The Molting Process for Insect Growth

Pros and cons of molting as a growth process

A recently molted woodlouse.
A recently molted woodlouse. Getty Images/Will Heap

Molting, known technically as ecdysis, is literally a period of growth for insects. In humans, an analogy can be drawn to molting as a period of personal transformation, such as the shedding of one's old self and the emergence of a new and improved person.

Insects grow in increments. Each stage of growth ends with molting, the process of shedding and replacing the rigid exoskeleton. People often think molting is the simple act of an insect breaking out of its skin and leaving it behind.

In truth, the process is complex and involves several parts.

When Insects Molt

After an egg hatches, the immature insect feeds and grows. Its exoskeleton is like a shell. Eventually, the larva or nymph must shed its unyielding overcoat to continue its development.

The exoskeleton which serves as its external backbone is used for protection and support. Without an exoskeleton, the insect could not survive. An old exoskeleton is shed when a new one is ready underneath, a process that can take days or weeks.

Understanding the Exoskeleton

To understand how molting occurs, it helps to know the three layers of the insect exoskeleton. The outermost layer is called the cuticle. The cuticle protects the insect against physical injury and water loss, as well as provides rigidity for muscle. It is this outermost layer that sheds during a molt.

Underneath the cuticle is the epidermis. It is responsible for secreting a new cuticle when it is time to shed the old one.

Underneath the epidermis is the basement membrane. This membrane is what separates the insect’s main body from its exoskeleton.

The Process of Molting

In molting, the epidermis separates from the outermost cuticle. Then, the epidermis forms a protective layer around itself and secretes chemicals that break down the insides of the old cuticle.

That protective layer becomes part of the new cuticle. When the epidermis has formed the new cuticle, muscular contractions and air intake cause the insect’s body to swell, thus splitting open the remains of the old cuticle. Finally, the new cuticle hardens. The bug squeezes out from the outgrown exoskeleton.

The insect must continue to swell and expand the new cuticle, so it is large enough to allow room for more growth. The new overcoat is soft and much paler than the former one, but over a few hours, it becomes darker and begins to harden. Within a few days, the insect appears to be a slightly larger copy of its former self.

Pros and Cons of Molting

For some insects, a big benefit to having a system of molting for growth is that it allows damaged tissue and missing limbs to be regenerated or substantially re-formed. Complete regeneration may require a series of molts, the stump becoming a little larger with each molt until it is a normal or nearly back to normal size.

A major disadvantage to having molting as a system of growth is that the animal in question is entirely incapacitated during the process. An insect is completely vulnerable to a predator attack while undergoing molting.