Melanin polymers are synthesized in the cuticle from dopamine, and to a lesser extent from L-DOPA, that are secreted by epidermal cells into the cuticular matrix. Following a series of oxidation and isomerization/tautomerization reactions, dopamine is converted to 5,6-dihydroxyindole (DHI) while L-DOPA is converted to DHI or 5,6-dihydroxyindole-2-carboxylic acid (DHICA). The addition of L-cysteine during the first steps results in the formation of benzothiazole derivatives. Oxidative polymerization of DHICA produces light brown eumelanin, while oxidative polymerization of DHI produces brown to black eumelanin. Yellow to red pheomelanin is produced from benzothiazole derivatives. In addition to its role in cuticle pigmentation and thermoregulation, melanin is also produced in the hemolymph as part of the immune defense mechanism against pathogens and wound healing. (Adapted from PMID:27775611 and FBrf0258382.)