Quarterly Journal of Microscopical Science, Vol s3-103, 557-571, Copyright © 1962 by Company of Biologists

The Control of Dragline Spinning in the Garden Spider

¹ Department of Zoology, University of Bristol

A study of the tarsal claws, the spinning apparatus, and other factors affecting dragline spinning has been made using certain orb-web spiders, principally Araneus diadematus. The structure of the tarsal claws suggests that they are incapable of smoothly controlling the speed at which the silk thread is extracted, although they can grip and release the thread quickly.

Evidence is presented that smooth control of spinning is achieved through the interaction of the intra-abdominal pressure and the control valve which lies in the silk duct. The intra-abdominal pressure is shown to be equivalent to from 3 to 4 cm of mercury, and to be responsible for moving the fluid silk out of the gland and up the duct. The experimental results also suggest that the control valve regulates the amount of fluid silk available for spinning as a thread and that it also acts as the functional spinning orifice, its aperture controlling the diameter of the thread spun.