Despite extensive study of poisonous and venomous organisms and the toxins they produce, a review of the literature reveals inconsistency and ambiguity in the definitions of 'poison' and 'venom'. These two terms are frequently conflated with one another, and with the more general term, 'toxin.' We therefore clarify distinctions among three major classes of toxins (biological, environmental, and anthropogenic or man-made), evaluate prior definitions of venom which differentiate it from poison, and propose more rigorous definitions for poison and venom based on differences in mechanism of delivery. We also introduce a new term, 'toxungen', thereby partitioning toxic biological secretions into three categories: poisons lacking a delivery mechanism, i.e. ingested, inhaled, or absorbed across the body surface; toxungens delivered to the body surface without an accompanying wound; and venoms, delivered to internal tissues via creation of a wound. We further propose a system to classify toxic organisms with respect to delivery mechanism (absent versus present), source (autogenous versus heterogenous), and storage of toxins (aglandular versus glandular). As examples, a frog that acquires toxins from its diet, stores the secretion within cutaneous glands, and transfers the secretion upon contact or ingestion would be heteroglandular-poisonous; an ant that produces its own toxins, stores the secretion in a gland, and sprays it for defence would be autoglandular-toxungenous; and an anemone that produces its own toxins within specialized cells that deliver the secretion via a penetrating wound would be autoaglandular-venomous. Adoption of our scheme should benefit our understanding of both proximate and ultimate causes in the evolution of these toxins.

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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.

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