Fifty-six N. clavipes spiders from the same region of Florida were kept in captivity under the same conditions and fed a similar diet of crickets. Their major ampulate gglands were forcibly silked. Dates, silking times, and the colors of the dragline silk produced were recorded. The colors ranged from all white through various combinations of white and yellow upon different silkings to all yellow. If a spider had been producing white silk for at least 4 h, the color being produced could suddenly change to yellow 38% of the time. These observations indicate that factors beyond diet and environment influence the color of silk produced in captivity by forcible silking. They also indicate that the spiders store both pigmented and unpigmented silks and that some aspect of forcible silking precludes the spiders' choosing the color. The yellow and white silks exhibit similar exterior surface morphologies as well as similar tensile properties. (C) 2004 Elsevier Ltd. All rights reserved.