  We demonstrate that spider draglines exhibit a fatigueless response in
extreme cyclic torsion up to its breaking limit. The well defined Raman bands
at $1095$ and $1245 cm^{-1}$ shifted linearly towards lower wavenumbers versus
increasing twist in both clockwise and counter-clockwise directions. Under
thousands of continuous loading cycles of twist strain approaching its breaking
limit, all the Raman bands were preserved and the characteristic Raman peak
shifts were found to be reversible. Besides, nanoscale surface profile of the
worked silk appeared as good as the pristine silk. This unique fatigueless
twist response of draglines, facilitated by reversible deformation of protein
molecules, could find applications in durable miniatured devices.
