Arthropods are the most diverse group in the animal kingdom. Among them, the evolutionary record holders are insects, thanks to their ability to adapt to many different ecosystems, both in water and on land. The versatility of arthropods is largely due to chitin, a substance that forms their hard outer covering as well as their wings and other flexible parts. Like cellulose, the building block of plant cell walls, chitin is made up of glucose molecules, but it also contains nitrogen, producing a firm structure.
Chitin is the main component of the arthropod exoskeleton, the first rigid form to have evolved in multicellular organisms: arthropods produced chitin 550 million years ago. Secreted by the epidermis, or soft, skin-like outer layer, chitin combines with other compounds to form the waxy, water-repellent cuticle.
A remarkably hard yet flexible material, chitin strengthens insect mandibles to cut through rock and metal, and provides elasticity between rigid body segments, allowing speed and agility. The tiny, delicate scales covering insects such as butterflies also contain chitin. It is an integral part of the thin tracheal tubes that make up their respiratory system and the hairs that collect pollen.
It seems that chitin can do almost anything except allow an exoskeleton to grow. Thus, to grow, arthropods must molt. Occasionally, they have no choice but to temporarily shed their chitinous protective covering in exchange for some room to grow.
This story originally appeared in the June 2021 issue of National Geographic’s Hungarian edition.