The silk nanostructures varied in response to protein feeding/deprivation among the five spiders (see Supporting Information, S4 Table). The SAXS images and subsequent intensity vs scattering vector (q) plots for each spider are shown in Fig 2 and Fig 3 respectively. Examples of two dimensional WAXS images are shown in Fig 4 and the subsequent intensity vs 2θ plots in Fig 5. The azimuthal angles at the (200) and (120) diffraction peaks are in the Supporting Information (see S1 Fig and S2 Fig, respectively). From the various plots we calculated a greater long period in A. keyserlingi silks when the spiders were protein deprived compared to when they were protein fed. Within species, the nanostructures generally shifted in the same direction as the mechanical properties we predicted them to affect, e.g. long period and/or FWHM of the amorphous halo varied with extensibility in A. keyerlingi and N. plumipes (Supporting Information, S4 Table). We thus expect the structural variations to explain much of the variation in mechanical properties.