  An asymmetric \b{eta}-sheet structure of spider silk is said to induce
optical second harmonic generation. In this paper, using an in-house
non-scanning type femtosecond pulse laser second harmonic generation
microscope, we characterized the behavior of the \b{eta}-sheet of spider silk
under an applied external force. The orientation of the \b{eta}-sheets was more
unidirectional when the silk was extended. One of the origins of the high
mechanical strength of the dragline is suggested to be the physical arrangement
of its \b{eta}-sheets.
