The structure of a single thread of Nephila edulis silk has been studied by in situ X-ray diffraction from a living spider. A systematic increase of orientational order with increasing silking speed up to 40 mm s(-1) was observed. Within a few mm from the spinnerets exit, crystalline domains with a beta -poly(L-alanine) structure were observed. The data also suggest an increase in crystalline fraction in the immediate vicinity of the spigot exit.