The FWHM of the (200) peak was greater in A. keyserlingi silks when protein deprived compared to when protein fed. Crystallinity, on the other hand, was greater in the silks of protein fed A. keyserlingi (Supporting Information, S4A Table). These findings and the greater long period in the silk of protein deprived A. keyserlingi indicate that the crystalline nanostructures in their silks were stacked more densely when the spiders were protein fed, and were more aligned and stretched when they were protein deprived. We considered it likely that the greater alignment of the crystalline region proteins in the silks of protein deprived A. keyserlingi explains the high extensibility of their silks. FWHM at the amorphous halo was greater in the silks of protein deprived compared to protein fed N. plumipes (S4D Table). This result, and the greater ultimate strength in the silk of protein fed N. plumipes, indicated that variability in the non-crystalline nanostructures primarily influenced their silk mechanical properties. SAXS/WAXS did not detect any significant nanostructural shifts across treatment for E. transmarina, L. hasselti and P. graeffei silks (Supporting Information, S4B, S4C and S4E Table).