, and some can be very hard to spot in the first place.

Mouth parts
Did you know that insects don’t have internal jaws like humans?! All the cutting and chewing they do happens outside their mouth using special mouth parts, before the food is passed into the mouth of the insect for eating.

Insects have evolved all sorts of weird and wonderful mouths, specially adapted for the food they eat.

Legs

All insects have six legs (three pairs), and just like every other part of the animal, these are adapted to suit the environments of each species, so they all look a bit different.

Insects need their legs for walking and running around just like us, but they also have other uses for them too.
- Jumping and climbing (Grasshoppers)
- Digging and handling other objects (Mole crickets)
- Catching prey (Mantids)

While they might all look different, their structure is still the same, and even resembles the bone structure of a human leg as both have a femur, a tibia and tarsus.

Wings (and elytra)
Most insects have two pairs of wings attached to the thorax. Some insects, like beetles, have specially adapted wings called elytra, which act as a hard, protective cover for the second pair of wings below.

Some insects, such as flies, have a much reduced pair of forewings, called halteres, which they use for steering during flight.

Dragonflies are one of the only species of insects to move their two pairs of wings independently when they fly around, whereas most other insects use both pairs of wings together in unison.

There are a few groups of insects without wings, like fleas and lice.

As these animals spend most of their lives crawling around in thick animal fur or feathers and so, over a very long time, have lost their wings entirely!

Some species can look so similar that the only way to tell them apart is to look at the vein patterns in their wings.

 

Glossary

Ecological niches – refers to the role an animal plays in the ecosystem it is part of, such as producer, or predator. It can be filled by different species in different geographical locations and habitats.

Ocelli – a simple eye without sophisticated retina or a compound structure.