Metamorphosis

Butterflies and moths go through a life cycle known as complete metamorphosis. The stages of their life cycle include: egg, larva, pupa, and adult. Below is a description of each life stage, as well as photographs showing each stage in the life cycle of Papilio polytes, the Common Mormon Butterfly.

This photograph shows a swallowtail egg on the bottom surface of a citrus leaf. Swallowtail females typically lay only one egg on a leaf, but each species of butterfly has its own particular "style" of laying eggs. Some butterflies lay their eggs in clusters, and some butterflies lay their eggs on the upper surface of the leaf.

Every butterfly begins its life as an EGG. Female butterflies are very picky about where they lay their eggs! This is because caterpillars are very picky about what they will eat! Each species of butterfly will only eat a single plant (or group of closely related plants) as caterpillars. This particular plant that a caterpillar must have is called the HOST PLANT for that species of butterfly (or moth).

This photograph is a picture of a first instar caterpillar of the butterfly species Papilio polytes (the Common Mormon).

When a butterfly or moth larva (also known as a caterpillar) first hatches from its egg, it is very small! This young caterpillar is referred to as a FIRST INSTAR caterpillar. A caterpillar has only one job: to eat! Many species of caterpillars begin their feast by eating their egg shell, which contains plenty of nutrients. Other species of caterpillars immediately begin eating the tender, small parts of leaves.

This second instar caterpillar may look funny, but this is because it is beginning to molt! The skin around its head, referred to as a "head capsule" has already separated from the caterpillar.

Caterpillars (and all insects) face a challenge as they grow! Unfortunately, their skin cannot grow with them! In order for a caterpillar to grow larger than the skin it had when it hatched, it must make a new, larger skin! The caterpillar does this by first growing a new skin underneath the outer skin. Then, when it is ready, it "sheds" the old skin, and the newer, larger skin underneath is exposed. This process is properly called MOLTING. After the caterpillar has molted for the first time, it is referred to as a SECOND INSTAR, and it has some room to grow.

The second instar caterpillar continues to eat and grow, until it is once again too big for the skin it is in. This caterpillar MOLTS again, and the result is a THIRD INSTAR caterpillar.

The third instar caterpillar also eats and grows until it is too big for its skin. It molts again, and the caterpillar with its new skin is referred to as a FOURTH INSTAR caterpillar.

This fourth instar caterpillar is the same species as the previous three, even though it looks very different! In swallowtail caterpillars, the first three instars often resemble a bird dropping, while the last instars look much more like snakes.

Once more, the caterpillar eats, grows, and molts. This final caterpillar stage, after a total of four molts, is referred to as a FIFTH INSTAR.

This photograph shows a fifth instar caterpillar that is ready to pupate. This caterpillar has already spun a silk "girdle" which attaches it to the stem of the plant in a shape somewhat resembling a "c." This "c" shape is characteristic of swallowtail caterpillars. Other species of butterflies have different positions for pupating.

The fifth instar eats, grows, and becomes too big for its skin. This final caterpillar instar will molt one more time, but the result of this molt is quite different. When the caterpillar molts for the fifth and final time, the new skin underneath forms the outer shell of the CHRYSALIS.

The chrysalis (generically referred to as a pupa), is not a "resting" stage as many people think. Quite to the contrary, a lot is happening to the pupa! The body of the caterpillar is transforming into an adult butterfly! Wings are fully formed (the beginnings of the wings were actually forming underneath the caterpillar's skin before its last molt) in the chrysalis. Antennae are formed and the chewing mouthparts of the caterpillar are transformed into the sucking mouthparts of the butterfly.

After approximately 10 to 14 days as a chrysalis, the butterfly is ready to emerge. When the butterfly emerges from its chrysalis, its wings are small and wet, and the butterfly cannot yet fly. The butterfly must pump fluids from its abdomen through the veins in its wings, which causes the wings to expand to their full size. Next, the wings must dry and the butterfly must exercise flight muscles before it can fly.

Papilio polytes…adult. The main job of an adult butterfly's life is to reproduce. After a female butterfly mates, she searches for the proper host plant to lay her eggs, and the cycle begins again.

Butterflies and moths go through the same stages in their metamorphosis with one difference. Many moths form a cocoon instead of a chrysalis. Moths form cocoons by first spinning a silken "house" around them. Once the cocoon is finished, the moth caterpillar molts for the last time, and forms a pupa inside the cocoon.

Butterflies DO NOT form cocoons, no matter what The Very Hungry Caterpillar says! However, not all moths form cocoons, either! Some moth species pupate underground instead. These caterpillars burrow into the soil or leaf litter, molt to form their pupa, and remain underground until the moth emerges. The newly emerged moth will then crawl out from underground, crawl up onto a surface from which they can hang, and will then expand their wings in preparation for flight.