Wrap attack activates web-decorating behavior in Argiope spiders

Various orb-weaving spiders add extra silk structures—‘‘web decorations’’—to their webs. The adaptive value of these web deco-rations is still unclear, and the suite of functional hypotheses remains controversial. Spiders in the genus Argiope decorate their webs with densely woven zigzag ribbons made of fibrous aciniform silk. This type of silk is also used by the spiders for ‘‘wrap attacks’’ to immobilize the prey by wrapping it with a dense silk cover. Previous studies suggested that the spiders use accumulated excess silk for building web decorations due to a constant secretion in the aciniform glands. We test if this hypothesis holds for 3 species, which construct different types of web decorations: linear in Argiope bruennichi, irregular in Argiope sector, and cruciate in Argiope keyserlingi. We show that depletion of aciniform silk has a stimulating effect on web-decorating behavior in 3 species of Argiope. The aciniform glands apparently readily overcompensated experimentally induced silk losses, and so silk depletion may result in the activation of the according glands. We suggest that the aciniform gland activation might be an important mechanism for Argiope’s wrap attack to ensure sufficient wrapping of silk under high prey density and repeated wrapping events. The web decorations might function as a mechanism to maintain high gland activity, thereby maximizing the efficiency of the wrap attack strategy of Argiope. Key words: aciniform silk, Argiope, capture strategy, gland activation, web decorations. [Behav Ecol 19:799–804 (2008)] Predators either actively search and hunt for prey or in-conspicuously wait for potential prey. If combined with high-speed locomotion, active hunting is often highly energy consuming. Sit and wait predators save this energy but have t