Radius construction and structure in the orb-web of Zilla diodia (Araneidae)

In orb-webs, the tension of the sticky spiral produces a centripetal force on the radii, resulting in an increase in tension along each radius from th e centre of the web to the periphery. Zilla diodia (Walckenaer, 1802) atypi cal of araneids, was found to adapt the structure of its radii to this tens ion gradient by building radii that are double stranded at the periphery of the web and single stranded near the centre. Furthermore, the proportion o f each radius that is doubled was found to be larger in the upper part of t he web - where the overall tensions in the radii are known to be higher - t han in the lower part of the web, suggesting that the spider adjusts the pr oportion of each radius that is doubled to the overall tension in the radiu s.