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Butterfly Life Cycle — Metamorphosis

Butterfly Life Cycle

What causes the radical transformation from caterpillar to butterfly?

How does a caterpillar rearrange itself into a butterfly?

What happens inside a chrysalis or cocoon?

  The Biological Process

Metamorphosis is a biological process by which an animal physically develops after birth or hatching, involving a conspicuous and relatively abrupt change in the animal's body structure through cell growth and differentiation.

In insects growth and metamorphosis are controlled by hormones synthesized by endocrine glands near the front of the body. Neurosecretory cells in an insect's brain secrete a hormone that activates glands, which secrete a second hormone to produce juvenile hormone, which prevents the development of adult characteristics during the shedding of the outer cuticle (skin).

Metamorphosis is a Greek work meaning transformation or change in shape. Butterflies undergo a complete metamorphosis which means that the butterfly looks different in each stage: egg, larva, pupae and adult.

  Egg

Monarch Butterfly (Danaus plexippus) Eggs The butterfly egg is spherical or ovate shaped, varying in color and size. It is covered by chorion, a hard shell that protects the egg, and is lined with a waxy layer that prevents dehydration. It is full of nutrients and is commonly the first meal for the newly hatched larva. There is a small opening called a micropyle which allows sperm to enter the egg for fertilization while inside the female.

To protect the egg and embryo that is forming, the eggs are attached to a leaf by the butterfly using an adhesive-like substance that glues the egg to the plant leaf. The nature of the “glue” is still fairly unknown in the scientific community. For protection, the eggs are often laid on the underneath side of the leaf so as not to be visible to predators. It is essential for the eggs to be laid on the host plant for that particular butterfly species. Eggs are sometimes laid in groups, although many butterflies such as the Monarch lay their eggs singly. The average time for the embryo to develop is 7-14 days but in instances where the egg is the overwintering stage, the embryo may take months to develop.

Read More: Butterfly Life Cycle: Egg

  Caterpillar (Larvae)

To protect the egg and embryo that is forming, the eggs are attached to a leaf by the butterfly using an adhesive-like substance that glues the egg to the plant leaf. The nature of the “glue” is still fairly unknown in the scientific community. For protection, the eggs are often laid on the underneath side of the leaf so as not to be visible to predators. It is essential for the eggs to be laid on the host plant for that particular butterfly species. Eggs are sometimes laid in groups, although many butterflies such as the Monarch lay their eggs singly. The average time for the embryo to develop is 7-14 days but in instances where the egg is the overwintering stage, the embryo may take months to develop.

American Lady (Vanessa virginiensis ) Caterpillar A caterpillar grows really fast. This is because they eat a lot. A caterpillar is really small when it is born. It starts to grow fast. This is because it eats all the time. When a butterfly 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

Caterpillars 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 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. Most butterflies have 5-6 instars.

Read More: Butterfly Life Cycle: Caterpillar

  Chrysalis (Pupae)

Chrysalis of Gulf Fruitillary (Agraulis vanillae) Butterfly The pupa, though sedentary, is a stage of great internal turmoil and transformation. Nearly all of the larval tissues and organs (eyes, mouth parts, legs, glands, muscles) will be digested and reorganized into the body of the adult butterfly. Prior to pupation, the larva loses much of its patterning and its length decreases. In addition, the gut is evacuated.

The pupa stage of the butterfly’s life cycle is a time for complete change. The pupa is also known as a chrysalis and is a vessel in which the slow moving caterpillar changes into a winged butterfly. The process begins with the prothoracicotropic hormone (PTTH) triggering the caterpillar to quit eating and start wandering to a place to pupate, which is usually on twigs or other safe areas around their host plants but not necessarily on the host plants. Some butterfly species that over winter as a chrysalis may pupate in the leaf litter close to the ground.

The chrysalis is immobile so it is important that it be camouflaged into the environment. For example, the Spicebush Swallowtail’s chrysalis takes on a brown or green color depending on the color of the environment. Many chrysalides are leaf shaped and vary in color from yellow, brown, green to silver and gold. Some chrysalides have the ability to wiggle and make a hissing sound in order to frighten predators.

This 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 mouth parts of the caterpillar are transformed into the sucking mouth parts of the butterfly.

Read More: Butterfly Life Cycle: Chrysalis

  Adult

Henry's Elfin (Callaphrys henrici) Butterfly Adults emerge from the pupa with short wings that must be expanded with hemolymph. Newly emerged adults, especially those with large, heavy wings, must be able to hang from a twig or other object to successfully enlarge their wings.

The transformation from a hardly recognizable creature to a flight-ready adult is rapid, occurring over a span of only 20-60 minutes. It is one of nature's most captivating and awe-inspiring phenomena. Some species cycle through an entire generation in as few as 4-5 weeks with the Monarch butterfly being a familiar example.

Near the end of each stage, the larva undergoes a process called apolysis, mediated by the release of a series of hormones. During this phase, the cuticle, a tough outer layer made of a mixture of chitin and specialized proteins, is released from the softer epidermis beneath, and the epidermis begins to form a new cuticle. At the end of each instar, the larva molts, the old cuticle splits and the new cuticle expands, rapidly hardening and developing pigment.

Development of butterfly wing patterns begins by the last larval instar. Internally, most of the body cavity is taken up by the gut, but there may also be large silk glands, and special glands which secrete distasteful or toxic substances. The developing wings are present in later stage instars and the gonads start development in the egg stage

Butterflies spin the button of silk to which the chrysalis will attach. Most butterflies have 5-6 instars.

Vocabulary
Apolysis The process where the cuticle separates from the epidermis when a larva is moulting.
Chitin A fibrous substance forming the major constituent in the exoskeleton of butterflies.
Endocrine Glands A gland that secretes a hormone into the bloodstream.
Hemolymph The transformation stage between the larva and the adult.
Instar A phase between 2 periods of molting in the development of the butterfly larval.
Prothoracicotropic Hormone A hormone acts on the prothoracic glands, which respond by releasing a molting hormone .
Pupation To go through metamorphosis and become a pupa.

Further Information:

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

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