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We studied physiological conditions during the spinning of dragline silk by the garden cross spider, Araneus diadematus. Silk is converted from the liquid feedstock in the gland into a solid thread via a tapering tubular duct and exits at a spigot. The distal part of the tubule appears specialized for ion transport and the management of the pH inside the lumen. Thus, it appears that spider silk in vivo, like some industrial polymers in vitro, is spun through an acid bath.
Vollrath et al. (Thu,) studied this question.