Amino acid compositions of the MA silks varied across treatments and the type of variations found differed for each of the spiders. For instance, we found a reduction in the proline, alanine and glycine compositions of A. keyserlingi silk when protein deprived (Supporting Information, S5 Table). A reduction in proline composition was, however, detected in N. plumipes and P. graeffeii MA silks when they were protein fed.