Sclerotin

Sclerotin is a component of the cuticles of various Arthropoda, most familiarly insects. It is formed by cross-linking members of particular classes of protein molecules, a biochemical process called sclerotization. Technically it amounts to a form of tanning. The resulting material increases the rigidity of an insect's chitinous exoskeleton. 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.