Methanol, ethanol, and isopropanol do not radially swell or produce supercontrac tion (SC) of spider major ampullate silk fibers. Their aqueous solutions do so at rates associated with water concentrations, but produce no levels of SC ratios other than those expected of water Itself. Saturated aqueous solutions of NaSCN and LiBr produce swelling and lowered birefringences of axially restrained fibers. On unre strained fibers NaSCN produces further SC. After SC, the wetted fibers can be stretched to their original lengths, and on drying they are in a stable state from which further SC and re-stretching cycles can be repeated. On both unrestrained major and minor ampullate fibers, LiBr causes irreversible gellation. X-ray diffraction measure ments show that the crystallite unit cell rotates due to macro distortion during SC, but is otherwise unchanged. The suggestion is that water ruptures hydrogen bonds between amino and carboxy groups, in the anti-parallel rippled sheet model of silk, to produce radial swelling and allow SC. The internal axial retractive force present in the wetted fibers, which is the driving force for SC, provides axial tension in the restrained condition and in turn prevents access to LiBr, which in the unrestrained condition brings about gellation.

The effects of wetting by water were determined on the dimensions, birefringences, and force-elongation behavior of major and minor ampullate silk fibers from Araneus diadematus Clerck, and major only from Araneus sericatus Clerck and Araneus gemma (McCook) (all family Araneidae). The values obtained at room conditions (RC), in the wetted, restrained (WR) and wetted, axially unrestrained (WU) states, the ratios of these, between states, are reported upon. The unexpected supercontraction of major ampullate fibers, WU, is contrasted with the stabile behavior of those from the minor ampullate gland systems. When dried from the WR state, both types appear to recover their RC properties. But when dried slack from the WU state, the major ampullate fibers undergo the “drawing” phenomenon typical of many man-made protofibers. The techniques required in order to secure data on these fragile (diameters, 0.6–6.0 μm) fibers, are described in some detail.

The force-elongation properties of web fibers produced by the major ampullate gland systems of four species of orb-web-spinning spiders have been determined and compared with the corresponding properties of fibers obtained from the same gland systems by forcible silking. Although all such fibers are highly variable in characteristics, on the average the former are possessed of rupture tenacities of the order of 80 g/tex and rupture elongations of 35%, a combination that gives them an extremely great resistance to failure in extension. There is some indication that fibers obtained by forcible silking without carbon dioxide-induced anesthesia are possessed of similar properties. But forcible silking under complete anesthesia results in the formation of fibers of lower tenacity and tends to produce an even greater variability in morphology and physical properties than is found among web mooring-line fibers from the same species. Techniques are described for the preparation of samples of these very small (3 to 5-micron diameters) and therefore very fragile fibers and for making measurements on them.

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1. The axial retractive stresses that cause the supercontraction of wetted major ampullate silk fibres and the stresses developed upon reextension from the supercontracted condition are quantified and illustrated. 2. The viscoelastic behaviour of major ampullate silk fibres, subjected to the amounts of elongation that would be produced by a spider on its dragline, is described and illustrated. 3. When major ampullate silk fibres are either wet elongated from supercontraction or when dry from initial lengths, viscoelastic stress relaxations are found to be functions of the logarithms of time. Regression curves illustrate these relationships and normalized results are subjected to statistical analyses. 4. Viscoelastic memory of major ampullate silk fibres is illustrated. 5. The characteristics of viscoelastic stress relaxation and viscoelastic memory of major ampullate silk fibres appear not to be associable with taxonomy. 6. Examples are suggested in which supercontraction and stress relaxation act in the formation and placement of major apipullate silk fibres as structural elements of the orb web.