Do stabilimenta in orb webs attract prey or defend spiders?

Orb-weaving spiders are ideal organisms for the study of conflict between behavioral investments in foraging and defense because their webs provide physical manifestations of those investments. We examined the impact of including stabilimenta, designs of bright-white noncapture silk, at the center of orb webs for foraging and defense in Argiope aurantia. Our findings suggest that stabilimentum building is a defensive behavior, supporting the "web advertisement" hypothesis that the high visibility of stabilimenta can prevent birds from flying through webs. Yet, spiders often do not include stabilimenta in their webs, indicating that a serious cost is associated with them. We also show through comparison of paired webs with and without stabilimenta, that stabilimenta reduce the prey capture success of spiders by almost 30%. This demonstrates the potential impact that defensive behaviors of spiders can have on their foraging success and suggests that much of the variation in stabilimenta may be accounted for by a cost-benefit trade-off made when including stabilimenta in webs.