Predator-induced plasticity in web-building behaviour

Many orb-web weaving spiders add conspicuous silken structures, called stabilimenta, to the hub of their webs, which are hypothesized to attract more prey. However, they may also attract predators. Orb spiders should therefore alter their web-building behaviour to minimize predation risk. We tested this hypothesis by experimentally examining web-building responses of the St Andrew cross spider, Argiope versicolor, to predation risk from one of its natural predators, the jumping spider Portia labiata. We randomly assigned A. versicolor juveniles to one of three treatments: (1) blank control (clean blotting paper: no odour from the predator or nonpredator); (2) predator odour cues from P. labiata; and (3) nonpredator control (odour cues from Leucauge decorata). Each individual of A. versicolor was monitored until it had built five consecutive webs (two webs before and three webs after the introduction of predator cues). When exposed to predator cues, the juveniles not only decreased the frequency of stabilimentum building but also refrained from increasing stabilimentum area, capture area and capture silk thread with subsequent webs compared with the blank control and the nonpredator control. Web-building traits, however, were not significantly different between the blank control and the nonpredator control. One plausible explanation is that A. versicolor juveniles can detect and discriminate between predators and nonpredators through olfactory cues and alter stabilimentum building and other web traits in response to the risk of predation. This is the first demonstration of an adaptive, plastic web-building behavioural response induced by chemical cues from a predator.