Draglines out of Nephila clavata spiders were automatically wound around a rectangular frame of 5 cm × 10 cm, using an apparatus developed by the author. The reflectance in the visible rays below 450 nm for draglines out of mature spiders decreased with the irradiation of ultraviolet rays and especially the reflectance in the ultraviolet rays decreased markedly. However, the reflectance for draglines out of juvenile spiders did not change so much by irradiation of ultraviolet rays. The irradiation of ultraviolet rays decreased the mechanical breaking strength of draglines markedly.
　The reflectance in the region of visible and ultraviolet rays was also studied for silks prepared from silkworm. The irradiation of ultraviolet rays decreased the reflectance near 300 nm 〜 450 nm markedly. It was shown that the intensity of radicals induced by the irradiation of ultraviolet rays was much higher for silks than for spider's draglines.
　These findings suggest that the spider's draglines are more resistant to the irradiation of ultraviolet rays than the silks from silkworm and that the draglines will be useful as new materials for textile.

DESCENTE SPORTS SCIENCE Vol.20/THE DESCENTE AND ISHIMOTO MEMORIAL FOUNDATION FOR THE PROMOTION SPORTS SCIENCE