Sclerotin

[1] The resulting material greatly increases the rigidity of an insect's chitinous exoskeleton, which is otherwise fairly soft.

It is particularly prominent in the thicker, armoured parts of insect and arachnid integument, such as in the biting mouthparts and sclerites of scorpions and beetles.

[3] Sclerotin is biochemically variable; different species incorporate different proteins in different proportions, and the same insect will use different compositions in forming the different components of its body.

For example, a caterpillar may have sclerotized jaws, head capsule, and legs, with the rest of the body soft and membranous.

In general, sclerotized cuticle is formed by cross-linking the various protein molecules with phenolic compounds – a tanning process under enzymatic control.