Fibroin is an insoluble protein present in silk created by spiders, the larvae of Bombyx mori, other moth genera such as Antheraea, Cricula, Samia and Gonometa, and numerous other insects. Silk in its raw state consists of two main proteins, sericin and fibroin, with a glue-like layer of sericin coating two singular filaments of fibroin called brins.