Nanoscale fibers of natural silks of Bombyx mori and Nephila clavipes were produced from solutions in hexafluoro-2-propanol. The electrospun fibers were observed by optical, scanning electron, and transmission electron microscopy. These nanofibers showed optical retardation. appeared to have a circular cross-section, and were thermally stable under nitrogen to 280 degreesC (N. clavipes) and to 245 degreesC (B. mori). The diameter of the fibers ranged from approximately 6.5-200 nm making them orders of magnitudes smaller than the natural silks spun by most silkworms and spiders. The smallest fiber diameters correspond to 200 molecules in the cross section of the N. clavipes fibers and 150 in B. mori. Electron diffraction patterns of annealed electrospun fibers of B. mori and N. clavipes exhibit diffraction peaks demonstrating, orientational and crystalline order comparable to that of naturally spun silks. (C) 2004 Elsevier Ltd. All rights reserved.