The life cycle of an insect
You may think that as there are about six billion people on the planet humans are the most numerous living things. You would be very wrong. The animal group with the largest number of individuals is the insect group. There may be a billion insects living in a square kilometre around your home.

If you were a typical Earth animal - an insect - this is how you would grow up. Your life cycle begins when your head bursts through your egg shell. On your head are some simple eyes which can detect light and dark but do not let you see clearly. Your mouth is made by a pair of strong jaws which do not open the human way - up and down - but the insect way - side to side. Your first task is to find food and you may use your jaws to bite up your egg shell and swallow it. Next, you would search for more food. With luck, your mother would have laid your egg on a leaf so you do not have far to search. At this time, your body is like a sausage and you wriggle along like a person who has fallen over in a sack race. You also have some legs to help you move the front end of the body and some stumps at the hind end which help you grip onto your food.

Over a few weeks, you feed and grow. The skin of your body also has a section job. It acts as your skeleton. This means it has to be strong and rigid to give you support. It also means that your skin cannot stretch as you grow as human skin does. The way your body solves the problem of growth is to get rid of its skin from time to time. When it does, the new skin underneath is soft. Inside an insect's body are air pipes. You can see the ends of the pipes as tiny circles along the side of an insect's body. They look like the portholes in the side of a ship. When the insect has a new soft skin, it takes in air through its pipes and pumps up its body before the skin becomes hard. Later, after the skin has become hard and supportive again, an insect fills the air space inside its body with flesh.

When you are fully grown, a great change takes place. You moult but do not get a skin to cover your head and body. You get a skin which is like a box and is called a pupa. It traps you inside so that you can no longer move and feed. At this time, parts of your body are broken down and rebuilt into different structures. Instead of the head with simple eyes and tough jaws, you develop large eyes and a mouth in the form of a tube. Instead of a sausage-shaped body with short legs, you grow a body with three pairs of long legs and two pairs of wings. When all the changes are complete you feel the power to break out of your box. After you have climbed out, you hang on the box and pump air into your body. It does not make your body grow but moves up tubes inside your wings and makes them expand.

After you have let your wings extend to their full size, you use muscles to flap them. As your wings go up and down, you can feel them pulling you away from your box. You let go of the box and fly into the air. Your new large eyes let you see more clearly and you fly over the leaves. You are attracted to flowers by their bright colours and sweet smells. As you land on a flower, you uncoil your long tube-like mouth, just as a fire-fighter uncoils a hose. You probe into the flower with the tip of your mouth and find sweet nectar deep inside the petals. You use your mouth like a straw and take a drink. You have now become a butterfly.

Do all insects have caterpillars in their life cycle?
No. When some insects hatch from their eggs, they look like miniature versions of the adults. However, they do not have wings or reproductive organs. This stage in the life cycle is called a nymph. As a nymph grows it moults just like a caterpillar but at no stage does it produce a box round itself called a pupa. It just keeps getting larger. Eventually, at its last moult, it gets its wings and reproductive organs and becomes an adult.

What kinds of insects have nymphs?
Cockroaches, grasshoppers, crickets, locusts and dragonflies are some examples of insects that have nymphs in their life cycles.

How does a ladybird grow up?
A ladybird is really a beetle with brightly coloured wing-cases. If a ladybird had black wing-cases like most other beetles, perhaps people would not be so keen to let one walk on their fingers. All beetles have a life cycle similar to that of the butterfly. When the egg hatches a larva climbs out. We call the larva of a butterfly a caterpillar. The larva of a beetle is often called a grub. When the larva is fully-grown, it changes into a pupa. This is a tough box, which forms around the insect. People sometimes call the pupa of the butterfly a chrysalis. The pupa of other insects does not really have other names. Inside the pupa, the insect changes into the adult and when all the changes are complete it breaks out and begins its adult life.

Do all insects complete their life cycles on land?
No. Some insects have a life cycle where the young stage lives in water and the adult stage lives on land. The mosquito is an example. Its larva lives in stagnant water such as the water in ponds. The larva has gills to breathe oxygen that is in the water. The mosquito larva forms a pupa, which rests at the water surface and has a breathing tube. This breaks through the water surface and allows the changing insect to breathe air. When the adult mosquito emerges, it escapes from the pond surface and flies into the air. It begins a life of feeding on blood or plant juices and searching for a mate. The young stage of the dragonfly also lives in water. It is a nymph.