The Strategic Use of Venom by Spiders

Abstract

Understanding the behaviors by which animals deploy their venoms has been largely neglected compared to other aspects of the evolution and biology of venomous organisms and their venoms. Yet, behavior has long been recognized as a pacemaker for the evolution of morphological, ecological, life history, and other traits, in large part because behavioral responses can expose organisms to or protect them from novel selection pressures. The importance of behavior is especially evident in that venom most often functions through a behavioral act that generates a wound in a target animal through which the toxic secretion must be introduced. As a limited and costly commodity, venom should be deployed strategically and judiciously by those animals that possess it. The chapter summarizes the major aspects of adaptive venom use in animals, and highlights the best documented examples of strategic venom deployment among spiders. These animals, like other venomous taxa, exhibit four major behavioral strategies. First, they are often highly selective when using their venom, discharging it only under certain conditions. Second, they can modulate the quantity of venom they expend in both predatory and defensive contexts, delivering multiple bites or variable quantities within individual doses. Third, at least one study suggests that spiders possess venom gland heterogeneity and therefore deliver varying venom composition with successive venom expulsions. Finally, some evidence suggests that spiders can strategically target the delivery of their weapon at a particularly vulnerable region of their target. Collectively, the evidence suggests a common theme among spiders and other venomous animals for economization and optimization of venom deployment.