Eri silkworm spins mechanically robust silk fibers regardless of reeling speed

Wild silkworms survive in environmental habitats in which temperature and humidity vary based on the weather. In contrast, domesticated silkworms live in mild environments where temperature and humidity are generally maintained at constant levels. Previous studies showed that the mechanical strengths and molecular orientation of the silk fibers reeled from domesticated silkworms are significantly influenced by the reeling speed. Here, we investigated the effects of reeling speed on the mechanical properties of eri silk fibers produced by wild silkworms, Samia cynthia ricini, which belong to the family of Saturniidae. We found that the structural, morphological and mechanical features of eri silk fibers are maintained irrespective of the reeling speed, in contrast to those of domesticated silkworm silk fibers. The obtained results are useful not only for understanding the biological basis underlying the natural formation of silk fibers but also for contributing to the design of artificial spinning systems for producing synthetic silk fibers.