Molting occurs when and because they need to grow. Crayfish have exoskeletons which means they have a hard, protective shell on the outer layer of their body. They need to grow out of their shells to...
crayfish : early 14c., crevis, from O.Fr. crevice "crayfish" (13c., Mod.Fr. écrevisse), probably from Frankish *krebitja or a similar Germanic word that is a dim. form of the root of crab (1); e.g....