Britannica Sources used in this answer

How does an insect cuticle form an exoskeleton?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

A pangolin walks through grass with a blue circle around it and the word endangered written in white across the image. — Integument The pangolin is the only mammal in the world covered in scales.

An insect's exoskeleton is formed by the epidermis, which secretes a tough, multilayered cuticle. This cuticle is primarily composed of chitin—a high-molecular-weight polysaccharide—embedded in a protein matrix.12

The transformation into a rigid exoskeleton involves several key processes:

Sclerotization: The new cuticle undergoes a chemical hardening process called sclerotization. During this stage, quinones create cross-links between cuticular proteins and chitin, forming a natural plastic known as sclerotin.13
Expansion: After ecdysis (the shedding of the old cuticle), the insect expands its soft, new cuticle by increasing hemolymph pressure through the intake of air or water.3
Waterproofing: To prevent desiccation, the surface is covered by a layer of wax, which is often protected by a thin, cementlike substance secreted by dermal glands.1

Because the cuticle is a rigid structure, insects must periodically undergo molting to grow, replacing the old exoskeleton with a new, larger one.13