Viscoelastic Behaviour and Wet Supercontraction of Major Ampullate Silk Fibres of Certain Orb-Web-Building Spiders (Araneae)

Abstract

ABSTRACT The axial retractive stresses that cause the supercontraction of wetted major ampullate silk fibres and the stresses developed upon reextension from the supercontracted condition are quantified and illustrated. The viscoelastic behaviour of major ampullate silk fibres, subjected to the amounts of elongation that would be produced by a spider on its dragline, is described and illustrated. When major ampullate silk fibres are either wet elongated from supercontraction or when dry from initial lengths, viscoelastic stress relaxations are found to be functions of the logarithms of time. Regression curves illustrate these relationships and normalized results are subjected to statistical analyses. Viscoelastic memory of major ampullate silk fibres is illustrated. The characteristics of viscoelastic stress relaxation and viscoelastic memory of major ampullate silk fibres appear not to be associable with taxonomy. Examples are suggested in which supercontraction and stress relaxation act in the formation and placement of major apipullate silk fibres as structural elements of the orb web.