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.

[2] As it matures, freshly formed sclerotin becomes a hard, horn-like substance with a range of yellow-brown colors.

[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.

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