| I investigated the behavioral ecology of venom and venom use by the western widow spider (Latrodectus hesperus), emphasizing the role of ontogeny. In an introductory paper, I reviewed existing definitions of venom and poison, and refined these by adding a third category of toxic biological secretions: toxungen. These three can be distinguished by mode of toxin delivery and presence of a wound. In the first of four empirical studies, I investigated venom use by adult females in the context of threat assessment. A single brief poke at the lowest threat level elicited primarily avoidance responses ("move" and "retract"), repeated prodding at medium threat incited increased silk-flicking, and gentle pinching at highest threat provoked increased biting. Spiders modulated venom expenditure by delivering 2.2-fold more venom per bite when pinched on the body compared to a leg, and 2.3-fold more venom when target presentations were separated by a long (5-min) rather than a short (5-sec) interval. The second study investigated the ontogenetic development of defensive behaviors. Spiders relied largely on non-combative behaviors early in life and switched to more combative behaviors, including silk flicking and biting, as they increased in size. Sex differences in behavior were comparatively negligible. Spiders habituated to the repeated testing by exhibiting fewer combative behaviors than naïve spiders upon reaching adult size. In the third study, I developed an ethogram of the prey capture sequence of adult females feeding on crickets (Acheta domesticus) approximately 1.5 times their size. I identified 21 behaviors exhibited during three major phases: detection, immobilization, and prey manipulation. Spiders delivered an average of 15.2 (range 0–31) brief bites, with initial bites primarily to a leg. In the fourth study, I investigated ontogenetic and sexual variation in venom composition. Initial results requiring validation by improved methodology suggested that female venom becomes increasingly complex with age, whereas male demonstrates a more complex pattern. This dissertation represents the first major study of defensive venom metering in spiders. My findings support a growing body of literature suggesting that spiders are capable of cognition, and evaluate information from their body and environment when making decisions. |
