Wasteful Killing in Urban Black Widows: Gluttony in Response to Food Abundance

Abstract

Current work in behavioral ecology contrasts traditional hypotheses of context-specific adaptation with the suggestion that behaviors are often coupled such that animals exhibit context-general behavioral syndromes. Wasteful killing, the partial consumption and/or abandonment of prey, is a perplexing phenomenon because the costs of this behavior seem high (e.g. energetic loss, risk of injury). Wasteful killing may be the product of a context-specific, adaptive foraging strategy restricted spatially and/or temporally to conditions of prey abundance. Alternatively, wasteful killing may represent a context-general syndrome of high aggression that results in the capture of prey that are not consumed. We investigated the conditions in which a web-building spider the North American black widow (Latrodectus hesperus) participates in wasteful killing. We employed a powerful repeated-measures design that reduces error variance by controlling for individual differences. Across the adult life cycle of female spiders collected from urban habitats throughout Phoenix, AZ, we repeatedly measured each spider’s foraging voracity and wastefulness after varied periods of food restriction (2, 7, and 14 d). While food restriction decreased body condition, condition alone was a poor predictor of voracity and wasteful killing. Our results indicate that previous food restriction i) shortens latency to attack, ii) heightens the number of prey killed per trial, and iii) reduces wastefulness. Latency to attack and wasteful killing were neither repeatable within individuals nor correlated with each other and therefore appear unlikely to be components of a behavioral syndrome. We discuss other possible benefits for wasteful killing in the contexts of predation risk and mate attraction.