The life cycle of an animal is the journey from the start of its life all the way to the end of its life. The four stages of the life cycle are birth, growth, reproduction, and death.

Animals have different life cycles depending on the type of animal it is, for example, the life cycle of insects is very different from the life cycle of mammals. Insects are born from eggs, whereas mammals develop as embryos inside the mother’s bodies.

Life cycles also differ for animals as some animal life cycles can last days, weeks, or longer. Some animals go through transformations during their growing stages such as amphibians and insects. This process is called metamorphosis. 

Let’s learn about the life cycles of:

• Insects
• Amphibians
• Birds
• Mammals

What is the life cycle of an insect?

First, the insect lays eggs. The eggs vary in shape and size depending on the species. The time it takes for the egg to hatch also varies between species. A larva is an immature form of an insect, it hatches from the eggs. The larva then becomes a pupa and it changes into an adult insect.

An example of this is a butterfly.

First, the butterfly lays eggs on the leaves of a plant or the stem of a plant. Inside the eggs, caterpillars begin to grow. When a caterpillar is large enough it leaves the egg by eating it. The caterpillar feeds off the leaves of the host plant and shed skin during this time too. After the caterpillar has fully grown, it forms itself into a pupa (chrysalis). This is a type of vessel in which the caterpillar changes into a butterfly. This stage can last a few weeks or months. Once the butterfly is ready, the pupa splits open and the butterfly emerges. It’s newly developed wings are not suitable for flying at first as they are soft, wet, and winkled. However, its wings are dry, and the butterfly leaves and flies away. Throughout the growth process, the butterfly undergoes metamorphosis. 

What is the life cycle of an amphibian?

First eggs are laid in the water, the amphibian begins to develop in the eggs. The amphibian hatches from the eggs and continues to grow and adapt in the water until they are adults. 

An example of this is a frog. 

First, an adult frog lays hundreds of tiny eggs in the water. Each egg has a tiny tadpole embryo surrounded by jelly. A tadpole begins to form in the egg as it develops a head and a tail. After a few weeks, the tadpole hatches out from its egg. It uses its gills to get oxygen from the water and feeds off the jelly mass surrounding it. The tadpole does not have any legs yet so after a few weeks, it grows its back legs and then it grows its front legs. Its tail shrinks away and the baby frog emerges out of the water. The baby frog continues to grow into an adult frog and it uses its lungs to breathe. Throughout the growth process, the frog undergoes metamorphosis. 

What is the life cycle of a bird?

First, a bird lays eggs in a nest. The baby bird develops in the egg and once it has fully developed it will begin to crack the egg in order to get out of it. The chick continues to grow until adulthood. 

An example of this is a chicken. 

First, the female chicken lays an egg. Inside the fertilised egg a chick begins to grow. The chick inside the egg uses the egg yolk for nutrition and growth. During the incubation time, the hen keeps the temperature stable in order for the chick to develop. Once the chick inside the egg has developed, it cracks the egg open and gets out of it as they are also able to walk straight away. Chicks have soft feathers called ‘down’. The chick continues to grow into an adult hen or rooster. 

A female chicken is known as a hen, and a male chicken is known as a rooster. Hens do not need to mate with roosters in order to lay eggs, however in order for an egg to develop into a chick, it needs to be fertilised. The eggs that we buy from the supermarkets are unfertilised. 

What is the life cycle of a mammal?

The mammal life cycle takes place inside the body of a female. The reproductive system consists of the tissues, glands, and organs involved in reproduction. Reproduction is the process in which organisms make more organisms using the male and female reproductive systems.

The reproductive system differs in males and females. It is where the process of fertilisation occurs. The process of human reproduction consists of the fusion of gametes (sex cells) – the male gamete is the sperm, and the female gamete is the egg.

First the sperm fertilises an egg – this fertilised egg is called a zygote. Following this, the zygote develops into an embryo and then develops into a foetus. The female then gives birth to the baby. A human baby then goes through the life stages: childhood, adolescence, adulthood, and then old age.