What phenomenon makes molting necessary for insects?

The necessity of molting in insects primarily relates to their size increase. Insects, unlike vertebrates, have an exoskeleton made of chitin that does not stretch. As an insect grows, it reaches a point where its exoskeleton becomes too tight and restrictive, preventing further growth. To overcome this limitation, the insect must undergo molting, a process also known as ecdysis. During molting, the old exoskeleton is shed, allowing the insect to emerge with a new, larger exoskeleton underneath. This new exoskeleton is initially soft and flexible, allowing the insect to grow until it hardens and becomes more rigid, thus accommodating the increase in size as the insect matures through its life stages.

This process is crucial for the insect's development and growth, enabling it to transition from larval stages to adulthood. While other elements, such as body parts or dietary needs, may affect an insect's life cycle or adaptability, they do not serve as the primary drivers for the necessity of molting in the same manner that size increase does.