Dimorphic Foraging Strategies of a Salticid Spider (Phidippus Audax)

Adult$\male$and$\female$Phidippus audax (Salticidae) have different feeding strategies reflecting major differences in their time budgets and food requirements. Males are 89% as large as$\female \female$(measured by cephalothorax width), but size dimorphism is insufficient to account for differences between their rate and pattern of feeding on flies provided experimentally. The$\male \male$feed at a uniformly low rate throughout adult life. They become sated rapidly and extract less from individual prey as they approach satiation. Individual prey sufficiently large to sate a$\male$spider are discarded before being fully utilized. Both$\male \male$and$\female \female$remove ≈76% of the prey biomass from fully utilized dipteran prey. Adult$\female \female$feed at a high rate until they have developed a large egg mass. They then nearly cease feeding and deposit their eggs. During their period of high feeding,$\female \female$are insatiable and utilize all dipteran prey fully, regardless of prey size or the number of prey previously eaten. Difficult prey, those that require longer handling time than do similarly-size dipteran prey such as highly sclerotized beetles (Dermestes sp.), are consumed less fully by$\male \male$than$\female \female$. Females utilize difficult and easy prey (Diptera) to a similar degree. Because$\male \male$spend the same amount of time handling and feeding on items of similar size regardless of their handling difficulty, they extract less food from difficult prey than from other prey. Both$\male \male$and$\female \female$reject the large milkweed bug (Oncopeltus fasciatus) and are unable to penetrate the cuticle of the lightning beetle (Photuris pennsylvanicus). Males prefer small prey (6 and 19 mg) when offered a choice of 4 (6, 19, 38, and 94 mg) sizes of dipterans. Females prefer intermediate (38 mg) sized prey. Size preferences are more distinct in$\male \male$than$\female \female$, and$\female \female$capture a more even distribution of different prey sizes than$\male \male$. For both sexes the largest portion of prey biomass per spider is contributed by the largest prey selected preferentially. This is true for$\male \male$even though they show a stronger preference for smaller prey.