What is the process called when insects shed their exoskeleton to grow?

The process of shedding an exoskeleton to allow for growth in insects is known as molting. During molting, the insect breaks free from its old exoskeleton, allowing it to expand before hardening the new exoskeleton, which supports further growth. This is a critical part of an insect's life cycle, as their exoskeletons do not stretch.

Metamorphosis refers to a more profound transformation that insects undergo during their life cycle, transitioning through various stages from egg to larva, pupa, and finally to adult. Instar describes the specific stages of growth between molts, signifying the different phases an insect goes through, but it does not represent the act itself of shedding the exoskeleton. Evolution is a broader biological concept that refers to the change in the genetic composition of populations over time and is not specific to the growth process of insects. Thus, the term that directly describes the shedding of the old exoskeleton is molting, making it the correct answer.