Butterfly Chrsalis hanging

Butterfly Life Cycle: Chrysalis

The transformation of a caterpillar to a butterfly takes place in the chrysalis (pupa).

Butterflies go through a life cycle of 4 stages: egg, larva, pupa and adult. Inside the chrysalis, several things are happening and it is not a “resting” stage. The caterpillar’s old body dies inside the chrysalis and a new body with beautiful wings appears after a couple of weeks.

  The Caterpillar

The caterpillar spends most of its time eating. Hormonal changes occur and the caterpillar loses interest in feeding. When it is time to become an adult, it finds a sheltered safe spot in which to pupate where it transforms itself.

Read more: Caterpillar Anatomy

  The Magical Transformation

Metamorphosis is the process in which a caterpillar transforms into a butterfly. All caterpillars create a protective shell known as a chrysalis, but the specifics differ from species to species. Some chrysalis hang upside down but others support themselves on tree branches or create a silk hammock.

  Monarch Butterfly, Danaus plexipus

After wandering for a while, the caterpillar makes a simple silk pad on the underside of a branch or twig. It uses a hook-covered appendage called a cremaster to attach itself to this pad. It twists around, embedding its cremaster firmly in the silk. Then, it sheds its skin, revealing the chrysalis. The chrysalis starts out soft and skin-like, but gradually hardens to form a protective shell. The chrysalis hangs upside down from the cremaster until the butterfly is ready to eclose, emerge as an adult from the pupa.

  Another Strategy

Other caterpillars use variations on this process when they pupate. Instead of hanging upside down, some make a silk sling from a tree branch to support them as they pupate right-side up. Others create a silk hammock to support their chrysalis.

It's easy to think of a chrysalis as something a caterpillar makes, like a cocoon, but this isn't really true.

  The Biology of the Transformation

The transformation itself is amazing. The change inside the chrysalis is slow and gradual. The caterpillar’s body digests itself from the inside out. The caterpillar is attacked by the same sort of juices that it used in its earlier life to digest food. Many of the organs are hidden in the caterpillar and they take a new form within the chrysalis.

The body breaks itself down into imaginal cells, which are undifferentiated — like stem cells, they can become any type of cell. The imaginal cells put themselves back together into a new shape. But not all the tissues are destroyed. Some old tissues pass onto the insect's new body. One imaginal disk will become a wing and there are imiginal disks that form the legs, antennae and the other organs of the butterfly.

This process of complete transformation is known as holometabolism. The amount of time required to transform completely varies from one species to another, but in general it takes about 2 weeks. For species that survive the winter by staying in the chrysalis, it can take months.

  The New Body Is Formed

Swallowtail butterfly emerging from its chrysalis

During the first three to four days, the chrysalis is a little bag filled with rich fluid. The cells use the fluid to grow and form a new body. Some parts of the caterpillars’ body are more or less unchanged, including the legs.

Underneath a caterpillar’s skin the beginnings of wings form before it sheds its skin for the last time. Inside the chrysalis, the butterflies’ wings are fully formed. A butterfly's sucking mouth parts are formed from the caterpillar's chewing mouth parts.

  Changing Color

The chrysalis loses nearly half of its weight because the metamorphosis consumes energy. During the transformation, the chrysalis cannot excrete or defecate. The waste products accumulate and there is nitrogenous waste that can be seen as a reddish-colored liquid under the butterfly after it emerges. Complete transformation takes about 2 weeks.

If a caterpillar enters the pupae stage during the cooler autumn months, then it may wait out winter by going into diapause. Diapause is a stage like hibernation, where all growth stops. It will continue its transformation and emerge once the weather warms up in spring. In this case the transformations can take a several months.

A couple of days before the butterfly emerges, the chrysalis changes color, The butterfly's patterns and color can be seen though the chrysalis. The butterfly breaks out of the protective chrysalis and pumps blood into its newly formed wings. Then it flies away.

Further Information:

 Butterflies and Moths of North America
 Southern Wisconsin Butterfly Assn (NABA)
 The Butterfly Site

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