While there is broad micro-scale homogeneity in the MA silks of Araneoid spiders, our measurements found that variations in the gene expression, amino acid compositions, and nanostructures, further induce mechanical property variations between and within species. Our modelling found nanostructural variations to primarily influence silk extensibility and toughness while variations in the alignment of the crystalline and non-crystalline proteins influenced ultimate strength independent of MaSp expressions. Our study provides insights into the nanoscale mechanisms of nutritionally induced spider silk property variability by showing how spidroin expression and nanostructures affect spider silk mechanical property variations in different species. These insights further our understanding of MA silk property variability at multiple levels which is imperative if materials that match the performance of naturally spun spider silks are to one day be synthesized.